Hashimoto's encephalopathy (HE) is a rare neuropsychiatric syndrome associated with antithyroid
antibodies. It may have an acute onset (episodes of
cerebral ischemia, seizure, and
psychosis) or it may present as an indolent form (depression,
cognitive decline,
myoclonus,
tremors, and fluctuations in level of consciousness). We here describe a case of
encephalopathy presenting as
non-convulsive status epilepticus associated with Hashimoto's
thyroiditis (HT), unresponsive to
corticosteroid therapy, with improvement after
plasma exchange treatment. A previously healthy 19-year-old woman, presented
generalized tonic-clonic seizures. About a month later, she manifested a speech disorder characterized by difficulties in the production and comprehension of language. Within a few days she also developed
confusion and difficulties in recognizing familiar places, with gradual worsening over time. EEG revealed a
non-convulsive status epilepticus (NCSE). CSF examination showed slightly elevated cell count and four
oligoclonal bands. MRI was unremarkable, and (18)F-FDG brain PET showed widespread hypometabolism, mostly in posterior regions bilaterally. Laboratory and ultrasound findings showed signs of HT. Treatment with
steroid was introduced without any improvement. After five sessions of
plasma exchange there was a decrease of antithyroid
antibodies, as well as EEG and clinical improvement. Three months after discharge (18)F-FDG brain PET showed a complete normalization of the picture, and the patient was asymptomatic. This report emphasizes the successful treatment of HE with
plasma exchange in a patient who presented with NCSE. Based on the actual evidence, the term "
Encephalopathy associated with Hashimoto's
thyroiditis" may be the most proper. Furthermore, to our knowledge, this is the first case of an adult patient studied twice with an (18)F-FDG brain PET: prior to treatment with
plasma exchange, and at 3 months follow-up when the patient was clinically completely asymptomatic. Studies in more patients are needed to clarify the relevance of (18)F-FDG brain PET as a possible diagnostic tool for HE.