A case of rapid conversion to psychosis of delusional misidentification associated with derealisation, verbal memory impairment and FDG-PET imaging abnormalities.

The delusional misidentification syndromes, occurring within the context of different nosological settings, such as schizophrenia, are psychopathological phenomena related to the experience of depersonalisation/derealisation. Extensive research indicates that individuals meeting specific "prodromal" criteria, such as attenuated psychotic symptoms, brief intermittent psychotic symptoms, or functional decline and family history of schizophrenia have increased risk for impending psychosis. Despite depersonalisation and/or derealisation often precede psychotic onset, they are not included among the prodromal criteria of the Australian-American approach. A 17-year-old boy with acute agitation, violent behaviour and aggression, and dissociative amnesia had a mild verbal memory impairment and temporo-limbic hypometabolism on the positron-emission tomography. The patient was assessed with both the ultra-high risk (UHR) and the basic symptom approaches and was not found to be prodromal with imminent risk of transition to psychosis. He was hospitalised briefly and 2 weeks after discharge he developed delusional misidentification. This case shows that even the integration of both UHR and basic symptoms criteria may give false negatives in the prediction of psychosis, especially in those cases in which a long prodromal phase is absent.