Electromyography in carpal tunnel syndrome

A clinician typically arrives at the diagnosis of carpal tunnel syndrome (CTS) from taking a thorough history and performing a detailed physical examination, including Tinel's and Phalen's tests which may elicit symptoms of CTS. (1)

A diagnosis of CTS would not normally warrant further investigation when symptoms are mild, and no other differential can better explain the symptoms. (2)

However, under the presence of severe symptoms such as weakness, sensory deficits, or limitations in activities of daily living, patients should undergo nerve conduction studies. (3)

Electromyography is considered a gold standard in diagnosing CTS as it provides objective, measurable information regarding the median nerve's physiologic health. However, it is not a perfect test as false positives and false negatives are well documented.(2)

• a positive test shows delay in the latency of the motor unit action potential for the abductor pollicis brevis (4)
• false negative rates for neurophysiological examination of the median nerve - estimated to be between 7 and 13%.

Reference:

1. Newington L, Harris EC, Walker-Bone K. Carpal tunnel syndrome and work. Best Pract Res Clin Rheumatol. 2015 Jun;29(3):440-53
2. Sonoo M, Menkes DL, Bland JDP, Burke D. Nerve conduction studies and EMG in carpal tunnel syndrome: Do they add value? Clin Neurophysiol Pract. 2018;3:78-88
3. Saint-Lary O, Rébois A, Mediouni Z, Descatha A. Carpal tunnel syndrome: primary care and occupational factors. Front Med (Lausanne). 2015;2:28
4. Mills KR. The basics of electromyography. J Neurol Neurosurg Psychiatry. 2005 Jun;76 Suppl 2(Suppl 2):ii32-5