Acute ataxia, Graves' disease, and stiff person syndrome.

Stiff person syndrome (SPS) has been associated with autoimmune diseases, such as Type 1 diabetes mellitus and autoimmune thyroid disease (Hashimoto's thyroiditis), among others. The association of SPS with hyperthyroidism is extremely rare. We describe a patient with uncontrolled Graves' disease and undiagnosed SPS, who presented initially with acute ataxia simulating a cerebrovascular accident. Initiation of immunosuppressive therapy dramatically improved the patient's Graves' disease within 2 weeks but the neurological symptoms were not alleviated after a follow-up period of 3 years.