Visual Hallucinations and Cognitive Impairment as the Initial Presentation of Severe Hypothyroidism in an Elderly Patient: A Case Report.

Background: Hypothyroidism is a prevalent endocrine disorder capable of affecting multiple organ systems. While somatic symptoms are common, prominent neuropsychiatric manifestations such as visual hallucinations and cognitive deficits are exceptionally rare as an initial presentation. This atypical clinical picture frequently leads to misdiagnosis as primary psychiatric disorders or neurodegenerative conditions. Case Presentation: We report the case of a 75-year-old male who presented with a three-month history of complex visual hallucinations and progressive cognitive decline. The hallucinations were notably dependent on environmental light. Initial assessments raised concerns about the neurodegenerative process. However, laboratory investigations revealed severe autoimmune hypothyroidism with high titers of anti-thyroid antibodies. Following timely levothyroxine replacement therapy, the patient achieved complete remission of visual hallucinations and significant cognitive recovery. Conclusions: This case illustrates that severe hypothyroidism can manifest as a reversible metabolic encephalopathy mimicking dementia. It underscores the importance of screening for thyroid dysfunction in elderly patients presenting with unexplained acute neuropsychiatric symptoms to ensure appropriate management.