A Case of Hashimoto's Encephalopathy Presenting with Cognitive Impairment and Visual Hallucinations

ABSTRACT

Introduction: Hashimoto's encephalopathy (HE) is a rare immune–mediated complication of Hashimoto thyroiditis. It is presented as subacute onset of altered mental status with confusion, seizures and myoclonus. It is a diagnosis of exclusion and requires that all other possible causes of cognitive impairment are excluded with a response to steroid therapy and evidence of thyroid autoimmunity in a patient. Here, we present a case of HE in a patient who presented with altered mental status and visual hallucinations despite no history or symptoms of thyroid disorder. Case Description A 77 year old male with past medical history of hypertension presented with altered mental status, lethargy, and visual hallucinations. Per patient’s wife, patient started to get somnolent and was having memory problems six weeks prior to presentation. His mental status gradually deteriorated, and he started to have visual hallucinations. He was somnolent and noted to have myoclonus and twitching on admission. Magnetic resonance imaging (MRI) of the brain with gadolinium showed chronic microvascular changes with no acute intracranial pathology or masses. Electroencephalogram (EEG) showed no signs of epileptiform activity. Infectious disease work up, including complete blood count, urinalysis, sexually transmitted diseases, and cerebrospinal fluid (CSF) analysis, was negative. Blood glucose levels, serum electrolytes, liver function tests, blood urea nitrogen, and creatinine were normal. Coronavirus disease 2019 (COVID-19) was negative. CSF analysis for autoimmune encephalopathy and Creutzfeldt-Jakob disease was negative. Thyroid function tests were normal. Thyroid peroxidase antibody (TPOAb) was negative (8.6 IU/mL [reference range (RR) < 9.0 IU/mL]) and TgAb was positive (8.2 ng/ mL [RR < 4 IU/ mL]). With suspicion of Hashimoto's encephalopathy, he was started on intravenous Solu-Medrol 1 g for five days. He was then switched to oral prednisone 60 mg daily, which he received for ten days. His mental status improved upon day 14 of admission. On day 17 of admission, he was discharged on oral prednisone 40 mg daily with taper for five weeks. He was evaluated in the clinic few months after discharge. His mental status had improved significantly, and he was back to his baseline in about two months after discharge as per his wife. Repeat thyroid function tests, TPOAb, and TgAb were negative. Discussion: The incidence of Hashimoto’s encephalopathy (HE) is 2.1 per 100,000 individuals in the general population, and is more common in women than men. This case highlights that HE should be considered in patients with subacute presentation of neurological problems, which cannot be explained with other possible diagnosis, despite no symptoms of thyroid disease such as the patient in this case study. Therefore, HE should be evaluated for in patients with cognitive impairment for prompt diagnosis and treatment with steroid therapy in order to improve the prognosis in these patients.