Monoclonal gamrnopathy of undetermined significance (MGUS) is the most common paraproteinemia associated with polyneuropathy. Although the clinical and electrodiagnostic manifestations most resemble those of chronic inflammatory 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.
MUSCLE & NERVE 12~1-8 1989
Determining the etiology of a peripheral neuropathy is often a frustrating experience for the patient and physician. Dyck et al.lx identified a specific cause in only 76% of cases, even when special diagnostic tests were utilized. In some of the patients, up to 10% in one study,'2 a monoclonal gammopathy can be identified. The paraprotein can be due to any of the plasma cell dyscrasias. Electi-odiagnostic testing can be helpful in classifying these patients." The subsequent case report describes a patient with peripheral neuropathy and monoclonal gammopathy of undetermined significance (MGUS) and illustrates the diagnostic approach to categorizing these patients.
CLINICAL HISTORY
A 60-year-old man was referred for a %year history of progressive extremity numbness and paresthesias without pain and a 1-year history of hand and thigh weakness. He denied a personal or family history of neuromuscular disease. Symptom onset was unrelated to viral infection, sur-From the