Autoimmune diseases

NCV needs to be modified it only measures the fastest fibers

by: M.C |JUlY 4, 2020

Axonal  Polyneuropathy changes in EMG (Link) EMG/NCV section Learn about the Brain

Is Electrophysiology Insensitive in the Diagnosis of CIDP?

The clinical profile of chronic inflammatory demyelinating polyneuropathy (CIDP) is variable. Nerve conduction studies are essential for the diagnosis of CIDP; however, current electrophysiologic criteria for CIDP may not be sensitive. These authors analyzed results of nerve conduction studies and nerve biopsies in 8 patients with CIDP who did not fulfill standard electrophysiologic criteria(of 44 patients with CIDP confirmed by nerve histology). Two standard electrophysiologic criteria were used: one proposedby an ad hoc committee of the AAN (Neurology 1991; 41:617) and another by the Inflammatory Neuropathy Cause and Treatment Group (Ann Neurol 2001; 50:195).

The main electrophysiologic abnormalities were those of simpleaxonopathy in 7 patients; the other patient had almost normalelectrophysiologic results. In contrast, examination of nervebiopsies in all 8 patients revealed substantial loss of myelinated fibers; in addition, frequent histologic findings were naked axons, thinly myelinated fibers, and various degrees of onion bulbs. These histology findings were identical to those of the 36 other CIDP patients. The authors conclude that many patients with unrecognized CIDP are erroneously classified by electrodiagnosis as having chronic axonal neuropathy and that nerve biopsy shouldbe considered to further investigate a chronic idiopathic neuropathy.

Comment: This study reveals a clinical weak point of major electrophysiologic criteria for CIDP. However, the converse is also true: Sometimes, a condition is electrophysiologically demyelinative but histologically normal or axonal. Besides, electrophysiologic criteria for CIDPwere originally set for research purposes, to optimize diagnostic specificity rather than sensitivity. Identification of subtle abnormalities, such as differential slowing of motor-conduction velocity and asymmetric latencies of M- and F-waves, might improve electrodiagnostic accuracy or clinical sensitivity. Some of these abnormalities were noted among cases in the current study. A-wave-like late potentials also may be important for diagnosis because they suggest the presence of slowly conducting fibers due to demyelination. Electrodiagnosis and histologic study should be complementary.

- Masayuki Baba, MD

Dr. Baba is Associate Professor, Hirosaki University of Medicine, Hirosaki, Japan.

Published in Journal Watch Neurology June 26, 2003


Vallat JM et al. Diagnostic value of nerve biopsy for atypical chronic inflammatory demyelinating polyneuropathy: Evaluation of eight cases. Muscle Nerve 2003 Apr; 27:478-85.

Remarks: If a patient has complaints of pain and burning then only the small c-fiber is involved. In this case the EMG/NCV, will be Normal. Above study shows the patient can have a diagnosis of CIDP even with a normal EMG/NCV. Thus treatment cannot be denied. Some cases may have demylinating features on NCV yet have a normal biopsy. The biopsy may have been normal due to skip lesions in nerves some parts are normal while others are affected.

Autoimmune diseases

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