Four cases of psychosis coexisting with hypothyroidism have been reported in children and adolescents, but the psychosis was attributed to thyroid replacement therapy in three cases and hypothyroidism was thought to be etiological in only one case. This article describes a possible second case of psychosis due to hypothyroidism in an adolescent who, at age 13 years, is the youngest reported case of myxedema psychosis. Treatment of the psychosis with L-T4 produced a rapid improvement in symptoms, but obsessional symptoms persisted and responded to fluoxetine. Speculatively, the patient's comorbid obsessive–compulsive disorder may have contributed to an aggravation of anxiety symptoms or operated as a predisposing factor that led to the appearance of psychotic symptoms during the hypothyroid episode. As in many presentations of "myxedema madness" in adults, a coincidental therapeutic response to thyroid treatment cannot be ruled out, so the link between hypothyroidism and psychosis cannot be considered definitive. A discussion of the diagnostic dilemmas presented by cases of hypothyroidism and psychosis is presented, and possible biochemical interrelationships are considered. In both reported adolescent cases, psychosis was the first sign of hypothyroidism and (in contrast to most adult cases) the onset of psychosis was rapid. It is premature to offer specific guidelines about when thyroid workup would be useful or cost effective, but thyroid testing may be considered if psychosis in a child or adolescent is associated with a family history of thyroid disease, goiter, or acute onset of symptoms.
