ReviewCharacteristics and heterogeneity of schizoaffective disorder compared with unipolar depression and schizophrenia – a systematic literature review and meta-analysis
Introduction
Schizoaffective disorder is one of the most controversial diagnoses in psychiatry. Its nosological status has been debated at length (for example, Crow 1995, Evans et al. 1999, Lake and Hurwitz 2007, Jager et al., 2011), as has its justification as disease entity in general (Maier, 2006, Malhi et al., 2008, Heckers, 2009). Nevertheless, the diagnosis is frequently applied in population based and clinical samples: For instance, a Finnish epidemiological study (Perala et al. 2007) estimated a prevalence of 0.32 percent – roughly 37% of the lifetime prevalence of schizophrenia in that study. Olfson et al. (2009) reported that among Medicaid patients doctors diagnosed schizoaffective disorder almost half as frequently as schizophrenia.
Since schizoaffective disorder shares characteristics of affective disorders and schizophrenia, the differentiation from both groups of disorders is a key issue in clinical practice and in research. In an earlier meta-analysis we compared samples of patients with schizoaffective disorder with samples of patients with bipolar disorder and schizophrenia and found that most demographic, clinical, and psychometric measures fell between these two poles of the Kraepelinian dichotomy. However, samples of patients diagnosed with schizoaffective disorder were slightly more similar to schizophrenia than to bipolar disorder (Pagel et al. 2013a).
The diagnostic reliability of schizoaffective disorder is low (Jager et al., 2011, Santelmann et al., 2015 ). One of several possible reasons for low diagnostic reliability is substantial variability of a disorder. Variability, or heterogeneity, means that key characteristics of a disorder can assume a wide variety of values. For example, age at onset may span a wide range or psychopathology may be highly variable. Applied to schizoaffective disorder this model means that its highly variable (heterogeneous) psychopathology (comprising symptoms of two different groups of diagnoses: schizophrenia and affective disorders) may erroneously be ascribed to other disorders. According to this model, the diagnostic reliability of schizoaffective disorder would be lower than that of other diagnoses. This has indeed been shown (Jager et al., 2011). Given the low diagnostic reliability, we hypothesized that schizoaffective disorder would be characterized by high heterogeneity, that is, the variability of key demographic, clinical, and psychopathological parameters would be particularly large in comparison to unipolar disorder and schizophrenia. In another, earlier meta-analysis (Pagel et al., 2013b), however, we found that this is not the case for the comparison of schizoaffective disorder with bipolar disorder and schizophrenia: heterogeneity as measured across a wide range of parameters was similar for all three diagnoses. In fact, heterogeneity was slightly smaller among samples of patients with schizoaffective disorder.
In addition to bipolar disorder and schizophrenia, unipolar affective disorder is the third main differential diagnosis of schizoaffective disorder. To our knowledge, however, unipolar disorder has not been compared with schizoaffective disorder in regard to key illness characteristics and illness heterogeneity in a systematic and quantitative way. To address this knowledge gap we carried out a systematic literature review and meta-analysis comparing (1) key illness characteristics and 2) heterogeneity of key illness characteristics among schizoaffective disorder, unipolar affective disorder and schizophrenia.
Section snippets
Methods
This is a systematic review and meta-analysis of key illness characteristics and heterogeneity of key illness characteristics of schizoaffective disorder, compared with unipolar disorder and schizophrenia. This study is part of a larger research project on illness characteristics and on heterogeneity of schizoaffective disorder (Pagel et al., 2013a, Pagel et al., 2013b, Pagel et al., 2014). Design and statistical details of the project have been described in depth elsewhere (Pagel et al., 2013a
Results
We included 24 studies (Amador et al., 1994, Banov et al., 1994, Coryell and Zimmerman, 1986, Fennig et al., 1996, Grossmann et al., 1991, Levinson, 1991, Lewine et al., 1995, Maier et al., 1993, Maj, 1986, Maj et al., 1991, Mokrani et al., 2000, Opjordsmoen, 1989, Pini et al., 2001, Radomsky et al., 1999, Ragin and Oltmanns, 1987, Reichenberg et al., 2009: Sauer et al., 1984; Schott et al., 2006; Sharma et al., 1994; Silverstein et al., 1990; Tsuang & Coryell, 1993; Walterfang et al., 2009;
Discussion
This study yielded two main results: Firstly, the majority of key characteristics of patients with schizoaffective disorder fell between those for patients with schizophrenia and unipolar depression, and they were slightly more similar to samples of schizophrenia. Relative to samples of patients with unipolar disorder, schizoaffective disorder patients were on average younger at onset, had a higher percentage of men and a lower percentage of married patients. Also, psychopathology scales
Limitations
This study is limited by the relatively small number of studies that simultaneously investigated samples of patients with unipolar, schizoaffective, and schizophrenic patients (N=24). In earlier comparisons of schizoaffective disorder and schizophrenia with bipolar disorder (Pagel et al., 2013a, Pagel et al., 2013b) we were able to include twice as many papers (key characteristics: 50 studies, heterogeneity: 47 studies). The low number of studies may explain why some figures for schizophrenia
Conclusions
Our results indicate that schizoaffective disorder indeed falls between schizophrenia and affective disorders, thereby adding to the validity of the diagnosis – at least as long as an intermediary position between schizophrenia and affective disorders is central to the definition of schizoaffective disorder. On the other hand, whether schizoaffective disorder is a useful clinical diagnosis depends on other factors as well, such as reliability and the presence of specific treatments. Finally,
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Both authors share first authorship because they contributed equally to this work