AANEM's top five choosing wisely recommendations

1. Do not perform a needle EMG test for isolated neck or back pain after a motor vehicle accident, as the needle EMG is unlikely to be helpful.

2. Do not perform dermatomal somatosensory evoked potentials for pinched nerve in the neck or back as they are unproven diagnostic procedure.

3. Do not perform a full needle EMG/NCS testing for neck and back pain after trauma.

4. Do not perform NCS without also performing needle EMG for testing for radiculopathy in the neck or back.

5. Do not perform an MRI scan of the spine or brain for patients with only peripheral neuropathy (without signs or symptoms suggesting of brain or spine disorder).

NCS Protocol for Lumbosacral plexopathy

1. Bilateral LE studies needed

2. Motor NCS: 

   • Tibial @ medial ankle and pop fossa to AH

   • Peroneal @ ankle, below fibular neck and above fibular neck (lat pop fossa) to EDB

   • Peroneal @ below fibular neck and above fibular neck (lat. pop. fossa) to TA

   • Femoral @ inguinal lig to rectus femoris. 

3. Sensory NCS:

   • Sural

   • Sup peroneal 

   • Saphenous 

4. Tibial and peroneal F studies

5. H reflex

6. If sx are bilateral do UE studies to r/o polyneuropathy

EMG needle protocol for Lumbosacral plexopathy

1. 2 or more femoral inn muscles:  VL, ilacus

2. 1 or more obturator inn. muscles: AL

3. Inf gluteal inn: Gluteus max

4. Sup gluteal inn: Gluteus medius, TFL

5. Sciatic inn: Biceps femoris

6. 2 or more tibial inn: MG, TP, FDL

7. 2 or more peroneal inn: TA, EHL, PL

8. Paraspinalis: L2, L3, L4, L5, S1

Upper lumbar plexopathy: 

• Sensory NCS: saphenous n is abnormal

• Motor NCS: tibial, peroneal, F response, and H reflexes is normal.

• Needle EMG: VL, AL, TA, GM are abnormal

Lower lumbar plexopathy:

• Sensory NCS:  

• Motor NCS: tibial, peroneal, F responses are abnormal

• Needle EMG: 

Cramp-Fasciculation Protocol

RNS for DNMT

Tele-emg Focus

http://jnnp.bmj.com/content/76/suppl_2/ii32.full.pdf+html

Carpal tunnel syndrome

Nerve conduction studies

• Ipsilateral median motor recording APB.  Wrist and elbow (AF) stimulation sites,  (F-wave if there is additional concern regarding a plexus or nerve root abnormality). 

• Ipsilateral ulnar recording ADM.  Wrist, BE, and AE stimulation sites, (F-wave if indicated).

• Crossover check for median/ulnar anastomosis of the forearm if amplitude or configuration changes involving either median or ulnar studies suggested need for crossover evaluation.

• Change protocol of both median and ulnar studies are abnormal (example peripheral neuropathy protocol) or if only ulnar is abnormal (evaluation for ulnar neuropathy).

• Ipsilateral median and ulnar palmar sensory studies (or alternative sensory protocol).

• Consider recording antidromically from a specific digit, the wrist thumb, if the patient has symptoms restricted to either an individual finger or thumb.

• If both ulnar and median sensory latencies are abnormal, consider radial sensory for comparison.

• Temperature recheck if all sensory distal latencies are prolonged.

• Again, consider changing protocol if there are multiple sensory abnormalities (that is sensory neuropathy evaluation).

• Contralateral median sensory, lateral median sensory latency is abnormal or if symptoms are bilateral.

Needle examination

• If the clinical history, physical examination and nerve conduction studies are consistent with a diagnosis of carpal tunnel syndrome, needle examination may not be essential to completing the examination.

• It is important to be certain that the symptoms which extend into the median nerve distribution could not be secondary to a proximal abnormality, either in the area of the pronator teres muscle, at this pronator syndrome or anterior interosseous syndrome, or more proximally in the area of the brachial plexus or at the level of the nerve root, that is radiculopathy.

• If the needle examination is carried out, it should involve the thenar muscle, possibly the opponens pollicis.  Also consider the flexor hallucis longus because of its position proximal to the carpal tunnel and its derivation from the anterior interosseous branch of the median nerve.  An additional proximal muscle, the pronator teres may be helpful because of its median nerve supply and inclusion of both C6 and C7 nerve roots.  If the differential diagnosis includes a question of C6 radiculopathy additional proximal muscles with C6 innervation should be examined.

• Be mindful of T1 involvement of thenar muscles and the association of decreased median motor amplitude in combination with normal median sensory studies as an indicator of the lower trunk or T1 related pathology.

Tarsal Tunnel Syndrome

The recommendations are based upon the assumption that the clinical situation, as evaluated through the history and physical examination and testing, including other NCSs and needle EMG examination, has excluded the possibility of polyneuropathy, radiculopathy, and other conditions that might be responsible for the patient’s symptoms. The following EDX tests are recommended for confirming the presence of tibial mononeuropathy at the level of the tarsal tunnel in the ankle/foot in patients with clinically suspected TTS:

1. Tibial motor NCSs, with responses recorded over the abductor hallucis and abductor digiti minimi pedis muscles, demonstrating prolonged distal onset latency (Level C, Class III).

2. Medial and lateral plantar mixed NCSs, demonstrating prolonged peak latency or slowed conduction velocity across the tarsal tunnel (Level C, Class III).

3. Medial and lateral plantar sensory NCSs, demonstrating slowed conduction velocities across the tarsal tunnel and/or small amplitude or absent responses (Level C, Class III).

4. The utility of needle EMG in the assessment of TTS is unclear (Level U, data insufficient).

Recommended Nerve Conduction Study Protocol for Tarsal Tunnel Syndrome

Routine studies:

1. Distal tibial motor (medial and lateral plantar) studies, stimulating tibial nerve at medial malleolus and recording abductor hallucis brevis (medial plantar) and abductor digiti quinti pedis (lateral plantar).  Comparison with contralateral side is required.

2. Routine tibial motor study, recording abductor hallucis brevis, stimulating medial ankle and popliteal fossa

3. Routine peroneal motor study, recording extensor digitorum brevis and stimulating ankle, below fibular neck, and lateral popliteal fossa

4. Medial and lateral plantar mixed or sensory studies (plantar mixed and sensory responses usually require averaging several potentials). For mixed studies, stimulate medial sole and record medial ankle (medial plantar mixed); stimulate lateral sole and record medial ankle (lateral plantar mixed).  For sensory studies, stimulate great toe and record medial ankle (medial plantar sensory); stimulate little toe and record medial ankle (lateral plantar sensory). Comparison with the contralateral side is required, using identical distances between the stimulating and recording sites

5. Sural sensory response, stimulating posterior calf, recording posterior ankle

6. Tibial and peroneal F responses.

7. H reflexes, bilateral studies (may be abnormal in S1 radiculopathy or polyneuropathy but not in tarsal tunnel syndrome)

From a practical point of view, it is nearly impossible to diagnose tarsal tunnel syndrome in the presence of a polyneuropathy.

Recommended Electromyographic Protocol for Tarsal Tunnel Syndrome Routine muscles:

1. Abductor hallucis brevis and abductor digiti quinti pedis (must be compared with the contralateral side) 

2. At least two distal tibial-innervated muscles proximal to the tarsal tunnel (e.g., medial gastrocnemius, soleus, tibialis posterior, flexor digitorum longus)

3. At least one distal peroneal-innervated muscle in the lower leg (tibialis anterior, extensor hallucis longus)

Special considerations:

• If any muscle proximal to the tarsal tunnel is abnormal, additional muscles must be sampled to determine whether the lesion represents a more proximal tibial or sciatic neuropathy, lumbosacral plexopathy, radiculopathy, or polyneuropathy.

• From a practical point of view, it is nearly impossible to diagnose tarsal tunnel syndrome in the presence of a polyneuropathy.

• Examination of intrinsic foot muscles often is painful for patients and these muscles are difficult to activate. Increased insertional activity and occasionally fibrillation potentials, associated with large, long duration motor unit action potentials, are frequently found in normal subjects without symptoms.  Interpreting the electromyographic findings in an intrinsic foot muscle as abnormal requires that the abnormalities be fairly marked or the contralateral asymptomatic muscle is distinctly different on EMG from the symptomatic side.

CIM vs CIP

Direct muscle stimulation is performed by placing a monopolar needle stimulating electrode (as the cathode) in the distal third of the muscle with a nearby subdermal needle electrode placed laterally as the anode.  The muscle is stimulated using a 0.1 ms duration stimulus, gradually increasing current from 10–100 mA until a clear twitch is felt or seen.  Based on where the twitch is seen, another subdermal needle electrode (active recording electrode) is placed 1–3 cm from the stimulation electrode, with a surface electrode placed several centimeters distally as the reference electrode.  During stimulation, both the stimulating monopolar needle electrode and the active recording subdermal needle electrode can be adjusted to optimize the response at low levels of stimulation intensity.  The stimulation intensity is increased until a maximal response, the direct muscle action potential (dmCMAP), is obtained.  Next, using the same recording electrode montage, the nerve to the muscle is stimulated in the usual manner to obtain a nerve-evoked compound muscle action potential (neCMAP). The dmCMAP is compared with the neCMAP.  In CIM, the neCMAP/dmCMAP ratio is close to one, because both amplitudes are proportionally reduced.  In CIP, the ratio is much lower and may be zero because of the disproportionately lower neCMAP compared with the dmCMAP.

SET and LET

Prior to the SET and LET, routine EMG/NCS is performed. 

Short exercise test: useful in non-dystrophic myotonias, Paramyotonia congenita and Myotonia congenita.  It shows decrement in PC and MC.

1. Immobilize hand and forearm.

2. Maintain limb temperature 32-34° C

3. Record supramaximal CMAP at ADM stimulating the ulnar nerve at wrist with muscle at rest to ensure that the baseline CMAP is stable.

4. Have the patient perform maximal voluntary contraction (isometrically) for 10 seconds.

5. Record supramaximal CMAP at ADM stimulating ulnar nerve at wrist post-exercise, immediately . 

6. Six additional single stimuli every 8 seconds are delivered over the course of next 50 seconds. 

7. Sequence (post-exercise): 2 s > 10 s > 18 s > 26 s > 34 s > 42 s > 50 s. 

8. After 10 seconds rest, perform 2 subsequent identical trials each preceded by 10 seconds of isometric exercise. 

Total: 3 trials.  

Baseline CMAP from initial trial is referenced – same stimulus intensity is used.

Each trial has total of 7 stimuli: immediate (2s) followed by 6 additional stimuli

SET with cooling:

1. Same algorithm as above

Cooling is delivered for 7 minutes with a target cutaneous temperature of 15 degree centigrade.  In normal individuals, cooling with or without rewarming the limb does not alter the normal pattern. 

Long Exercise Test: McManis Protocol: Useful in Periodic Paralysis, HyperKPP, HypoKPP, Andersen-Tawil Syndrome. In the long exercise test (LET) a focal attack of  paralysis is induced by exercise of a single muscle. 

1. Immobilize hand and forearm.

2. Maintain limb temperature 32-34° C

3. Record supramaximal CMAP at ADM stimulating ulnar nerve at wrist to ensure stable baseline.

4. Have the patient perform maximal voluntary contraction (isometrically) for 5 minutes, resting every 15 seconds for at least 4 seconds.

5. Have the patient relax completely after completion of 5 minutes of exercise.

6. Record CMAP immediately, then every minute for 5 minutes, and then every 5 minutes for upto 50 minutes post-exercise.

7. Decrement is calculated as = (Highest CMAP amplitude after exercise minus smallest CMAP amplitude after exercise) divided by (highest CMAP amplitude after exercise) and multiplied by 100 to get %. Any decrement of > 40% is definitely abnormal.

Repetitive Nerve Stimulation test (10 Hz and 3 Hz):  RNS is performed in suspected non-dystrophic myotonia cases only when the Edx assessment is inconclusive. 

• MC – 10 Hz, warm limb: CMAP amplitude continuously declines.

• PMC – 10 Hz, cold limb: CMAP amplitude continuously declines.

• PMC – 3 Hz, warm limb: Initial reduction in CMAP amplitude following exercise which then declines further and then gradually increases with 3 Hz stimulation.

5 patterns are seen.  The first, three utilize the SET alone.  The other 2 patterns are defined by a combination of LET and SET.

• Normal.  Slight CMAP amplitude and/or area increment immediately following exercise that rapidly returns to baseline during the 1st trial and does not differ with the 2nd and 3rd trials.  An increment of <10% or decrement of <20% in CMAP amplitude and/or area compared to baseline in considered normal. 

• Paramyotonica congenita (PMC):  type 1 pattern

  • SET: Little or no decrement in CMAP amplitude or area immediately following exercise. With the subsequent 6 stimuli the amplitude declines providing a curve with a negative slope. The magnitude of this response becomes more dramatic in the 2nd or 3rd trials. There is most dramatic response with cooling, however.  

  • SET with limb cooling, or rewarming following cooling demonstrates a CMAP amplitude or area decrement of >20% in response to cooling with or without rewarming is thought to be pathognomonic of PMC.  

  • PEMPs seen in response to single or repetitive stimuli following brief exercise – found in all PMC patients.  PEMPs dissipate within an individual trials and between subsequent SETs. 

  • LET in PMC: Significant and persistent CMAP amplitude and area decrement occurs averaging a 66% reduction in comparison to baseline.  

  • Myotonic discharges in EMG. 

  • PMC phenotype (Q270K) SET has a unique signature. SET test with cooling demonstrates type 2 pattern identical to MC (ie) an initial CMAP amplitude and/or area decrement immediately post-exercise that improves within the 1st trial and then between subsequent trials.  SET with cooling reverts to type I pattern typically seen in PMC, that is CMAP amplitude/area decrements with a downward slope within the 1st trial and declines further with each subsequent two trials. 

• Myotonic congenita (MC):

  • MC – AR (Becker disease). Type 2 pattern. 

    • SET: CMAP amplitude and area decrement is the greatest in initial response following exercise.  If decrement is >40% of baseline, CMAP amplitude, it is considered pathognomonic of a chloride channel disorder.  With the next 6 stimuli delivered over the ensuring 50 seconds, the decrement lessens and CMAP amplitude and areas gradually approach the baseline thus rendering a curve with an ascending positive slope.  With subsequent 2 trials, the magnitude of decrement lessens but the trajectory of curves remain the same. 

  • MC (AD – Thomsen).  Type 2 pattern but not as marked as the AR type of MC.

    • SET with cooling of limb: Decrement is marked in autosomal dominant MC.

  • PEMPs is seen in 1/3 of patients with MC with single or repetitive stimuli

  • Myotonic discharges on EMG is all patients with MC

  • LET in MC produces a pattern that is indistinguishable from normal controls. 

• Potassium aggravated myotonia (PAM): Type 3 pattern. 

  • SET is normal.  

  • No PEMPs.  

  • SET with cooling is normal.  

  • LET is normal.  

  • Myotonic discharges seen on EMG. 

• HyperKPP: Type 4 pattern.  Fournier et al.  

  • SET demonstrates immediate CMAP amplitude and area increment that exceeds that seen in controls both in amplitude and in duration of effect.  It persists throughout the minute of study.  With repetitive trials of SET, the CMAP amplitude and area increments in comparison to baseline by an average of 64%.  According to Tan et al. SET is normal in HyperKPP.  

  • Myotonic discharges are seen occasionally in some HyperKPP patients. 

  • PEMPs are absent.  

  • LET shows long, slow decrement.  A decrement of at least 40% of CMAP amplitude and area with LET is found in majority of periodic paralysis patients and may be seen in Anderson-Tawil syndorme. 

• HyperKPP or HypoKPP1: Type 4 or 5

• LET shows long, slow decrement.  A decrement of at least 40% of CMAP amplitude and area with LET is found in majority of periodic paralysis patients and may be seen in Anderson-Tawil syndorme. 

• HpoKPP1: type 5 pattern.  

• No myotonic discharges.  

• No PEMPs.  

• SET is normal. 

• LET shows slowly developing decremental pattern as see in type 5 pattern. 

• Mean time to reach decrement is ~25 minute but may take 50 minutes or even longer. 

LET- Normal.  Minimal initial decrement in CMAP amplitude and/or area with return to baseline. 

McManis Protocol (LET):

A long exercise study was performed on the left Abductor Digiti Quinti muscle with surface stimulation of the Ulnar nerve at the wrist. The muscle was of normal strength and the study was performed while taking daily supplemental potassium chloride. The evoked potential amplitude was 6.7mV at a temperature of 34° C. Repetitive stimulation was performed using the technique described by Mayo Clinic [McManis, et.al., Muscle and nerve 9:704, 1986]. Initial CMAP amplitude was 5.7mV to 6.7mV [average = 6.2 mV] during the 5 minutes prior to exercise. Maximum Voluntary effort was made for 5 minutes with 3 to 4 second rest periods every 15 seconds. 

There was an immediate post-activation facilitation of 68 percent. Continuing a single stimulation at that same temperature at 1 minute intervals through 56 minutes produced a progressive CMAP amplitude reduction to 3.0 mV that was maximal at 46 minutes. Specific CMAP amplitudes were 8.1 mV at 5 min, 6.3 mV at 10 min, 5.2 mV at 15 min, 4.5 mV at 20 min, 3.8 mV at 25 min, 3.4 mV at 30 min, 3.3 mV at 35 min, 3.6 mV at 40 min, 3.1 mV at 45 min, and 3.4 mV at 50 min.

Summary: The prolonged exercise test demonstrates an initial facilitatatory response and subsequent decremental response to greater than 50% of initial values.

A short exercise study was performed on the left Abductor Digiti Quinti muscle with surface stimulation of the Ulnar nerve at the wrist. The muscle was of normal strength and the study was performed while taking daily supplemental potassium chloride. The evoked potential amplitude was 5.3 mV at a temperature of 34° C. Repetitive stimulation was performed using the technique described by [Fournier, et.al., Annals of Neurology 56:650, 2004]. Maximum voluntary effort was made for 10 seconds. 

There was an immediate post-activation facilitation of 24 percent. Continuing a single stimulation at that same temperature at 5 second intervals through 40 seconds produced CMAP amplitudes ranging from 6.6 mV to 5.2 mV. The CMAP amplitude drops to slightly below baseline by the end of the study period [50 seconds total].

Summary: The short exercise test demonstrates normal parameters.

Summary:

These electrodiagnostic findings are most consistent with a primary disorder of the muscle membrane that is best characterized as a channelopathy as seen in periodic paralysis syndromes. Given his clinical response to the supplementation of potassium this may represent Hypokalemic Periodic Paralysis

Radiculopathies

The cervical radiculopathy screen

• Six muscles without paraspinal:

  • Deltoid, triceps, PT, FCR, FCU, APB.

  • Biceps, triceps, FCU, EDC, FCR, FDI.

  • Biceps, triceps, EDC, PT, FDI, APB.

  • Deltoid, biceps, triceps, PT,  FDI, EIP, FPL (my screen): 92-95%

• Six muscles with paraspinal:

  • Deltoid, triceps, PT, EDC,  FDI, APB, PSM (my screen)

  • Biceps, triceps, EDC, FDI, FCU, PSM.

  • Deltoid, triceps, EDC, FCU, FDI,  PSM

  • Biceps, triceps, FCR, PT, APB, PSM 

C5 radiculopathy involved many of the C5/6 innervated muscles but did not involve PT.

C7 radiculopathy, triceps is always involved and FCR and PT are frequently involved. 

C8 radiculopathy involves hand intrinsic and APB muscles as well as EIP,  FPL

The lumbosacral radiculopathy screen

• Six muscles without paraspinal:

  • RFEM, AT, PT, MG, SHBF, LG

  • VM, AT, MG, PT, SHBF, GM

• Six muscles with paraspinal

  • VM, AT, MG, PT, SHBF, PSM

  • AT, MG, PT, SHBF, ADDL, PSM

  • VM, AT, MG, PT,  SHBF, GM, PSM (my screen).

S1 radiculopathy involves MG, LG, SHBF, LHBF, and AH muscles.   Paraspinal muscle involvement in S1 is seen only 25% of the time. 

L5 radiculopathy involves TFL,  gluteus medius, AT, PT, and FDL.  Paraspinal muscle involvement is seen in 50% of cases.  SHBF is not involved. 

If none of the six muscles are abnormal, the examiner can be confident that there is no radiculopathy which is confirmable by needle EMG.  In this case needle EMG can be stopped after the six-muscle screen.  The patient may have a radiculopathy, however clinical findings and imaging will be necessary to make this diagnosis.  

C7 radiculopathy

NCS:  

• Sensory: median-D1, ulnar-D5, radial - snuffbox.

• Mixed: median-ulnar transcarpal

EMG: Deltoid, Biceps brachii, Triceps, PT, EDC, FCU, EIP, FDI, APB, C6-C7 paraspinal

HFH EMG PROTOCOLS

Accessory motor nerve to trapezius muscle (CN XI)

• Position: The study is performed with the patient in the seated position.

• Recording:   Active electrode is placed over the upper trapezius, 5 cm lateral to the C7 spinous process.

• Reference:  On the most lateral aspect of the spine of the scapula.

• Stimulation:  1-2 cm posterior to the posterior border of the sternocleidomastoid muscle and slightly above its midpoint in the posterior triangle of the neck.  This is a point halfway between the mastoid process and the suprasternal notch.  The anode is superior to the cathode which should be inferior.  For RNS use bar electrodes  attached to the adapter to the stimulating probe to stimulate.  For a routine study one can use regular pronged stimulating probe.

• Ground electrode:  Acromion process.

• Machine settings: Sensitivity: 1 mV/div; sweep speed 1-2 ms/div.  LFF: 2-3 Hz, HFF: 10 kHz.

• Normal values:

  • Distance:  5-8.5 cm.

  • Amplitude:  No data but compare both sides (>3-4 mV)

  • DML:  3 ms or less.  

  • CV:  Not available.

Axillary motor nerve to deltoid muscle (C5, C6 nerve roots, through upper trunk, posterior division, and posterior cord of the brachial plexus)

• Position:  This study is performed in the seated position.

• Stimulation:  Erb's point.  The cathode is placed slightly above the upper margin of the clavicle lateral to the clavicular head of the sternocleidomastoid muscle.  The anode is superomedial.

• Recording:  Active electrode is placed 1/2 way from the acromion to the insertion of the deltoid (on a line that bisected the deltoid); most prominent portion of the middle deltoid.  Abduct the shoulder to determine the greatest muscle mass on which the active electrode is placed. 

• Reference: Placed over the junction of the deltoid muscle and its tendon of insertion. 

• Ground: Acromion process.

• Machine settings:  Sensitivity: 5 mV/div, LFF: 2-3 Hz, HFF: 10 kHz, sweep speed: 2 ms/div.

• Normal values:

  • Distance: Not standard.

  • Amplitude: 

    • 4 mV or higher for age less than 60 years.  

    • 3 mV or higher for age more than 60 years.

  • DML: 

    • 4.8 ms or less for age less than 60 years.  

    • 5.0 ms or less for age more than 60 years.

    • Duration of negative phase: 6.3 - 11.7 msec.

    • NCV: Not calculated.

    • The upper limit of normal increase in latency from one side to the other is 0.5 msec

    • The upper limit of normal decrease in CMAP from one side to the other is 54%.

F waves (Median, ulnar, peroneal and tibial nerves).

• Stimulation:  Anode is placed distal to the cathode at the most distal site of the stimulation of the motor study. 

• Recording:  Placed similar to motor nerve conduction study protocol.

• Ground:  Placed as per motor nerve protocol. 

Notes at least 16 F waves should be obtained.  If there is slowing of the NCV, a prolonged distal latency, or a prolonged F latency..  Calculate F estimate (see below).

Normal values:

• Median nerve:  Latency 31 ms or less.  Maximum side-to-side difference 3 ms or less.  

• Ulnar nerve: Latency 32 ms or less.  Maximum side-to-side 3 ms or less. 

• Fibular nerve: Latency 56 milliseconds or less.  Maximum side-to-side 4 ms or less. 

• Tibial nerve:  Latency 58 ms or less.  Maximum side-to-side:  4 ms or less

Same limb comparisons

• Nerves: Median-ulnar: Latency difference 2.4 milliseconds or less.

• Fibular-tibial:  Latency difference 4.1 milliseconds or less.

Persistence: 

• Nerve:  Tibial to foot AH: 100%

• Median to APB:  70-80%. 

• Fibular to ED be:  50s to 60%

F estimate:  If conduction velocity is slow, distal latencies markedly prolonged, or both, an F estimate can be calculated.  

• F estimate = (2D / CV) × 10 + 1 ms + DL  where D is the distance from the stimulation site to the spinal cord (cm), CV is the conduction velocity (m/s), DL is the distal motor latency (ms), and 10 is the conversion factor to ms. The turnaround time of 1 ms at the anterior horn cell is added to the equation.

• Axonal length is measured as the distance from the cathode to the distal end of the xiphoid for the fibular and tibial nerves and from the cathode to the sternal notch with the arm abducted to 90° from the median and ulnar nerves

Difference between the actual and estimated F wave latencies

• Median nerve:  +4 ms.

• Ulnar nerve:  +5 milliseconds

• Fibular nerve:  +3 milliseconds

• Tibial nerve:  +5 milliseconds

Facial motor nerve

• Stimulation:  Cathode was placed just anterior to the mastoid and just beneath the tip of the earlobe overlying the facial nerve as it exits the stylomastoid foramen.  The anode is usually inferior but often needs to be rotated to reduce shock artifact to eliminate masseter contraction.

• Recording:  Active electrode is just lateral and 1 cm of the nares, inferior to the pupil.  References in the same position on the opposite nasalis muscle.

• Ground:  On the tip of the mandible

These sites can be used for determining CMAP asymmetries etc.

Orbicularis oculi muscle recording site is preferred in this lab for the determination of facial nerve distal latencies and the facial nerve CMAP.  

• Active electrode is placed just inferior to the lateral canthus.

• Reference electrode is on the tip of the nose.

Frontalis:  

• Active electrode is midway between the eyebrow and the hairline in the pupillary line.  

• Reference electrode is placed on the opposite frontalis.  

Normal values: 

• Nasalis muscle distance: 8-14 cm, amplitude 1.8 mV or higher, distal motor latency 4 ms or less.

• Orbicularis oculi.  No standard distance.  Amplitude is 1.2 +0.7 mV distal latency 4.1 millisecond or less side-to-side difference 0.6 ms or less.

No data available for frontalis compared both sides.

Femoral motor nerve (rectus femoris vastus medialis.  

In some cases it may be desirable to obtain 2 point stimulation of the femoral nerve (e.g. to obtain an NCV or to demonstrate conduction block) in these instances the Johnson method should be used.

• Stimulation:  

  • Cathode is pushed into femoral triangle just lateral to the femoral pulse.  If a monopolar stimulator is used, the anode is placed on the lateral aspect of the upper thigh

  • Johnson:  In Hunter's canal at the inguinal ligament as above.

  • Recording:  Active is placed on the center of the rectus femoris halfway between the inguinal ligament and the patella.  References on the tendon just proximal to the patellar tendon.

  • Ground: Between the stimulating and recording electrodes.  

  • Johnston:  Active on the center of vastus medialis, reference at the patella.

Normal values:

• No standard distance.  

• Amplitude 3 mV or more.  

• DML: 6.5 ms or less.

Recommended Nerve Conduction Protocol for Femoral Neuropathy:

• Routine studies: 

  • 1. Femoral motor study recording rectus femoris, stimulating the femoral nerve below the inguinal ligament; bilateral studies.

  • 2. Saphenous sensory studies, recording medial ankle and stimulating the medial calf; bilateral studies.

  • To exclude a more generalized plexopathy or polyneuropathy: 

    • 1. Ipsilateral tibial motor study, recording abductor hallucis brevis, stimulating medial ankle and popliteal fossa

    • 2. Ipsilateral peroneal motor study, recording extensor digitorum brevis, stimulating ankle, below fibular neck, and lateral popliteal fossa 

    • 3. Ipsilateral tibial and peroneal F responses

    • 4. Ipsilateral sural sensory response, recording posterior ankle, and stimulating calf.

Recommended Electromyographic Protocol for Femoral Neuropathy:

• Routine muscles: 

  • 1. At least two heads of the quadriceps (vastus lateralis, vastus medialis, or rectus femoris)

  • 2. Iliacus

  • 3. At least one obturator-innervated adductor muscle (adductor longus or brevis)

  • 4. Tibialis anterior 

  • 5. L2, L3, and L4 paraspinal muscles

  • 6. At least two non-femoral and non-L2–L4-innervated muscles to exclude a more generalized process (e.g., medial gastrocnemius, tibialis posterior, biceps femoris, gluteus maximus)

Special considerations:

• If any of the previously mentioned muscles are equivocal, comparison to the contralateral side is useful.

• If the lesion is purely demyelinating, the only abnormality on needle electromyography will be decreased recruitment of normal configuration motor unit action potentials in weak muscles.

Greater auricular sensory nerve (C2 and C3 nerve roots)

• Position: The study is performed with the patient in the seated position.

• Recording electrode:  On the back of the earlobe.  The active recording electrode is placed inferior to the reference electrode

• Reference electrode: 2 cm distal to the active electrode.  It is placed superior on the back of the ear.

• Stimulation:  The cathode is placed against the lateral border of the sternocleidomastoid muscle, 8 cm from the active recording electrode.  The cathode is placed superior and the anode is inferior.  

• Stimulus duration should be 0.05 milliseconds.  

• Ground:  Between the stimulating and recording electrodes towards the back of the neck.

Normal values:

• Distance is 8 cm.

• Amplitude:  4.5 microvolts or above.

• Peak latency:  2.1 ms or less.

• NCV: No data.

Hypoglossal motor nerve (CN XII)

• Stimulation:  1 cm medial and 1 cm anterior to the angle of the jaw.

• Recording:  The patient is sitting with the active electrode on the tongue with the mouth closed.  The reference electrodes placed on the bony tip of the mandible in the midline.

• Ground anterolateral aspect of the neck inferior to the mandible.  

Normal values

• No distance data.

• Amplitude:  6.3 +/-2 .7 mV

• Latency:  2.4 ms or less

Notes:  Amplitude is peak to peak, waveforms are usually triphasic patient is with pacemakers or carotid sinus syndrome should not be tested.

Lateral antebrachial cutaneous sensory nerve

• Stimulation: Just lateral to the biceps tendon at the level of the elbow.

• Recording:  The active electrodes are placed 12 cm distal to the cathode along the line connecting this point with the radial pulse at the wrist.  

• Reference:  3-4 cm distal to the active electrode.

• Ground: Between the stimulating and recording electrodes.  

• Use a bar recording electrodes (usable) or disposable Natus electrodes. 

• Normal values:

  • Distances 12 cm.  

  • Amplitude is 9.6 microvolts or above.

  • Peak latency:  2.5 ms or less.

  • NCV: no data.

Medial antebrachial cutaneous nerve

• Stimulation:  Just medial to the brachial artery 4 cms above the midpoint between the medial epicondyle and biceps tendon.

• Ground:  Between the stimulating and recording electrodes.

• Recording:  Active electrode is placed 12 cm from the midpoint of the stimulation on an imaginary line that connects the ulnar styloid.  

• Reference:  Placed 3-4 cm distal to the active along the same line.

• Use a bar recording electrodes (usable) or disposable Natus electrodes. 

• Normal values:

  • Distances 8-13 cm.

  • Amplitude is 10 microvolts or above.

  • Peak latency is 2.6 milliseconds or less

Median motor nerve

• Stimulation sites:

  • Distal (wrist) stimulation site:  Cathode is 2 cm proximal to the distal wrist crease on the volar surface of the wrist between the tendons of flexor carpi radialis and palmaris longus muscles at a distance of 8 cm from the active electrode.  Anode should be proximal slightly off the nerve, away from the ulnar nerve.

  • Proximal (elbow/AF) stimulation site: Cathode is placed between the biceps tendon and medial epicondyle of the brachial artery.  Anode is proximal, rotated away from the ulnar nerve.

  • More proximal (above elbow) site:  Nerve may also be stimulated higher in upper arm at a distance of 10 cm proximal to elbow site but here it is difficult to avoid stimulating the ulnar nerve simultaneously.

• Ground:  On the dorsum of the wrist.

• Recording:  Active electrode is placed over the belly of the abductor pollicis brevis muscle at 1/3rd of the distance from the carpo-metacarpal joint to the metacarpal phalangeal joint.  

• Reference:  Placed distal to the metacarpophalangeal joint on the lateral surface of the thumb.  

• Normal:

  • Distance: 8 cm.  

  • Amplitude: 4 mV or more for ages 16-65.

  • Latency:  4.5 milliseconds or less for age 16-65.

  • NCV: 48 m/sec or more.

Notes:  Median DML should not be more than 1.8 ms greater than ulnar DML  Difference between arms should not exceed: NCV : 5 m/sec, amplitude: 10 mV.  Temperature should be maintained above 31.5° C.

Ulnar Motor Nerve - ADM muscle

• Position:  The arm is abducted 90° at shoulder joint and flexed 45° at elbow joint with the forearm supinated (palm up).

• Stimulation sites:

  • Distal (wrist) stimulation site:  Cathode is 8 cm proximal to active recording electrodie which is placed at ADM.  It is placed on the volar aspect of the wrist just medial to the tendon of flexor carpi ulnaris muscle.  The anode is rotated off the nerve away from the median nerve.

  • Below elbow stimulation site:  Cathode is 4 cms proximal to distal medial epicondyle.  Anode is proximal and rotated off.

  • Above elbow stimulation site:  Cathode is 10 cm proximal to the below elbow stimulation site. 

  • Axilla stimulation site:  Cathode is 10 cm proximal to above elbow stimulation site

  • Supraclavicular stimulation site:  Cathode is just lateral to the anterior scalene muscles and may need to be rotated for maximal stimulation.

  • Root stimulation site:  A monopolar needle is inserted lateral to the spinous process of the C7 vertebrae and advanced to the lamina.  A ground plate electrode is placed on the anterolateral neck and serves as the anode.  

• Ground:  On the dorsum of the wrist. 

• Recording:  Active on the lateral aspect of the hypothenar muscle group halfway between the distal wrist crease and the 5th metacarpal-phalangeal join on the lateral surface of the digit.  

Notes:  On stimulation above the elbow, if the conduction velocity drops by 10 ms and the amplitude drops by 20% relative to the values obtained for conduction velocity and amplitude, respectively on stimulation below the elbow site, a focal area of slowing or conduction block is demonstrated.  It becomes necessary to "inch" across the region (typically: 3 below the elbow and 4 above the elbow with the ME site as the reference (BE-BE-BE-medial epicondyle-AE-AE-AE).  This is to precisely localize the region of the conduction block. 

Ulnar inching studies:  These studies involve stimulation of the ulnar nerve at 2 cm increments across the elbow.  Inching across the region (typically: 3 points below the elbow and 3 points above the elbow with the ME site as the reference (BE-BE-BE-medial epicondyle-AE-AE-AE).  This is to precisely localize the region of the conduction block. Latency differences exceeding 0.7 ms or amplitude difference exceeding 10% are suggestive of a focal lesion.  It is preferable to see both latency and amplitude changes, as well as changes in morphology, to be certain of a focal lesion.  

Normal Values:

• Distance: 8 cm (wrist stimulation site); 4 cm (BE site), 10 cm (AE site)

• Amplitude: 7.9 mV

• DML: 3.7 ms or less

• NCV: 52 m/s (BE-wrist); 43 m/s (AE-BE or across elbow).

Notes:  

• All distances are "long" measurements; that is, they attempt to accurately follow the course of the ulnar nerve from the point of stimulation at the wrist to the point of proximal stimulation.  This means the measuring tape should make an acute turn at the elbow as it approximates the cubital tunnel.  

• Normal amplitude difference across elbow <10%.  Normal amplitude difference between elbow and wrist <20%.  Normal difference in NCV between above and elbow wrist segments is 8 m/s.  Normal difference between arms is <7 m/s, <5 mV.   Normals for patients age 22-69.

Mayo Clinic EMG lab. 

Ulnar motor nerve recording to FDI

• Stimulation:  Cathode at the distal wrist crease over the ulnar nerve.  Anode is placed proximal.

• Ground:  Dorsum of the wrist.

• Recording: Active is just distal to the 'V' made by the apposition of the fist and second metacarpals over the most fleshy part of the muscle belly.

• Reference:  Over the 1st MCP joint or 1nd MCP (can result in a positive dip).

• Normal values:

  • Distance: not noted.  Curve the tape from the site of recording and across the palm to the wrist.

  • Amplitude: 6 mV or higher

  • DML: 4.5 ms or lower

  • NCV: -

Radial motor nerve to Extensor digitorum communis (EDC)

• Stimulation sites:

  • Distal stimulation site:  Cathode is placed between the biceps tendon and the brachioradialis muscle at distance of 8 cm proximal to the active recording electrode.

  • Proximal stimulation site:  Cathode is placed at the upper lateral aspect of the arm at the border of the triceps and the lower border of the deltoid muscle.  The nerve may also be stimulated high in the axilla, just medial to the triceps and at Erb's point.  If conduction block is demonstrated between the axilla and elbow, the nerve can be "inched" across the spiral groove.

  • Recording:   Active is over the belly of the EDC muscle 10 cm distal to the lateral epicondyle.  Reference is on the dorsum of the wrist. 

  • Reference:  Dorsum of wrist. 

  • Ground:  Between active electrode and lateral epicondyle. 

  • Normal values:

    • Distance:  8 cm.

    • Amplitude: >6 mV

    • DML:  3.1 ms or less

    • NCV: >50 m/s

Ulnar sensory Nerve

Stimulation

• Antiddromic:

  • Distal stimulation site:  Cathode is  placed 14 cm proximal to active recording electrode.  It is placed on the volar aspect of the wrist just medial to the tendon of FCU muscle.  

  • Proximal stimulation site:  Cathode is placed just below the ulnar groove at the elbow.  Arm is in the position as in the motor study: The arm is abducted 90° at shoulder joint and flexed 45° at elbow joint with the forearm supinated (palm up).

• Orthodromic:

  • Palmar:  Cathode is at the palmar crease at the 4th MCP interspace (crescent palmar crease).

• Ground:  In the palm for antidromic studies, on the dorsum of the wrist for palmar studies.  

• Recording:

  • Antidromic:  Active is a ring electrode on the proximal phalanx of the fifth digit.  Reference: Also a ring electrode, placed 4 cm distal to the active electrode.  

  • Palmar:  Active is a disc electrode (bar electrode) placed 8 cm proximal to the cathode, placed on the volar surface of the wrist, just radial to the tendon of the FCU muscle. 

  • Reference:  3-4 cm proximal to this.  

• Normal Values:

  • Antidromic:

    • Distance: 14 cm

    • Amplitude: 10 microvolt

    • Peak latency: >4.0 ms

    • NCV: 55 m/s

  • Orthodromic:

    • Distance: 8 cm

    • Amplitude:  15 microvolt

    • Latency: <2.4 ms

Dorsal cutaneous branch of the ulnar nerve

• Positon: Arm supinated

• Stimulation:  The cathode is placed 5 cm proximal to the ulnar styloid between the flexor carpi ulnaris and the ulna.

• Recording: The active electrode is placed at the apex of the V between the 4th and 5th metacarpals.  The reference is placed distally at the base of the 5th metacarpal.  

• Ground:  Between the stimulating and recording electrodes.

Normal values:

Distance:  10 cm.  

Amplitude:  5 microvolts or above.  

Latency:  2.9 m/sec or less

NCV: Not calculated.  

Posterior Antebrachial Cutaneous sensory nerve

• Stimulation:  Cathode is placed just above the lateral epicondyle between the biceps and triceps muscles.

• Recording:  Active electrode is placed 12 cm distal to the point of stimulation along a line from this point to a point on the dorsum of the wrist halfway between the radial and ulnar styloids.  

• Reference:  4 cms distal to recording electrode

• Ground:  Between stimulator and the recording electrodes.

• Normal values:

  • Distance: 12 cm

  • Amplitude: >5 microvolt

  • Peak latencies: <2.9 ms

  • NCV: -

Sural Sensory Nerve

• Stimulation:  It may be at one or more of three points designated: 'A', 'B',  and 'C'.  Point A is 7 cm proximal to the active recording electrode.  B is 14 cm (standard).  C is 21 cm.  Routinely, point B is stimulated only.  If CV is required points A and C are obtained and the velocity of C-A segment is calculated.  Also, if no response is obtained at B, a low but demonstrable response at A shows that the "NR" at B was not due to technical problems. 

• Ground:  Placed between the stimulating and recording electrodes.

• Recording:  Active electrode is placed immediately behind the lateral malleolus and the reference is 4 cm distal to it.  

• Normal Values for point B stimulation site:

  • Distance: 14 cm

  • Amplitude:  4 microvolt

  • Peak latency: <4.5 ms

  • NCV: >43 m/s (C-A segment)

Notes: Over the age of 60 years it may be anticipated for the response at B to be absent.

Fibular motor nerve-EDB and to TA muscles

• Stimulation:

  • Ankle stimulation site:  Cathode is placed on the anterior aspect of the ankle between EHL and EDL tendons at a distance of 8 cm from the active electrode.

  • Fibular neck stimulation site:  Cathode is placed at the fibular neck  (just below the prominence of the fibular head).  

  • Above fibular neck/above knee:  Cathode is placed at a distance of 10 cm proximal to the fibular neck stimulation site (below-knee site), in the lateral popliteal fossa (just medial to the tendon of long-head of biceps femoris muscle).  

  • Behind Lateral malleolus stimulation site:  In the presence of an accessory peroneal nerve (a higher EDB CMAP amplitude is obtained with stimulation of the fibular neck stimulation site than at then ankle stimulation site), the nerve should be stimulated behind the lateral malleolus.

  • Ground:  

    • Fibular nerve - EDB:  On the dorsum of the foot.

    • Fibular nerve - TA:  Just distal to the tibial tubercle.

• Recording:  

  • EDB:  Active over the most prominent portion of the belly of the EDB.   Reference:  Distal at the base of the 5th metatarsophalangeal joint.

  • Tibialis anterior:  Active on the most prominent belly of TA muscle, at a distance of 9 cms from cathode.  Reference: on the anterior surface of the ankle at the level of the malleoli.  Other technique that is also used is to place the reference electrode over the medial aspect of the patella (proximal to active electrode).

• Normal values in recording at EDB.

  • Distance: 8 cm proximal to active electrode.

  • For age less than 49 years: 

    • Amplitude: 3 mV or up.  

    • Latency: 5.5 m/sec or less.  

    • NCV 41 m/sec or more.

  • For age more than 50 years:

    • Amplitude: 2.5 mV or up.

    • Latency : 6 m/sec or less.  

    • NCV 40 m/sec or more.

• Normal values in recording at TA.  

  • Distance: No standard distance. 9 cms from active recording electrode for distal stimulation at fibular head.  10 cm for proximal (above knee) stimulation site (lateral popliteal fossa, just medial to tendon of long-head of biceps femoris muscle) 

  • For age less than 49 years:

    • Amplitude 4 mV.

    •  Latency: 4 m/sec or less.  

    • NCV: 40 m/sec.

  • For age more than 50: 

    • Amplitude 3 mV or up.  

    • Latency: 4.5 m/sec or less.  

    • NCV 40 m/sec or more.

All distances from ED B stimulation are from the ankle.  For anterior tibialis muscle stimulation,  distances are from the fibular head while conduction velocities is from the knees to fibular heads segments.  Normally, using long distances from the ankle, the conduction in the knee ankle segment maybe as much as 8 m/sec slower than the fibular head segment.  The normal amplitude difference from the knee and ankle stimulation may be up to 22%.

Tibial Motor Nerve to AH muscle 

• Stimulation:

  • Distal: Cathode is placed 8 cm proximal to active recording electrode.  It is placed above the medial malleolus.  Anode is proximal to cathode. 

  • Proximal: Popliteal fossa.  Patient can semiflex the knee.  May need high stimulus amplitude.  Expected to have amplitude of upto 50% less than distal stimulation site. 

• Recording: Active electrode is placed 1 cm behind and 1 cm below the navicular tubercle at a distance of 8 cm from the cathode.  

• Reference: is placed on the medial surface of the foot on the 1st MCP joint.

• Ground: Placed on the dorsum of the foot. 

  • Normal values:

    • Distance: 8 cm

    • Amplitude: 4.4 mV

    • DML: <6.1 ms

    • NCV: 39 m/s or up

Tibial Motor Nerve to ADM (pedis) muscle 

• Stimulation:

  • Distal: Cathode is placed 19 cm proximal to active recording electrode.  It is placed above the medial malleolus.  Anode is proximal to cathode. 

• Recording: Active electrode is placed 3 cm proximal to the 5th MTP joint.  

• Reference: is placed on the lateral surface of the 5th MTP joint.

• Ground: Placed on the dorsum of the foot. 

  • Normal values:

    • Distance: 19 cm

    • Amplitude: 1.4 mV

    • DML: <8.3 ms

    • NCV: -

Notes:  Measurement of distance from ADM (pedis) a.k.a ADQ (pedis) is with tape following anatomic course of nerve.

Superficial fibular sensory nerve

• Stimulation Site:  14 cm proximal to the active electrode on lateral calf, just anterior to the fibular border.

• Ground: Between the stimulating and recording electrodes.  

• Recording: Active electrode displaced 2-3 cm proximal to the bimalleolar wine between the tibia and the lateral malleolus.

• References placed 4 cm distal to it.

• Normal values:

  • Distance:  14 cm.

  • Amplitude :> 4 microvolts.  

  • Peak latency:  4.2 ms or less.  

  • NCV:

Notes:  It may normally be absent in patients over the age of 55 years, amplitudes are measured peak to peak.  Always check the contralateral side unless super normal.

Tibial mixed nerve (Medial and Lateral plantar branches)

• Position:  Patient in supine position with knee semiflexed and leg laterally rotated.  The examiner and machine are positioned at the foot of the bed. 

• Stimulation

  • Medial Plantar nerve:  Cathode is placed on the medial edge of the plantar fascia about 2 cm distal to the navicular head.  The cathode is placed 14 cm from the active electrode.  Measure 10 cm from the recording active electrode to the glabrous interspace between the 1st and 2nd metatarsals, and then 4 cm distally.  Patient should feel the stimulation in the first or second toes.

  • Lateral Plantar nerve:  Cathode is placed 3 cm lateral to the position used for the medial plantar, between the 4th and 5th metatarsals.  Cathode is 14 cm from the active electrode.  Patient should feel stimulation in the 4th and 5th toes.  

• Recording:  The active recording electrode should be 1 cm distal to the prominence of the medial malleolus or just proximal to the flexor retinaculum (proximal to a line from the posterior calcaneum to the medial malleolus).   Bar electrode is used and is taped firmly with silk tape or velcro. 

• Reference:  4 cm proximal to active electrode

• Ground:  Between the stimulating and the recording electrodes or placed over the dorsum of foot. 

• Machine settings:  Sensitivity: 5-10 uV/div, sweep speed: 1 ms/div.  LFF: 32 Hz.  HFF: 3.2 kHz.

• Normal values for medial plantar:

  • Distance: 14 cm

  • Amplitude: 7 microvolts or higher

  • Latencies: 3.9 ms or lower

• Normal values for lateral plantar:

  • Distance: 14 cm

  • Amplitude: 3 microvolts or higher

• Latencies: 4.5 ms or lower

Notes:  

• Although technically a mixed nerve study, the technique approximates a sensory study.

• Firm pressure should be exerted on the stimulating and recording electrodes.

• Stimulus artifact may interfere with the recording, especially in persons with thick plantar skin.  Prepping the skin can be helpful.  

• Responses is often difficult to obtain even in normal subjects.  Unevokable responses must be interpreted with caution.

• After the age of 54 years, responses may not be evokable.  

• Measuring tape should follow course of tibial/plantar nerves.  

• Tarsal tunnel syndrome can be difficult to diagnose clinically and electrophysiologic corroboration is important.  Conventional electrodiagnostic techniques are insensitive; motor latency abnormalities exist in only 52%; sensory responses are frequently absent (a non-localizing finding(.

Saphenous nerve

• Stimulation: 

  • Distal:  The cathode is placed 14 cm proximal to the active recording electrode.  It is placed on the medial border of the tibia, firm pressure is required between the tibia and the medial gastrocnemius muscle.

  • Proximal:  The cathode is placed on the medial surface of the slightly flexed knee, between the tendons of the gracilis and sartorius muscles.

• Recording: 

  • Distal:  Active electrodes placed just anterior to the anterior border of the medial malleolus.  

  • Reference electrode is 4 cm distal to this.

• Normal values (distal method):

  • Distance: 14 cm

  • Amplitude 2 microvolts or higher.

  • Peak latencies: <4.4 ms.

Lateral femoral cutaneous nerve.

• Stimulation: The stimulating electrode is a monopolar needle electrode with a 3 mm bare tip inserted 1 cm superior and 1 cm medial to the anterior superior iliac spine.  The catheter is a “ground“ plate or large disc electrode placed superior to the stimulating electrode.

• Ground is between the stimulating and recording electrodes.

• Recording.  The active electrode displaced 12 cm distal to the anterior superior iliac spine along the line connecting the structure to the lateral aspect of the patella.

• Normal values:

  • Distances 12 cm.  

  • Amplitude is 10 microvolts or above.  

  • Latency: 3 milliseconds or less

Median H-reflex at FCR.  

Stimulation:  Katherine at elbow over median nerve.  Patient is supine with the elbow slightly flexed.  Stimulation duration is 500-1000 micro seconds.

Ground is between the stimulator and recording electrodes.

Recording is active electrodes over the belly of the FCR, 1/3 of the way from the medial epicondyle to the radial styloid.  References placed on the brachioradialis

Normal values:

H reflex:  Amplitude is 0.8 mV or up.  Latency is 18 minute latency difference between arms 0.4 +/-0 0.3 m/sec.

M:  Amplitude is 2.6 mV or up.  Latency is 4 m/sec or less.

Notes: Amplitudes are measured from baseline to negative peak.  An H-reflex must be obtained without an M response, or with only very small M response preceding it.  It is latency musk shortened with proximal stimulation, and its amplitude muscle degrees with increasing stimulation frequency.

Suggested protocol for electrodiagnosis of carpal tunnel syndrome (CTS).

Techs may perform the following nerve conduction studies before the doctor evaluates the patient:

In the more symptomatic/dominant upper extremity:

1.  Median sensory

2.  Ulnar sensory

3.  Median and ulnar sensory comparison to 4th finger if median sensory normal.

4.  Median motor (wrist and elbow)

5.  Ulnar motor (wrist, below and above elbow using short distances)

If symptoms in both hands, do the following on the other side:

6.  Median sensory

7.  Median and ulnar sensory comparison to 4th finger if median sensory normal.

8.  Median motor (wrist only).  Elbow stim if median DML prolonged.

Resident physician /EMG staff to evaluate the patient before proceeding further.

If NCs suggestive of CTS: proceed with the needle examination.

Suggested muscles in the more symptomatic extremity. (At least 5 muscles to get a C5-T1 innervation screen):

FDI, APB, FPL (if APB abnormal), FCR or PRT, triceps and biceps. Check deltoid and infraspinatus (if biceps abnormal).  Check cervical paraspinals if suspecting cervical radiculopathy.

Needle examination of the contralateral extremity only if there is NC evidence of CTS and median M amplitude is reduced or there is suspicion of other bilateral pathology.

If above NCs negative for CTS but the patient’s history and neurological examination is highly suggestive of CTS, complete the two other median nerve comparison studies and get a CSI (combined sensory index).

Don’t do CSI for non-specific/musculoskeletal upper extremity symptoms unless CTS suspected clinically.

Don’t do radial sensory on every patient.  Radial sensory is of value if brachial plexopathy is suspected and to get a radial/sural amplitude ratio in mild axonal peripheral neuropathy.

If a co-existent peripheral polyneuropathy is suspected additional nerve conductions (radial and sural sensory and peroneal motor) may need to be performed.

References:

AANEM Practice Parameter for Electrodiagnostic studies in CTS: Summary statement.  Muscle & Nerve June 2002, 918-923.

AANEM monograph: Electrodiagnostic evaluation of CTS.  Muscle & Nerve 2011 44: 597-607. 

CSI  Protocol

If median sensory peak latency to D2 ≤4.0 ms, then move on to CSI.

1. Median-Radial to D1 sensory comparison:  distance 10 cm.  Range to move on in protocol: 0.2 0 - 0.6 cm.  Abnormal: ≥ 0.7 ms = CTS.

2. Median - Ulnar palmar sensory comparison: distance 8 cm.  Range to move on in protocol: 0-0.3 ms.  Abnormal: ≥ 0.4 ms = CTS

3. Median - Ulnar 4th digit sensory comparison: distance 14 cm.  Range to move on in protocol: 0.1-0.4 ms.  Abnormal : ≥ 0.5 ms = CTS

CSI: (1+2+3): Thumb-diff + palm diff + ring diff; ≥ 1.0 ms = CTS

Additional consideration: Median 2nd lumbrical - ulnar palmar interossei, motor: distance 10 cm. Abnormal: ≥ 0.5 ms.

Dr. Schwalb (Brachial Plexus Protocol)

In addition to the routine brachial plexus studies for the diagnosis, Dr. Schwalb needs the following studies for to plan brachial plexus repair: 

Nerve conduction studies: Spinal accessory, Supra-scapular, Long thoracic, Thoracodorsal, Pectoral, (sural).  Radial motor when middle or lower trunk

EMG:  Trapezius, Infraspinatus, Serratus anterior, Latissimus dorsi, Pectoralis major

Method:  The thoracodorsal nerve was stimulated at the axilla and Erb's point with recording over the latissimus dorsi.  The latency was 1.9 (range:  1.2-2.7) ms and 3.6 (range:  2.8-4.5) ms for the axillary and Erb's points stimulations, respectively.  The amplitude of the compound muscle action potential was 4.1 +/-1.8 mV on the right and 3.9 plus/minus 1.4 mV on the left.  The CMAP ratio was 0.8 plus/-0.12 (range, 0.55-0.99).  The study is useful to evaluate the integrity of the thoracodorsal nerve and to assist in the diagnosis and prognosis of brachial plexus injury.

Blink reflexes

Blink reflexes are most commonly and reliably obtained with stimulation of the supraorbital nerve (V1), but may also be obtained with stimulation of the infraorbital nerve (V2), or the mental nerve (V3).  These are branches of the trigeminal nerve (afferent).  The efferent limb of the reflex is subserved by facial nerve CN VII to the orbicularis oculi muscles, bilaterally. 

• Stimulation:

  • V 1:  Cathode is placed over supraorbital nerve as it passes through the supraorbital notch.  Anode is above and usually needs to be rotated to minimize shock artifact

  • V2:  Cathode is over the infraorbital nerve as it exits through the infraorbital foramen on the inferior rim of the orbit.  Anode is below the cathode.

  • V3:  Cathode is halfway between the angle of the mandible and the tip of the jaw with the cathode forward.  

• Ground electrode: On the chin.

• Recording electrode:  Active electrode is on the upper lateral aspect of the orbicularis oculi between the lateral canthus and the eyebrow.  

• Reference: On the tip of the nose.

Notes: The patient lies with eyes open or gently closed in a quiet room.  If no R1 can be obtained, a paired stimulus with a 5 ms interstimulus interval may be used.

• Normal values for V1 stimulation: 

  • • R1: <13 ms,  ipsilateral R2:  <40 ms.  Contralateral R2:  <41 milliseconds.  R 1/D ratio:  2.6-4.6.

Notes: Side-to-side differences should not exceed 1.2 ms for R1 and 7 ms for R2.  The difference between R2 ipsilateral and contralateral R2 latencies should be less than 5 milliseconds for one side stimulation.  R1/D ratio is ratio of R1 latency to the direct facial motor distal latency.

• Normal values for V2 stimulation:

  •  Less than 41 ms and less than 42 ms.

• Normal values for V3 stimulation

  • Less than 50 ms may not be obtainable.  Less than 51 ms.

Grading the needle exam

Insertional activity refers to the electrical activity caused by the mechanical stimulation of or damage to, muscle fibers.  It is defined as either normal, increased, or decreased. 

• Normal:  May last 300-500 ms following needle movement.  Usually "spikey."

• Slightly increased:  This is a variant of normal in which persistent insertional activity in the forms of "snaps, crackles, and pops", with an isoelectric baseline in between, may be seen for several seconds following needle movement. 

• Increased:  Last greater than 500 ms.  May consists of positive waves, spikes or combinations of these.  May be seen in diseases of nerve, muscles or in some normal variants. 

• Decreased: Little or no activity is seen or heard.  Usually, the needle moves with uncommon ease, encountering little resistance.  Alternatively, the muscle feels gritty.  These may be seen with either fatty or fibrous replacement of muscle or during an attack of periodic paralysis.  Here, however, the muscle will "feel" normal. 

Fibrillation grading: 

• 0: absence of fibrillation.

• +/-: Equivocal fibrillation.  Examples include the presence of a single run of persistent fibrillation potentials, (e.g., lasting one or two seconds), in one spot.  Alternatively, several runs of fibrillation potentials may have been seen in one side only. 

• 1+: Unequivocal persistent fibrillation.  Examples include persistent fibrillation potentials, (e.g., lasting one or two seconds), in at least tow areas of muscle.  

• 2+:  Moderate numbers of fibrillation potentials in at least three areas. 

• 3+: Large numbers of persistent fibrillation potentials in all areas.

• 4+: Profuse persistent fibrillation potentials that fill the base line in all areas. 

Fasciculation grading:

• 0:  No fasciculations seen. 

• +/-:  A single potential with the characteristics of a fasciculation was seen in one location only.

• 1+: Unequivocal evidence of fasciculations is seen in at least two spots of the muscle at rates of 2-10 per minute.

• 2+:  Unequivocal persistent fasciculations in many areas of muscle at rates of 10-15 per minute. 

• 3+: Many fasciculations seen in all areas of muscles at rates of 15-100 per minute.

• 4+:  Profuse fasciculations in all areas examined at rates of greater than 100 per minute.  

Grading MUAP

Effort is a difficult aspect of EMG to grade and is necessarily subjective.  For these purposes it is graded:

• Normal:  indicates ostensibly normal effort. 

• Reduced:  indicates that it is felt less than full effort is being given.  A useful guideline is the absence of MUPs firing at greater than 20 Hz with effort.  Realistically however, it is not possible to distinguish a slow firing rate due to poor effort or pain from one caused by an upper motor neuron lesion or a central disorder of motor control.  If the examiner feels that effort is reduced, one should explicitly add the disclaimer in the comment window that the reduced effort could be due to pain, poor effort, or a central disorder of motor control. 

Recruitment:  The recruitment of motor units is best assessed by observing the number and firing rates of MUPs with increasing effort.  Motor units in various muscles begin at 5-8 Hz.  With increasing effort those units activated begin to fire faster and more units are recruited.  With loss of either anterior horn cells or peripheral motor axons, the recruitment frequencies increase - that is, motor units fire at faster rates before additional units are recruited. It is therefore possible to estimate recruitment with mild, moderate, and /or maximal levels of effort. 

• • Normal:  The number and firing rates of MUPs is normal for the muscle. 

  • Reduced:  Recruitment may be expressed as the ratio of the rate of firing of the motor units to the number of motor units firing.  Normally, it is less than 5.  A ratio over 10 represents the loss of motor units.  For example, two units firing at 10 Hz gives a recruitment ratio (RR), of 5.  Three units firing at a rate of 30 Hz gives a RR of 10.  Reduced recruitment is grade as follows:

    • 0:  Recruitment ratio of 5 or less. 

    • +/-:  Recruitment ratio of 6 to 7.

    • 1+:  Recruitment ratio of 8 to 10.

    • 2+: Recruitment ratio of 10 or more

    • 3+:  Single unit, (discrete), activity >25 Hz, or a RR of 15 or more.

    • 4+: No MUPs.  

    • Early recruitment. 

Amplitude:  MUP amplitude, duration, and polyphasic MUPs are routinely judged at mild to moderate levels of effort, with a standard concentric needle electrode, and with filter settings of 20 Hz to 10 kHz.

• • • Grading:

      • 0:  Virtually all MUPs are within normal limits

      • +/-: ~ 10% of MUPs are larger than the normal limit for age and muscle. 

      • 1+: ~ 25% of MUPs are larger than the normal limit for age and muscle. 

      • 2+: ~50% of MUPs are larger than the normal limit of age and muscle. 

      • 3+: ~75% of MUPs are larger than the normal limit for age and muscle. 

      • 4+: Virtually all the MUPs are larger than the normal limit of age and muscle. 

Duration:

• • • +/-: ~ 10% of MUPs are longer than normal limit for age and muscle. 

    • 1+: ~25% of MUPs are longer than the normal limit for age and muscle. 

    • 2+:  ~ 50% of MUPs are longer than the normal limit of age and muscle. 

    • 3+: ~75% of MUPs are longer than the normal limit for age and muscle. 

    • 4+: Virtually all of the MUPs are longer than normal limit forage and muscle 

Polyphasic motor units:  Most muscles have about 12% polyphasic MUPS.  The deltoid and tibialis anterior muscles average about 25%.

• • • 0: Normal percentage of polyphasic MUPs for the age and muscle.

    • +/-: ~ 10% of MUPs are more polyphasic than normal limit for age and muscle. 

    • 1+: ~25% of MUPs are more polyphasic than the normal limit for age and muscle. 

    • 2+:  ~ 50% of MUPs are more polyphasic than the normal limit of age and muscle. 

    • 3+: ~75% of MUPs are more polyphasichan the normal limit for age and muscle. 

    • 4+: Virtually all of the MUPs are more polyphasic than normal limit forage and muscle 

Autonomic testing using Natus EMG machine

Phrenic nerve studies

https://musculoskeletalkey.com/pictorial-guide-to-nerve-conduction-techniques/

Teres minor nEE

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8178592/