RESUMO
Hypothyroidism is commonly associated with a variety of psychiatric conditions, most commonly depression and cognitive impairment, but up to 5% to 15% of symptomatically hypothyroid patients may develop a nonaffective psychosis, classically referred to as "myxedema madness." We report the case of a woman who developed Capgras syndrome in the context of hypothyroidism, and whose psychosis rapidly resolved with levothyroxine supplementation. To date, very few cases of Capgras syndrome related to hypothyroidism have been reported. The pathophysiology of this condition remains unclear but it may be related to global cerebral hypometabolism or possibly to increased cerebral dopamine. Given the robust response of "myxedema madness" to thyroid replacement, psychiatrists should remain vigilant for covert hypothyroidism in patients with psychosis and atypical histories or presentations.