Atypical electrophysiologic findings in chronic inflammatory demyelinating polyneuropathy (CIDP)--diagnosis confirmed by nerve biopsy.

OBJECTIVES: Numerous sets of electrophysiological criteria of chronic inflammatory demyelinating polyneuropathy (CIDP) have been proposed, among which the criteria established by an ad hoc subcommittee of the American Academy of Neurology (AAN) in 1991 (Neurology 41 (1991) 617) are the most widely used. As they seemed rather restrictive, the Inflammatory Neuropathy Cause and Treatment (INCAT) group (Ann. Neurol. 50 (2001) 195) proposed modifications of these electrophysiological criteria. However, even using these criteria, some cases of CIDP may not be recognized. In such cases, nerve biopsy has proven useful for confirmation of the diagnosis by demonstrating specific abnormalities. The objective of the study was to determine the profile of electrophysiological abnormalities in patients with atypical electrophysiologic criteria of CIDP and the diagnostic value of multiple A waves and a low median to sural amplitude ratio. PATIENTS AND METHODS: Over a period of 3 years, we classified 44 patients into two categories: those presenting the strict AAN and/or INCAT criteria and those who we regarded as cases of CIDP not meeting these criteria. All patients benefited from one or more clinical and electrophysiological examination. Extensive biological workup and genetic study when appropriate excluded other causes of neuropathy. Nerve biopsies were taken from all patients and samples were included in paraffin and epon for systematic light, teasing and electron microscopic examination. RESULTS AND CONCLUSION: Out of 44 patients, 36 fulfilled the INCAT or AAN criteria. In eight other patients, the diagnosis of CIDP was suspected on clinical and EMG examinations and confirmed by nerve biopsy. In these cases, the electrophysiological exploration showed some abnormalities such as multiple A waves in four out of eight patients or an abnormal pattern of the sensory responses of the median and sural nerves in four out of eight patients that were more indicative of an initial demyelinating process. Six of our patients received immunomodulatory treatment, and five responded favorably.