Antineuronal (anti-Ri) antibodies in a patient with steroid-responsive opsoclonus-myoclonus.

A 45-year-old woman developed opsoclonus, myoclonus, and severe truncal and gait ataxia. Serum and CSF contained IgG antibodies that appear to be identical to "anti-Ri" antibodies associated with paraneoplastic opsoclonus and ataxia. The patient had a fluctuating course with exacerbations that responded well to corticosteroids and later to cyclophosphamide. Her anti-Ri antibody titer has declined significantly but still remains high. After more than 3 years of follow-up, no neoplasm has been detected.