Hashimoto's encephalopathy is a rare neurological disorder of unknown cause associated with thyroid autoimmunity. The disease may present in two types - a sudden vasculitic type or a progressive subacute type associated to cognitive impairment and psychiatric symptoms.

Report a case of a patient with Hashimoto's encephalopathy presenting with neuropsychiatric symptoms.

Highlight the diagnostic difficulties of medical disorder presenting with clinical features overlapping psychiatric syndromes.

Review of the scientific literature and patient's clinical notes.

A 61-year old female without previous psychiatric history was referred to psychiatry consultation for depressive symptomatology in the last year. She was prescribed with antidepressants with some initial overall improvement, but gradually developed, during the next nine months, cognitive impairment with loss of skills to be independent and increasing tremor of the extremities. Neurological evaluation was requested which revealed frontal functions impairment. Blood workup only found increased titers of anti-thyroid antibody. EEG showed mild bitemporal slowing, brain MRI was normal and brain SPECT scan revealed fronto-temporo-parietal hypoperfusion. Hashimoto encephalopathy was presumed and corticoids were started with significant improvement of neuropsycological symptoms and tremor. After one year she remains assymptomatic.

Hashimoto's encephalopathy is a diagnosis of exclusion and clinical suspicion is essential for its identification. This unusual disorder is often unrecognized for a long time because of the multiple and protracted neurocognitive manifestations and normal findings in several different examinations.

This case also highlights the importance for close collaboration between psychiatrists and neurologists.