Characteristics and heterogeneity of schizoaffective disorder compared with unipolar depression and schizophrenia - a systematic literature review and meta-analysis.

BACKGROUND: Comparisons of illness characteristics between patients with schizoaffective disorder (SAD) patients and unipolar depression (UD) are rare, even though UD is one of the most important differential diagnoses of SAD. Also, the variability of illness characteristics (heterogeneity) has not been compared. We compared illness characteristics and their heterogeneity among SAD, UD, and - as another important differential diagnosis - schizophrenia (S).
METHODS: In order to reduce sampling bias we systematically searched for studies simultaneously comparing samples of patients with SAD, UD, and S. Using random effects and Mantel-Haenszel models we estimated and compared demographic, illness course and psychopathology parameters, using pooled standard deviations as a measurement of heterogeneity.
RESULTS: Out of 155 articles found by an earlier meta-analysis, 765 screened in Medline, 2738 screened in EMBASE, and 855 screened in PsycINFO we selected 24 studies, covering 3714 patients diagnosed according to RDC, DSM-III, DSM-IIIR, DSM-IV, or ICD-10. In almost all key characteristics, samples with schizoaffective disorders fell between unipolar depression and schizophrenia, with a tendency towards schizophrenia. On average, UD patients were significantly older at illness onset (33.0 years, SAD: 25.2, S: 23.4), more often women (59% vs. 57% vs. 39%) and more often married (53% vs. 39% vs. 27%). Their psychopathology was also less severe, as measured by BPRS, GAS, and HAMD. In demographic and clinical variables heterogeneity was roughly 5% larger in UD than in SAD, and samples of patients with schizophrenia had the lowest pooled heterogeneity. A similar picture emerged in a sensitivity analysis with coefficient of variation as the measurement of heterogeneity. LIMITATIONS: Relative to bipolar disorder there are fewer studies including unipolar patients. No studies based on DSM-5 could be included.
CONCLUSIONS: Regarding unipolar affective disorder this study confirms what we have shown for bipolar disorders in earlier studies: schizoaffective disorder falls between schizophrenia and affective disorders, and there are relevant quantitative differences in key illness characteristics, which supports the validity of the schizoaffective disorder concept. Contrary to our expectations heterogeneity is not larger in SAD than in UD and not substantially higher than in S. Lower reliability of the diagnosis of SAD therefore cannot be ascribed to higher variability of illness characteristics in SAD.