Autoimmune thyroiditis and a rapidly progressive dementia: global hypoperfusion on SPECT scanning suggests a possible mechanism.

We report the clinical, laboratory, EEG, and SPECT findings in a 59-year-old euthyroid woman with previously undiagnosed autoimmune thyroiditis, subclinical hypothyroidism, and rapidly progressive dementia. We made a diagnosis of Hashimoto's encephalopathy based on elevated thyrotropin, abnormal EEG, and clinical improvement after thyroid hormone replacement. SPECT demonstrated global hypoperfusion with normalization on clinical recovery, suggesting a possible mechanism for the pathogenesis of Hashimoto's encephalopathy.