Objective: To elucidate the frequency of peripheral nerve demyelination in multiple sclerosis (MS). There are a number of case reports describing MS patients associated with demyelinating neuropathy, but its frequency in a whole MS population is unknown.
Methods: Extensive nerve conduction studies were prospectively performed in 60 consecutive patients with relapsing-remitting MS. Multiple excitability measurements using threshold tracking were also performed in median motor axons and superficial radial sensory axons.
Results: Nerve conduction abnormalities suggestive of demyelination were found for 3 (5%) of the patients. Two of them developed clinically evident neuropathy, whereas the remaining one had only generalized areflexia in addition to MS symptoms/signs. In all the three, MS preceded demyelinating neuropathy by several years. Excitability testing showed that supernormality and threshold electrotonus at the tested sites (median motor axons at the wrist, and radial sensory axons at the mid-forearm) were similar in the normal and MS groups.
Conclusions: MS patients do not generally have peripheral nerve demyelination, but approximately 5% of patients develop demyelinating neuropathy. The association could result from a common pathogenesis possibly due to epitope spreading during the long course of MS.
Significance: Association of chronic inflammatory demyelinating polyneuropathy with MS is not frequent, but needs to be recognized as a treatable condition.