The classification of schizoaffective disorder has always been controversial. Kraepelin noted in 1919 that patients with both affective and schizophrenic symptoms complicated the differential diagnosis due to the 'mingling of morbid symptoms of both psychoses'. Kasanin first employed the term 'acute schizophrenic psychoses' in 1933 to describe a group of patients who experienced a rapid onset of emotional turmoil and psychotic symptoms, but who recovered after several weeks or months. (5) In other words, the symptoms appeared similar to schizophrenia during periods of exacerbation, but unlike schizophrenia, showed a greater tendency to remit between episodes. These features sparked an ongoing debate by the 1960s about the proper classification of schizoaffective disorder. Much of this discussion involved the possibility that schizoaffective disorder was conceptualized most accurately as follows:

1. a type of schizophrenia (e.g. 'remitting schizophrenia');

2. a type of affective disorder;

3. a unique disorder that was separate from both schizophrenia and bipolar disorder;

4. an arbitrary categorization of clinical symptoms that masks a continuum of pathology between schizophrenia and affective illness;

5. a heterogeneous collection of 'interforms' between schizophrenia and affective disorder (i.e. symptoms of both disorders).

The last possibility is not mutually exclusive of the first four; for example, one or more variants of schizoaffective disorder may be related closely to schizophrenia, while another may be related more closely to an affective disorder.

Family and outcome studies provide useful ways of assessing the relative merits of each of the possibilities outlined above. These approaches are informative although interpretations of such studies are complicated at times by the use of different diagnostic criteria across studies.

Family studies

Family studies provide an important tool for assessing the relationship between disorders. In particular, it is a type of genetic study that assumes that related disorders will coaggregate more frequently among biologically related individuals than they would in the general population. Thus, a disorder is concluded to be in the schizophrenia spectrum if it occurs more frequently among the relatives of schizophrenic patients, compared with suitable controls. Similarly, a disorder is considered to be in the affective spectrum if it occurs more frequently among the relatives of patients with affective disorders. Evidence for the inclusion of schizoaffective disorder in the schizophrenia spectrum is discussed in greater detail elsewhere (see Ch§pt§L4.3.5.1). Only representative findings pertinent to the present discussion about the classification of schizoaffective disorder will be summarized here.

Bertelsen and Gottesman(7) summarized a series of seven family studies published between 1979 and 1993, using structured diagnostic criteria. Analyses of risk to the development schizophrenia, schizoaffective disorder, and affective disorder in the first-degree relatives of patients with schizoaffective disorder, were included. In all seven studies, the relatives showed a higher risk of developing an affective disorder than of developing schizoaffective disorder. In five of the seven studies the risks of developing schizophrenia was equal to or greater than the risk of developing schizoaffective disorder. Thus, the relatives of schizoaffective patients showed generally higher risks of developing disorders other than the one with which they were diagnosed. These findings were consistent with a heterogeneous view of schizoaffective disorder, in which individual cases represented subtypes of either schizophrenia or of affective disorder. The findings were also consistent with the possibility that schizoaffective disorder represents a chance collection of 'interforms' between schizophrenia and affective disorder.

These findings were not consistent with the view that schizoaffective disorder represented a continuum between the other two disorders, because in that case, the rate of schizoaffective disorder in first-degree relatives would have been higher, compared with the rates at which these relatives developed schizophrenia or affective disorder. The findings were also inconsistent with the possibility that schizoaffective disorder represented a unique disorder that was independent of either schizophrenia or an affective disorder. In that case, the first-degree relatives of patients with schizoaffective disorder should show relatively high rates of schizoaffective disorder itself, but relatively low rates of the other disorders. Tsuang (8) and others reported similar findings using other definitions of the disorder. (5)

In the series of studies reviewed by Bertelsen and Gottesman,(7) the morbid risk for schizoaffective disorder itself ranged from 1.8 to 6.1 per cent in first-degree relatives of patients with schizoaffective disorder, which was still higher than the rate observed in the general population (see the section on epidemiology below). These results, taken together with the higher risks for both schizophrenia and affective disorder, suggest that schizoaffective disorder is a heterogeneous condition.

The results of family studies allow for a few tentative generalizations concerning the classification of schizoaffective disorder. First, they indicate the likelihood that many cases of the disorder are related to either schizophrenia or affective illness. Results from family studies are less clear about how specific subtypes should be defined.(5) Second, the family studies leave open the possibility that schizoaffective disorder is due to the additive effects of genes for both schizophrenia and affective illness. Third, the rates of schizoaffective disorder are higher among the relatives of schizoaffective patients than would be expected in the general population.

Outcome studies

A majority of outcome studies show that schizoaffective disorder has a better course than schizophrenia, but a poorer course than affective disorder. (910) For example, Samson et al.(10) reviewed 10 outcome studies reported between 1963 and 1987 that assessed patients with either schizoaffective disorder or schizophrenia. Global, marital, social, occupational, hospital course, and symptom dimensions of outcome were assessed. In each category, patients with schizophrenia showed poorer outcomes. In contrast, their review of 11 outcome studies comparing schizoaffective disorder with affective disorder showed that affective disorder was associated with equal or better outcomes on almost all dimensions. Thus, despite differences in methodology and diagnostic criteria, schizoaffective disorder was frequently associated with clinical outcomes that were intermediate between those associated with schizophrenia and those related to affective disorder.

Further evidence for this pattern was provided more recently in an epidemiological family study. (H) Schizoaffective disorder showed levels of impairment that were intermediate between schizophrenia and affective disorder on the Level of Functioning Scale (which includes nine items, such as duration of non-hospital admission, quality of social relations, symptoms, and an overall rating), and on the Scale for the Assessment of Negative Symptoms. These findings, together with family data showing increased rates of both schizophrenia and affective disorder among relatives of schizoaffective patients, were interpreted as additional evidence in favour of the (DSM-IIIR) classification of schizoaffective disorder. They were also interpreted as supportive of the hypothesis that schizoaffective disorder represents an interform of both schizophrenia and affective illness.

Marneros et al.(12> reported on outcomes in the three (modified DSM-IIIR) disorders, as part of the Cologne Longitudinal Study. The outcomes were measured by symptoms in five dimensions (psychotic symptoms, reduction of energetic potential, qualitative and quantitative disturbances of affect, and other disturbances of behaviour) that persisted for at least 3 years. Consistent with the general pattern described thus far, poor outcomes in the schizoaffective group occurred at a rate (49.5 per cent of the sample) that was intermediate between those observed in the schizophrenic (93.2 per cent) and affective groups (35.8 per cent), and differed significantly from both of them.

While these studies show schizoaffective disorder to have intermediate outcomes generally, there are some categories in which it resembles schizophrenia or affective disorder more closely. For example, Samson et al.(19) noted above that outcomes for schizoaffective disorder were equivalent to those for affective disorder in several dimensions. Marneros et al. (13> studied schizophrenic, schizoaffective, and affective subjects who were diagnosed according to narrow, modified DSM-III criteria. On some measures (e.g. psychosocial functioning, as measured by the Global Assessment Scale) the schizoaffective group performed intermediate between the affective group (which was higher) and the schizophrenic group (which was lower). On a measure of social adjustment, however, 70 per cent of the schizoaffective group was rated as good or excellent, which did not differ significantly from the 84 per cent of the affective group who received the same rating. Both groups differed significantly from the schizophrenic group, only 44 per cent of which showed a good or excellent outcome. Moreover, the schizoaffective and affective disorder groups did not differ on a rating scale of psychological impairments (e.g. body language, affect display, conversation skills, and co-operation), although both were rated as significantly less impaired than the schizophrenic group.

Both Kendler et al.(11) and Atre-Vaidya and Taylor(14) reported similarities between some types of psychotic symptoms between schizoaffective disorder and schizophrenia. The former study showed that the two groups did not differ from each other with respect to severity of delusions or positive thought disorder; the latter study showed that the two groups both demonstrated more hallucinations than did an affective disorders group, but did not differ from each other.

These overall differences in outcome further serve to validate the classification of schizoaffective disorder as a separate syndrome. Its heterogeneity, however, raises the issue of whether such intermediate outcomes might reflect the mean of a combination of mainly good and mainly poor outcomes. This in turn leads to the question of whether schizoaffective disorder can be subtyped in a useful and valid manner. If so, are better and worse outcomes associated with different variants of the syndrome?

Vaillant suggested in the 1960s that prognostic indicators, including a good premorbid level of adjustment, the presence of precipitating factors, an acute onset, confusion, the presence of affective symptoms, and a familial history of affective disorder (or the absence of a schizophrenic history), could predict remission in approximately 80 per cent of cases of 'remitting schizophrenia'.(1. I6) The inclusion of affective symptoms and a positive family history for affective illness on the list contributed (later) to hypotheses that variants of schizoaffective disorder were related to affective illness and to better outcomes. In contrast, variants associated more with schizophrenic symptoms or family history were likely to be associated with schizophrenia, and with relatively poor outcomes.

There have been a variety of attempts to subtype schizoaffective disorders, based on whether affective or schizophrenic symptoms predominate. (7,16,) Tsuang and Fleming(!7> also suggested an undifferentiated category. The validity of these attempts has so far remained inconclusive. For example, Bertelsen and Gottesman (7) noted that at best, relatives of individuals with affective type schizoaffective disorder, or schizophrenic type schizoaffective disorder, showed only trends towards higher rates of affective disorder or schizophrenia, respectively. Similarly, Kendler et al.''I1 did not detect different rates of schizophrenia or affective illness in first-degree relatives of patients with schizoaffective disorder when the patients were subtyped into bipolar and depressive subgroups. Moreover, the subtypes did not predict differences in outcomes.

Conversely, a latent class analysis of psychotic patients from the Roscommon Study showed that most cases of DSM-IIIR schizoaffective disorder were categorized in either a bipolar schizomania class (n = 19), or in a schizodepression class (n = 13), rather than in schizophrenia (n = 1), major depression (n = 0), schizophreniform (n = 3), or hebephrenia (n = 3) classes/1,8,) Moreover, Winokur et al.'(1...9) provided indirect evidence for differential outcomes based on subtypes. In that study, subjects were diagnosed with Research Diagnostic Criteria for schizophrenia, affective disorder, or schizoaffective disorder, and evaluated at intake, 1 year later, and 6 years later. Several outcome measures were employed, including 39 Schedule for Affective Disorders and Schizophrenia items. Subjects were then divided into groups that had consistent affective diagnoses (including schizoaffective disorder, affective type) or consistent schizophrenic diagnoses (including schizoaffective disorder, schizophrenic type), at each of the three assessment times. A third group had inconsistent diagnoses. The results showed that recovery from psychosis was more common in the group with consistent diagnoses of affective disorder than it was in the group with consistent diagnoses of schizophrenia. The inconsistent group was intermediate, but was closer to the consistent affective group. Together, these studies show at least some recent support for the subtyping of schizoaffective disorder into mainly affective and mainly schizophrenic variants.

Other factors that may be prognostic of poor outcomes include poor interepisode recoveries, (!1) persistent psychotic symptoms in the absence of affective features, poor premorbid social adjustment, chronicity, and a higher number of schizophrenia-like symptoms.(5)

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