In terms of explaining real-world functioning, a continuum perspective of psychopathology based on burden of symptoms may perform better than the traditional Diagnostic and Statistical Manual of Mental Disorders 5th Edition (DSM-5) nosology, according to a study recently published in Schizophrenia Research. Cognitive function showed sample-dependent results.
This study included 2 independent samples: the New Mexico (NM) sample with 162 participants with a psychotic spectrum disorder, and the Bipolar and Schizophrenia Network on Intermediate Phenotypes (B-SNIP) sample with 579 participants with psychotic spectrum disorder. There were 64 healthy, matched controls in the NM sample and 717 in the B-SNIP sample. Participants had diagnoses of schizophrenia (NM, n=93; B-SNIP, n=236), schizoaffective disorder (NM, n=15; B-SNIP, n=148), or bipolar disorder Type I (NM, n=42; B-SNIP, n=195). A symptom burden-based continuum classification was compared with standard DSM nosology for identification of real-world and cognitive dysfunction. The relationship of variance and classification scheme, which included a three-cluster symptom burden-based solution, a positive/negative symptom burden, or DSM diagnosis, was investigated using linear regressions.
In both samples, real-world functioning was accounted for more by continuous and clustered classification schemes based on symptom burden than by DSM diagnoses. Among the NM sample, much of the cognitive variance was captured by classification schemes based on symptom burden, although the B-SNIP sample showed approximately equal variance accountability between symptom-based classification and the DSM. The strength of the negative symptom-cognitive deficit relationship may have mediated the results.
Limitations to this study included debate on the specificity of standard neuropsychological batteries, a relatively higher level of severity for schizophrenia and schizoaffective disorder compared with bipolar disorder I. Another limitation is that the original intent of the DSM nosology was to increase reliability of diagnosis.
The study researchers conclude that “a continuum perspective based on symptom burden accounted for greater variance in real-world functioning than traditional DSM diagnostic nosology, whereas results for cognitive dysfunction were sample dependent. Continuum based perspectives may potentially serve as a powerful mediating or moderating variable for determining outcomes during clinical trials.”
Hanlon FM, Yeo RA, Shaff NA, et al. A symptom-based continuum of psychosis explains cognitive and real-world functional deficits better than traditional diagnoses [published online January 30, 2019]. Schizophr Res. doi: 10.1016/j.schres.2019.01.024