If you work in an inpatient setting or an outpatient setting with severe mental illnesses, it’s likely that a common diagnosis you see is schizoaffective illness (SI). What does this diagnosis mean? What does it imply terms of treatment? Is it a real thing? These are all questions that are important for clinical practice. In this special article, PL examines how to understand schizoaffective illness, and important clinical pitfalls.
Our understanding of SI can be organized in five different theories. One approach holds that SI is its own illness, separate from others, as appears to be the case superficially by its separate diagnostic criteria in DSM-5. A second model holds that SI represents a middle clinical picture on a psychotic continuum that extends from bipolar disorder to schizophrenia; in other words, this model rejects the Kraepelinian dichotomy of bipolar disorder and schizophrenia. A third model argues that SI represents the comorbidity of affective disorders and schizophrenia, thereby maintaining the Kraepelinian dichotomy and explaining overlap symptoms as chance co-occurrence. A fourth theory views SI as a variant of bipolar illness, and a fifth as a variant of schizophrenia.
For most clinicians, the term “schizoaffective” simply applies to individuals with continuous psychotic and mood symptoms. Unlike mood conditions, psychotic symptoms aren’t brief. And unlike schizophrenia, mood symptoms aren’t absent. Clinically, many patients seem to fall into this overlap region. In fact, the original paper describing the occurrence of such patients with such overlap was published in 1933. Indeed, Kraepelin himself observed that a good number of patients had such overlap of manic-depressive and dementia praecox symptoms. Hence, the fact that such overlap occurs is almost universally accepted, even by Kraepelin, who originated the idea that mood and psychotic conditions differ.
By itself, the presence of overlap doesn’t invalidate the diagnoses of schizophrenia and manic-depressive illness. This is partly because phenomenology is only one of four diagnostic validators (along with course, genetics, and treatment effects). This is also partly because a difference in symptoms is not an all-or-nothing phenomenon. In other words, to say that schizophrenia and manic-depressive illness differ in symptoms isn’t to say that they never overlap. It only means that they usually don’t overlap. And indeed, excellent epidemiological studies have shown that patients with mood and psychotic symptoms tend to differentiate into two big groups, one with mainly mood symptoms and one with mainly psychotic symptoms, although there is some overlap.
It is sometimes argued that the mere existence of SI is a counterexample to the Kraepelinian dichotomy of schizophrenia and manic-depressive illness. As should be clear from the above considerations, this isn’t the case. Some overlap is expected; and symptoms are only one aspect of diagnostic validation. To refute the Kraepelinian diagnostic schema, one would also need to look at genetic, course, and treatment response.
SI isn't found mainly in families of persons with SI. Rather, classic research suggests a unique pattern. In some studies of families of persons with bipolar illness, there is an increased prevalence of schizoaffective illness, bipolar type. In families of persons with schizophrenia, there is an increased prevalence of schizoaffective illness, depressed type. And comparing both major groups, SI is more prevalent in families of persons with schizophrenia or bipolar illness than in control populations or than in families of persons with SI.
These results are consistent with three possibilities. In some persons, schizoaffective illness, bipolar type appears to be a more severe variant of bipolar illness. In others, schizoaffective illness, depressed type appears to be a less severe variant of schizophrenia. In still others, seems to run in both families of manic-depressive illness. In this last group, two explanations seem possible:
SI appears to have an intermediate course between bipolar illness and schizophrenia. It’s more severe than the former, less so than the latter. These outcomes would be consistent with both subtypes of being a mild version of schizophrenia or a severe version of bipolar illness. These course data could also support the continuum view. However, there’s not a completely unique course to this illness, different than both schizophrenia or bipolar illness, and thus course data aren’t consistent with the concept that schizoaffective illness is a uniquely separate disease.
This is the least specific diagnostic validator. There are few studies of treatment of SI, but it is generally thought that these patients require long-term treatment with antipsychotic agents, as in schizophrenia, and long-term treatment with either mood stabilizers (bipolar type) or antidepressants (unipolar depressed type) as in the corresponding affective disorders. Again, this treatment response pattern is consistent with all four models except the separate illness model.
What are we to conclude? What appears most clear is that, its appearance in DSM-III-5 notwithstanding, schizoaffective illness does NOT represent a separate illness distinct from schizophrenia and manic-depressive illness. Studies of symptomatology vary, but excellent studies tend to find a difference in symptoms in psychotic and affective populations that more or less falls along the lines of Kraepelin’s dichotomy. While there are overlap areas, such overlap is empirically expected in a biological distribution of any group.
If SI represents a comorbidity of schizophrenia and manic-depressive illness, one would expect an epidemiological prevalence that is significantly lower than the other two. In other words, SI should be infrequent, since comorbidity shouldn’t be overly frequent by chance. Despite clinical impressions otherwise, epidemiological prevalence studies demonstrate that SI is diagnosable infrequently in the general community, in less than 0.5% of the population, much lower than accepted prevalence rates for schizophrenia (1%) or bipolar disease (2-4%).
Now we have a way of thinking about schizoaffective illness that allows us to identify these three basic types of patients, and then to target treatments differentially.