Multiple myeloma presenting as isolated sixth cranial nerve palsy.

Multiple myeloma with isolated third nerve palsy as the presenting complaint is a rare entity. We report a case of a 30-year-old man who developed sudden onset left-sided complete abducens nerve palsy without pain. Cranial and orbital magnetic resonance imaging and cerebrospinal fluid examination demonstrated no abnormalities. He was diagnosed as having IgG type multiple myeloma, based on the immunological and pathological investigation. After instituting chemotherapy, palsy resolved within 3 weeks. Etiology is not established beyond doubt but probably palsy was caused by nerve ischemia due to hyperviscosity of the serum.