The presence of a single first-rank auditory hallucination (FRAH) or bizarre delusion (BD) is sufficient to satisfy the symptom criterion for a DSM-IV-TR diagnosis of schizophrenia. We queried two independent databases to investigate how prevalent FRAH and BD are in schizophrenia spectrum disorders and whether the diagnosis depends on them. FRAH was common in both datasets (42.2% and 55.2%) and BD was present in the majority of patients (62.5% and 69.7%). However, FRAH and BD rarely determined the diagnosis. In the first database, we found only seven cases among 325 patients (2.1%) and in the second database we found only one case among 201 patients (0.5%) who were diagnosed based on FRAH or BD alone. Among patients with FRAH, 96% had delusions, 14-42% had negative symptoms, 15-21% had disorganized or catatonic behavior, and 20-23% had disorganized speech. Among patients with BD, 88-99% had hallucinations, 17-49% had negative symptoms, 20-27% had disorganized or catatonic behavior, and 21-25% had disorganized speech. We conclude that FRAH and BD are common features of schizophrenia spectrum disorders, typically occur in the context of other psychotic symptoms, and very rarely constitute the sole symptom criterion for a DSM-IV-TR diagnosis of schizophrenia.
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