Electrodiagnostic tests (e.g., nerve conduction studies and electromyography) are helpful adjuncts to the work up of a variety of peripheral nerve injury patterns.
However, it is vitally important to treat the patient and not the test results.
Unfortunately, as with any other test in medicine, misleading errors may occur, including false positives, false negatives, incorrect interpretation of results, and the default printout of ‘normal’ as the standard on many electrodiagnostic machines. Remember the test is only as experienced as the tester doing it. When an “outside” test does not make sense, have someone more experienced redo the test.
The ordering physician must communicate clearly what they are trying to find out, particularly with complex injury patterns where the goal might be both diagnosis of what is injured, as well as confirmation of what is uninjured and might be useable as a donor motor nerve in nerve transfers.
For example, for compression neuropathy, certain sites (such as median nerve at the wrist or ulnar nerve at the elbow) have test results that more reliably provide informative clinically relevant data:
• Suspicion of median nerve compression at the wrist can be confirmed by nerve conduction studies.
• Degree of distal thenar denervation can be evaluated by adjunctive electromyography.
• Overall, electrodiagnostic tests can be very helpful in eliminating more central or non-surgical etiologies of disease such as diabetic polyneuropathy.
For example, more complex closed brachial plexus injuries often benefit from serial electrodiagnostic testing to assess for recovery, especially electromyography:
• Don’t test too early, as it takes time for signs of denervation of the muscle to show up on electromyography. It usually takes 6 weeks for fibrillations to appear and 8 to 12 weeks for MUP’s to develop so a very early test will not be helpful.
• Consider testing at 4-6 weeks post injury to establish baseline information and look for:
• Signs of nerve root avulsion with denervation of proximal musculature such as the paraspinal muscles, rhomboids, etc. Also, with root avulsion, even though the patient will have no sensation in the affected root distribution, the sensory nerve conduction will be normal because the lesion is proximal to the dorsal root ganglion.