Background Electrophysiological demyelination of sensory nerves is not routinely assessed in the evaluation of suspected chronic inflammatory demyelinating polyneuropathy (CIDP). Its usefulness is unknown.
Methods We compared in 19 patients with typical chronic inflammatory demyelinating polyneuropathy (CIDP) and 26 controls with distal large fibre sensory axonal neuropathy, forearm median sensory conductions, sensory nerve action potential (SNAP) amplitudes and durations, and sensory nerve conduction velocities (SNCVs) of median, radial and sural nerves.
Results Median nerve sensory conduction block (SCB) across the forearm was greater in CIDP patients than controls (p=0.005). SNAP durations were longer in CIDP patients for median (p=0.001) and sural nerves (p=0.004). SNCVs were significantly slower for median and sural nerves in CIDP patients. Median SCB or prolonged median SNAP duration or prolonged sural SNAP duration, offered a sensitivity of 73.7% for CIDP and specificity of 96.2%. As additional parameters, they improved diagnostic sensitivity of the American Academy of Neurology (AAN) criteria for CIDP of 1991, from 42.1% to 78.9% in this population, with preserved specificity of 100%.
Discussion Sensory electrophysiological demyelination is present and may be diagnostically useful in typical CIDP. SCB detection and SNAP duration prolongation appear to represent more useful markers of demyelination than SNCV reduction.
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