Magnetic resonance imaging of the brain revealed prominent vermian cerebellar atrophy with some cortical atrophy (Figure 1). Cerebrospinal fluid test results were unremarkable for the following: Borrelia burgdorferi antibody, herpes simplex virus, and Mycoplasma pneumoniae by polymerase chain reaction, fluorescent Treponema antibody, paraneoplastic antibodies (including anti-Ma, Ri, Hu, Yo, Ta, CV2, Zic-4), angiotensin-converting enzyme, oligoclonal bands, 14-3-3 protein, and nonspecific enolase. Cytological examination and flow cytometry did not identify abnormal cells. Fungi, bacteria, and viral cultures did not reveal any growth. Serum studies included evaluations for anticardiolipin antibodies, gliadin antibodies, endomysial antibodies, thyroid peroxidase antibodies, vitamin E, vitamin B1, vitamin B12, homocysteine, free thyroxine, and thyroid-stimulating hormone, and these were either absent or unremarkable. Arsenic, lead, and mercury levels were unremarkable. Testing did reveal an elevated thyroglobulin antibody level of 30.7 IU/mL (reference range, 0.0-14.4 IU/mL), an elevated thyroid-stimulating hormone receptor antibody level of 17% (negative range, < 10%), and a slightly elevated cerebrospinal fluid protein level of 61 mg/dL (reference range, 15-45 mg/dL). Samples of cerebrospinal fluid and serum failed to show any immunoreactivity against rat brain tissue. Results of ultrasonography of the thyroid were also unremarkable. Electroencephalography results were normal. Nerve conduction studies and electromyography did not reveal any abnormalities.