Infectious disease or Hashimoto's encephalopathy flares: a case report.

Hashimoto's encephalopathy is an under-recognized and rare disease that presents a diagnostic conundrum since many features are suggestive of infectious etiologies and yet treatment is immunosuppressive medications. We describe a case of a male with a history of recurrent seizures who presented with a subacute onset of confusion, persistent leukocytosis and fever while on immunosuppressant therapy, whose response to high dose steroids was incomplete and who achieved a complete remission of all symptoms when plasmapheresis was initiated. A negative cerebrospinal fluid (CSF) and serum microbiological testing in a patient with an abnormal EEG, increased CSF protein, and elevated thyroid antibodies should prompt consideration of Hashimoto's encephalopathy.