What is the role of electrodiagnostic studies in the evaluation of Charcot-Marie-Tooth (CMT) disease?

Updated: May 22, 2018
  • Author: Timothy C Parsons, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

Electrodiagnostic studies are critical to narrow the differential diagnosis.

Harding and Thomas found median nerve conduction velocities below 38 m/s in patients with CMT1 and above 38 m/s in patients with CMT2. [66] Thomas and colleagues found median nerve conduction velocities averaged 19.9 m/s and ranged from 5-34 m/s in patients with CMT1. Values in the lower limb nerves were more difficult to obtain because of denervation of small foot muscles, but peroneal and tibial nerve conduction velocity averaged 17 m/sec and ranged between 10-22 m/sec. Sensory nerve action potentials were usually absent or severely reduced in amplitude, but when present, showed similar reductions in velocity (mean 22.9 m/sec). [65] Dyck and Lambert had previously shown that ulnar nerve conduction velocities were even more severely affected in patients with Dejerine-Sottas syndrome, consistently measuring less than 10 m/s. [4, 87]

Lewis and Sumner compared 18 patients with CMT1 to 40 patients with chronic acquired demyelinating neuropathies, and found that slowing was uniform both along individual nerves and between different nerves in an individual patient with CMT1. There was no evidence of dispersion or conduction block in any of these patients. They concluded that this pattern serves to distinguish patients with CMT1 from patients with CIDP or AIDP, who demonstrate more multifocality. These findings were confirmed in a larger study of 129 patients with CMT1. [88, 89]

Female carriers with CMTX often demonstrate intermediate nerve conduction velocities, averaging 45 m/sec (ranging from 26-61 m/sec), which is significantly faster than CMT1A. Affected men, by comparison, have slower conduction velocities, averaging 31 m/sec, also significantly higher than those found in CMT1. The combination of intermediate conduction velocities and more rapid velocities in affected females suggests CMTX. [78] Interestingly, Dubourg and colleagues found that the difference between the median and ulnar motor nerve conduction velocities in affected female patients differed significantly when compared to the uniform velocities found in CMT1 and healthy subjects. Men with CMTX also demonstrated uniform slowing. [48]


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