Median Nerve Entrapment Workup

Updated: Mar 11, 2020
  • Author: Bardia Amirlak, MD; Chief Editor: Harris Gellman, MD  more...
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Workup

Laboratory Studies

Some evidence suggests that there is a higher prevalence of concurrent conditions, such as diabetes mellitus and rheumatoid arthritis, in patients with carpal tunnel syndrome (CTS). At present, however, there is not enough evidence to warrant routine laboratory screening for such conditions in all patients with newly diagnosed CTS. [71]

Low-value preoperative testing remains relatively common in patients undergoing carpal tunnel release and should be reduced. [72]

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Imaging Studies

Both ultrasonography (US) and magnetic resonance imaging (MRI) may be useful in the evaluation of patients with upper-extremity neuropathies. [73, 74] Atrophy can be appreciated in the involved muscles. Signal changes can also point to the affected muscles.

US can similarly identify the affected muscles by looking at the muscle mass, perfusion on Doppler US, and active contraction of affected muscles. [75, 76]  For diagnosis of CTS, peripheral nerve US may be particularly useful in combination with electrodiagnostic studies (see Procedures). [77, 78]

Sonoelastography also appears to be potentially useful for the diagnosis of CTS, in that the median nerve in CTS patients has been found to be substantially stiffer than in healthy volunteers. [79]  Ultrasound elastography may also be useful for determining the severity of CTS. [80]

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Procedures

Electrodiagnostic examination

Major limitations are associated with electrodiagnostic examination. False-positive and false-negative results are common. Patients with a positive clinical diagnosis of CTS and negative findings on electrodiagnostic studies improve with carpal tunnel release. [81]

Although electrodiagnostic studies provide quantifiable values, they are particularly dependent on the proficiency of the examiner. [82]  These studies should only complement the clinical evaluation by helping to localize the level and severity of the injury and to monitor the progression of the disease when it is being managed conservatively. Electrodiagnostic studies are not generally helpful in confirming a diagnosis of more proximal lesions.

The American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM) has development a quality measurement set for the electrodiagnosis of CTS. [83]

Needle electromyography

Needle electrodes are placed into muscle to record fibrillation potentials; sharp waves and increased insertional activity indicate advanced nerve compression. However, electromyography (EMG) cannot differentiate a median nerve lesion at the pronator teres from a more proximal lesion. [84]  In addition, proximal median neuropathy is frequently normal preoperatively. [64]

Measurement of nerve conduction velocity

The velocity of motor and sensory nerve conduction is measured across definite landmarks. Latency greater than 3.5 ms or asymmetry of conduction velocity greater than 0.5 ms as compared with that of the opposite hand indicates possible entrapment neuropathy. Each segment of the upper extremity can be isolated for specific measurement.

Generally, an increase in sensory latency is observed first, and upon progression of the disease, an increase in the latency of motor fibers is seen. These studies assess only the large myelinated fibers, not the small ones that mediate pain. Nerve conduction studies may be less dependable when there is multiple levels of damage or when a systemic polyneuropathy is present.

Sensibility testing

Sensibility tests can be used to identify compressive neuropathies associated with sensory loss. These include two-point discrimination, Semmes-Weinstein monofilament (SWM) testing, and Strauch's ten test. The SWM test is more reliable, but it is time-consuming. [85]

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