Carpal tunnel syndrome
The incidence of CTS adjusted to the 2000 US population is 376 per 100 000 person-years and 491 and 258 per 100 000 person-years for women and men, respectively.
The lifetime prevalence of CTS among workers approximates 6.7%, with a 12-month prevalence of 3.1%.
An estimated 4.8 million workers in the United States have CTS, of which 67.1% of cases are work related.
In a study of 262 patients with symptoms suggestive of CTS, the population prevalence of numbness/tingling in the median distribution was 14.4% (95% confidence interval [CI], 13–15.8). The prevalence of clinically certain CTS (symptoms plus examination findings) was 3.8% (95% CI 3.1–4.6). The prevalence of CTS with EDX confirmation was 2.7% (CI 2.1–3.4). This study concluded that one in five symptomatic patients would be expected to have CTS on the basis of clinical examination and EDX testing and reaffirmed the relevance of EDX studies in symptom-based classification.
Carpal tunnel syndrome is often work-related, particularly in jobs with high hand/wrist exposure, and is a major cause of workers' compensation claims. Annually, more than 500 000 carpal tunnel release procedures (CTR) are performed in the United States, with an associated cost of $2 billion dollars and additional productivity losses because of CTS.
The minimum requirements for the EDX evaluation of CTS outlined in the AANEM Practice Parameters and in Clinical Quality Measures published by the Carpal Tunnel Quality Group are testing of median sensory latency, testing of median distal motor latency, another sensory and motor nerve study in the same extremity, and, if these results are normal, followed by comparison short segment studies.
Hand temperature measured and maintained during EDX testing Nerve conduction studies are susceptible to technical factors that affect the evoked responses. Low temperatures increase sensory response amplitudes and compound motor action potential duration, prolongs latencies, and reduces conduction velocities. The use of correction factors for temperature does not accurately normalize data from cool limbs. Although maintaining limb temperature throughout an EDX test is potentially time-consuming, it is necessary to avoid false positive EDX results and misdiagnosis of median neuropathy at the wrist.
Diagnosis of carpal tunnel syndrome is often based on history and physical examination, with EDX studies performed adjunctively. Electrodiagnostic testing is valuable to confirm median neuropathy at the wrist, assess the severity and evaluate axonal loss, identify conditions that coexist with or mimic CTS such as cervical radiculopathy, and investigate potential reasons for poor outcomes after CTR.
The AANEM practice parameter for EDX in CTS and the Normative Data Task Force outlines EDX studies and reference values that are considered standard of care in patients with clinical suspicion of CTS. These studies are valid and reproducible in confirming median neuropathy at the wrist with a high degree of sensitivity (>85%) and specificity (95%).
Electrodiagnostic criteria for severity of median neuropathy at the wrist are defined in the AANEM minimonograph “The Electrodiagnosis of Carpal Tunnel Syndrome.”
The severity of median neuropathy informs treatment options and prognosis. Severe axonal loss requires urgent surgery to preserve remaining function and suggests incomplete recovery after surgery.
Electrodiagnostic testing confirms the diagnosis of median neuropathy at the wrist, evaluates its severity, determines its pathophysiology (axon loss vs demyelination), and excludes cervical radiculopathy and coincidental ulnar nerve disease or polyneuropathy. In a retrospective case series, EDX testing led to identification of an alternative diagnosis (polyneuropathy, radiculopathy, motor neuron disease, spondylotic myelopathy, syringomyelia, and multiple sclerosis) in 12 patients undergoing CTR without resolution of symptoms. Review of operative EDX studies in 11 patients revealed errors in either the performance or the interpretation. This measure evaluates the proportion of patients with CTS who did not have EDX or other studies, such as MRI of the wrist, ultrasound, or other tests, prior to CTR.
Pain
Pain/paresthesiae associated with driving or holding a phone, book, or newspaper
Nocturnal paresthesias awakening patient from sleep.
Shaking or ringing the hands alleviates the paresthesiae.
Sensory disturbance of digits 1, 2, 3, and radial half of 4th digit.
Weakness/wasting of thenar eminence
Phalen's maneuver reproduces symptoms (usually in the 3rd digit) within 30 seconds to 2 minutes in CTS, and is more sensitive than Tinel's sign.
Tinel's sign over the median nerve at the wrist.
50% sensitive and 77% specific
Compare sensation over the lateral ring finger (median innervated) to that over the medial ring finer (ulnar innervated).
The neck is not affected.
Little finger is spared
Sensation over the thenar eminence is spared.
Causes:
Repetitive stress, occupational, hypothyroidism, acromegaly, diabetes, RA, ganglia, lipoma, schwannoma, neurofibroma, hemangioma, persistent median artery, congenital small tunnel, anomalous muscles (palmaris longus, FDS), sarcoid, histoplasmosis, septic arthritis, lyme, TB, Colles' fracture, H'ge, spasticity, HD, amyloidosis, pregnancy.
Mnemonic: PRAGMATIC: Pregnancy, RA, Amyloidosis, Grave's disease (thyroid disorders), gout, Multiple myeloma, mass, Abnormal anatomy, acromegaly, Tenosynovitis, Infection, Inflammation, Compression.
Sensation is spared over the thenar eminence because the palmar sensory branch that innervates the thenar eminence travels outside the carpal tunnel.
DDx: C6, C7 radiculopathy, brachial plexus, and compression of the median nerve proximal to the carpal tunnel.
EDX:
Slowing of sensory and motor conduction across carpal tunnel. Distal latency is prolonged on the median sensory study before motor NCS are abnormal. However, routine nerve conduction studies may be normal. Specific testing for focal slowing or conduction block of median nerve fibers across the carpal tunnel may be performed. For instance, the median nerve can be compared to the ulnar nerve, such as with the palmar mixed study, on inching may be performed (segmental stimulation of the median nerve across the carpal tunnel)
CTS is typically due to demyelination, but there may be secondary axonal loss.
Velocity <44m/s indicates slowing across CT
Difference in sensory distal latency of more than 0.5ms between ulnar and median indicates CTS
Decreased amplitude of SNAP and CMAP
Severity: Different grading scales are used to grade the severity of median neuropathies at the wrist - Mayo Clinic Standard:
Mild CTS: Prolonged sensory or mixed (palm-wrist) distal latency, +/- amplitude reduction
Moderately severe CTS: Prolonged sensory or mixed (palm-wrist) distal latency, +/- amplitude reduction PLUS prolonged median motor distal latency
Severe CTS: Absent sensory response OR Low amplitude CMAP
Very Severe CTS: Absent routine sensory and thenar motor responses.
Documenting an electrophysiologic grade of the degree of the median neuropathy at the wrist is useful in the EMG report, because it may guide the referring physician’s decision on treatment.
Tx: Wrist splint by maintaining wrist in a neutral position at night, surgery definitive treatment
Identification of Aberrant Muscle Bellies in the Carpal Tunnel using Sonography - PMC (nih.gov)
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.
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.