Abstract
We describe a 64-year-old male who presented with a 2-year history of behavioral and cognitive decline. Brain imaging showed nonenhancing hemispheric white matter lesions. Blood work revealed elevated thyroglobulin and thyroperoxidase antibody levels. Cerebrospinal fluid (CSF) analysis was largely negative, except for an elevated protein and immunoglobulin G (IgG) level. Because of the absence of stroke, central nervous system (CNS) tumor, or infection, this patient fits into criteria of Hashimoto's encephalopathy. His Mini-Mental State Examination score improved from 10 to 29 after initial immunotherapy. The patient remained stable over 6 months with monthly outpatient total plasma exchange, but symptoms recurred within 3 months when the outpatient therapy was discontinued. A follow-up CSF IgG level was found to be increased and the treatment was repeated with partial clinical improvement and decline in CSF IgG level. He then underwent high dose steroid treatment after which patients' clinical condition stabilized and CSF analysis showed even further IgG decline.