AbstractMonoclonal gammopathy of undetermined significance (MGUS) is the most common paraproteinemia associated with polyneuropathy. Although the clinical and electrodiagnostic manifestations most resemble those of chronic inflarnmatory demyelinating polyneuropathy, some patients manifest a pure sensory neuropathy or neuronopathy. The M protein is usually IgM, and its concentration in serum is low. Nerve pathology from patients with demyelinating disease shows a reduction of large myelinated fibers and segmental demyelination with remyelination. In some cases, the M protein possesses antibody activity against components of the myelin sheath or axon. These neuropathies may respond to treatment with steroids, immunosuppressant agents, and plasma exchange.