Analysis Supports DSM-5 Changes to Schizophrenia Criteria

The changes in the criteria for schizophrenia that appear in DSM-5—including the addition of a scale for severity of dimensions of psychosis—appear to be valid and useful, according to an analysis of a large dataset of double-blind, randomized placebo-controlled schizophrenia trials.

The analysis, appearing in the May Schizophrenia Bulletin, examined the effect of three major changes to the DSM criteria: the requirement for the presence of at least two criterion A symptoms, one of which must be delusions, hallucinations, or disorganized thinking (the core “positive symptoms” that are necessary for a reliable diagnosis of schizophrenia); removal of the schizophrenia “sub-types” that had been included in previous editions; and the addition (in Section 3 of the manual, but not in the main text) of a scale for assessing the severity of symptom dimensions.

The report, by Taina Mattila, M.D., and colleagues from the Medicines Evaluation Board in the Netherlands and the Department of Psychiatry at the University of Amsterdam, supports those changes. “Our analysis of about 5,000 patients diagnosed according to pre-DSM-5 criteria for schizophrenia provide empirical support for the validity of the changes in the section concerning schizophrenia in DSM-5,” they stated.

Mattila and colleagues examined data from 22 short-term efficacy registration trials of second-generation antipsychotics (SGAs) for the treatment of acute psychotic episodes in patients with schizophrenia (n=5,233) submitted to the Dutch C-registry. They looked at whether patients in the pre-DSM-5 trials would also meet criteria the criteria for DSM-5 schizophrenia, tested whether DSM-IV schizophrenia subtypes predicted treatment response to SGAs, and examined the validity of the Clinician-Rated Dimensions of Psychosis Symptom Severity (C-RDPSS) scale in section 3 of DSM-5.

All patients in the registration trials except one had at least two criterion A symptoms, and only 22 patients (0.4 percent of the total cohort) did not have any of the required three positive symptoms. “Altogether, the vast majority of patients (more than 99.5 percent) of patients with schizophrenia in these pre-DSM-5 trials would have met DSM-5 criteria for schizophrenia,” the researchers stated.

The finding corroborates a much smaller study by Rajiv Tandon, M.D., and colleagues showing that less than 2 percent of patients with DSM-IV schizophrenia would not meet DSM-5 criteria for schizophrenia. That study, “Does Change In Definition of Psychotic Symptoms in Diagnosis of Schizophrenia in DSM-5 Affect Caseness?,” appeared in the June Asian Journal of Psychiatry. “Together these findings suggest that results of clinical trials in patients with pre-DSM-5 schizophrenia are valid for patients diagnosed with DSM-5 schizophrenia,” Mattila and colleagues wrote.

Vito Sesuknas

In an interview with Psychiatric News prior to publication of DSM-5, William Carpenter, M.D., chair of the DSM-5 Psychotic Disorders Work Group and editor of Schizophrenia Bulletin, predicted the major changes to the chapter on psychotic disorders would be unlikely to affect case prevalence, but they reflect conceptual changes that would make the criteria more accurately reflect individual patient presentation.

Regarding the change to criterion A requiring a patient to have a minimum of two symptoms rather than a single bizarre delusion, Carpenter said, “It’s an important conceptual change because it’s a mistake to give that primacy to a single bizarre delusion, but we don’t think it will make a difference in caseness because it almost never happens in nature.”

Mattila and colleagues also looked at differences in response to antipsychotic treatment according to the five “subtypes” used in DSM-IV—disorganized, catatonic, paranoid, residual, and undifferentiated. Those subtypes were removed from DSM-5 because there was no evidence that they were clinically useful.

They found that there was no significant difference in treatment response based on the scores at six weeks on the Brief Psychiatric Rating Scale (BPRS) in the drug registration trials. “The effect of SGAs do not differ between DSM-IV schizophrenia subtypes, thus providing empirical support for the decision to remove the subtypes in DSM-5,” they wrote.

Finally, Mattila and colleagues showed that the C-RDPSS scale is clinically useful when applied to the patients in the pre-DSM-5 registration trials. (To obtain a proxy for the C-RDPSS scores, four independent psychiatrists blindly assigned the best corresponding BPRS items to the C-RDPSS dimension and applied statistical analysis to derive an adjusted standardized score for the effect of medication on a particular dimension.)

They found that the symptom dimensions that respond best to treatment with SGAs are hallucinations, delusions, disorganized speech, and mania. Showing less improvement were abnormal psychomotor behavior, negative symptoms, depression, and cognitive impairment.

“The DSM-5 C-RDPSS scale adds valuable information to the categorical diagnosis of schizophrenia, which is relevant for antipsychotic response,” the researchers stated. ■