Electrophysiological characteristics of polyneuropathy in POEMS syndrome: comparison with CIDP

The purpose of this study was to evaluate the electrophysiological characteristics of polyneuropathy in POEMS syndrome.

A total 46 patients with POEMS syndrome and 46 patients with chronic inflammatory demyelinating polyneuropathy (CIDP) were included in this study. Six nerve conduction parameters including (1) motor conduction velocity, distal compound muscle action potential; (2) conduction block and temporal dispersion; (3) motor distal latency; (4) F wave; and (5) sensory conduction velocity were reviewed for the subjects in both POEMS and CIDP groups.

The frequency of nerve unresponsiveness in the lower limbs of the POEMS group (motor responses were absent in 37.7% and sensory was absent in 41.7% of the patients) was higher than that of the CIDP group (motor responses were absent in 18.4% and sensory was absent in 24.4% of the patients). The peroneal motor conduction velocity was slowed, compound muscle action potential was lower, and distal latency was longer in POEMS groups than those in CIDP group. The percentage of prolonged distal compound muscle action potential duration, conduction velocities, distal latencies, and the absent F waves compatible with demyelination were significantly different between the two groups. Abnormal temporal dispersion was rarely seen, and conduction block was not observed in the patients with POEMS syndrome.

The findings suggest that peroneal nerves are more severely involved, temporal dispersion of the distal compound muscle action potential and conduction block are less common, and there are less alterations of conduction (less demyelination) as evidenced by more normal distal latencies, conduction velocities, and F-wave latencies in POEMS syndrome. These features may be useful for the differentiation between POEMS syndrome and CIDP.