EMG carpal tunnel syndrome

Carpal tunnel syndrome

Epidemiology of CTS 

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.  

Essential components of EDX evaluation for median neuropathy at the wrist 

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.

Temperature

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. 

EDX criteria for diagnosing median neuropathy at the wrist 

EDX criteria for diagnosing severe median neuropathy at the wrist 

Preoperative EDX testing for CTS 

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. 

Clinical symptoms and signs:

Identification of Aberrant Muscle Bellies in the Carpal Tunnel using Sonography - PMC (nih.gov) 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7460039/

Carpal tunnel syndrome

Nerve conduction studies

Needle examination


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.