Patterns of nerve conduction abnormalities in POEMS syndrome

Polyneuropathy, organomegaly, endocrinopathy, M protein, and skin changes (POEMS) syndrome is a rare cause of demyelinating and axonal neuropathy. POEMS syndrome and chronic inflammatory demyelinating polyneuropathy (CIDP) cause peripheral nerve demyelination, and the electrodiagnostic findings may therefore be similar, but the two disorders are distinct. To elucidate the electrodiagnostic features of POEMS syndrome, we reviewed nerve conduction studies of 8 patients, and compared their results with those in 42 patients with CIDP. The patients with POEMS syndrome showed (1) slowing of nerve conduction that was more predominant in the intermediate than distal nerve segments, (2) rare conduction block (6% of the tested nerves), and (3) more severe attenuation of compound muscle action potentials in the lower than upper limbs. Findings in the CIDP patients were characterized by multifocal conduction slowing that was occasionally dominant distally, frequent conduction block (44% of tested nerves), and less discrepancy between upper and lower limb nerves. The pattern of nerve conduction abnormalities differs between these disorders. Recognition of these typical patterns may be helpful for early diagnosis of POEMS syndrome.