[A 66-year-old woman with confusion, aphasia, and myoclonus]

Hashimoto's encephalopathy, also called steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT), is a rare syndrome with an unknown pathogenesis. Clinical onset is insidious or acute with variable neurological symptoms. Spinal protein is elevated in most cases, but findings are non-specific in routine blood tests and on cerebral CT and EEG. The most important diagnostic clue is elevated levels of thyroid antibodies, especially anti-thyroid peroxidase antibody (anti-TPO). Administration of corticosteroids is the treatment of choice and usually results in complete recovery.

A 66-year-old woman had experienced episodic neurological symptoms over a few weeks. On admission she demonstrated moderate aphasia, tremor and myoclonus, but no other focal neurological signs. A cerebral CT scan and routine blood tests did not provide diagnostic clues. The cerebrospinal fluid protein level was markedly elevated, and treatment with antibiotic and antiviral agents against possible encephalitis was started. However, the clinical condition did not improve. Further testing showed elevated levels of anti thyroxine peroxidase (aTPO) antibodies. Based on this finding, and after exclusion of other causes, the patient was diagnosed with Hashimoto's encephalitis. On treatment with systemic steroids, the clinical condition improved over a few days.

Hashimoto's encephalitis is a rare syndrome. Still, it is important to diagnose patients correctly. Treatment with steroids induces marked clinical improvement and usually confers a good prognosis.