Uniform demyelination and more severe axonal loss distinguish POEMS syndrome from CIDP

ObjectivePOEMS syndrome (the acronym reflects the common features: Polyneuropathy, Organomegaly, Endocrinopathy, Monoclonal protein and Skin changes) is a paraneoplastic disorder with a ‘demyelinating’ peripheral neuropathy that is often mistaken for chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). The nerve conduction study (NCS) and electromyography (EMG) attributes that might differentiate POEMS from CIDP and lead to earlier therapeutic intervention were explored.MethodsNCS/EMG of POEMS patients identified through retrospective review from 1960 to 2007 were compared with matched CIDP controls.Results138 POEMS patients and 69 matched CIDP controls were compared. POEMS patients demonstrated length dependent reduction in compound muscle action potentials, low conduction velocities, prolonged distal latencies and prolonged F wave latencies. Compared with CIDP controls, POEMS patients demonstrated: (1) greater reduction of motor amplitudes, (2) greater slowing of motor and sensory conduction velocities, (3) less prolonged motor distal latencies, (4) less frequent temporal dispersion and conduction block, (5) no sural sparing, (6) greater number of fibrillation potentials in a length dependent pattern and (7) higher terminal latency indices (TLI). TLI ≥0.38 in the median nerve demonstrated a sensitivity of 70% and specificity of 77% in discriminating POEMS from CIDP.ConclusionsNCS/EMG of POEMS syndrome suggests both axonal loss and demyelination. Compared with CIDP, there is greater axonal loss (reduction of motor amplitudes and increased fibrillation potentials), greater slowing of the intermediate nerve segments, less common temporal dispersion and conduction block, and absent sural sparing. These findings imply that the pathology of POEMS syndrome is diffusely distributed (uniform demyelination) along the nerve where the pathology of CIDP is probably predominantly proximal and distal. Median motor TLI may be useful in clinically distinguishing these disorders.