Fregoli syndrome in an adolescent with Moyamoya disease.

Moyamoya disease (MMD) is a progressive cerebrovascular disorder characterised by distal internal carotid artery (ICA) stenosis and compensatory collateral vessel formation. Psychiatric manifestations are rare, particularly in children. We report the case of an early adolescent with previously diagnosed MMD who developed acute-onset psychosis following a febrile illness associated with headache and vomiting. Symptoms included auditory hallucinations, persecutory delusions, emotional lability and Fregoli syndrome, a rare condition in which different strangers are believed to be a familiar person in disguise. Neuroimaging revealed bilateral ICA narrowing with extensive collateral networks. Infectious, autoimmune and metabolic evaluations were unremarkable. The patient underwent superior temporal artery-middle cerebral artery bypass with encephalo-duro-arterio-myo-synangiosis. Psychotic symptoms resolved after surgery, and he returned to baseline functioning within 1 month. This case highlights the importance of considering cerebrovascular aetiologies in abrupt-onset childhood psychosis, even in the absence of major neurological deficits.