Does change in definition of psychotic symptoms in diagnosis of schizophrenia in DSM-5 affect caseness?

Psychotic symptoms are a central element in the diagnosis of schizophrenia, although their precise definition has varied through the multiple iterations of DSM and the ICD. Schneiderian first-rank symptoms (FRS) have received a particularly prominent position in the diagnostic criteria of schizophrenia since ICD-9 and DSM-III. In the current iteration of DSM (DSM-IV-TR), whereas two characteristic symptoms are ordinarily required to meet criterion A, only a single symptom is necessary if the psychotic symptom happens to be a FRS, notably a bizarre delusion or auditory hallucination of a running commentary or 'conversing voices'. Because of limited data in support of the special treatment of FRS, DSM-5 has made changes to criterion A, requiring that at least two psychotic symptoms be present in all cases with at least one of these symptoms being a delusion, hallucination, or disorganized speech. To assess the impact of these changes on the prevalence of schizophrenia, we examined a research dataset of 221 individuals with DSM-IV schizophrenia to study the prevalence and co-occurrence of various criterion A symptoms. Although bizarre delusions and/or Schneiderian hallucinations were present in 124 patients (56.1%), they were singly determinative of diagnosis in only one patient (0.46%). Additionally, only three of the 221 patients (1.4%) with DSM-IV schizophrenia did not have a delusion, hallucination, or disorganized speech. DSM-5 changes in criteria A should have a negligible effect on the prevalence of schizophrenia, with over 98% of individuals with DSM-IV schizophrenia continuing to receive a DSM-5 diagnosis of schizophrenia in this dataset.