Differential Diagnosis of Depression in the Course of Schizophrenia

Schizoaffective Depression
Conceptually, the diagnosis of schizoaffective disorder pertains when the patient’s presentation of the full depressive syndrome coincides with the florid psychotic syndrome in patients who also have been psychotic in the absence of an affective syndrome. This situation has been defined differently according to various diagnostic schemes (Coryell et al. 1990; Levitt and Tsuang 1988; Taylor 1992), the application of which can cause some variation in the exact boundary between “depression in schizophrenia” and “schizoaffective depression.”

The diagnosis of schizoaffective disorder opens up a set of treatment options that may be valuable but that take us beyond the scope of the present chapter (Siris 1996; Siris and Lavin 1995). The issue of schizoaffective disorder, of course, also enters into the consideration of postpsychotic depression in schizophrenia, because postpsychotic depression occurs in schizoaffective disorder as well. There have been no specific studies of the latter situation; clinical trials have essentially collapsed the latter group of patients with the former under the assumption that the same interventions are applicable in these two circumstances.

Depression as the Expression of a Biological Diathesis in the Course of Schizophrenia
Finally, after the other elements of the differential diagnosis noted earlier in this section have been ruled out, we are left with the possibility of a depression based on a biological diathesis occurring in an individual otherwise correctly diagnosed with schizophrenia. The determination of this issue, at least at the present time, is inexact, since there is no available direct biological way to ascertain the presence of a biological diathesis for depression-or, for that matter, schizophrenia. Specifically, there is no biopsy, electrical test, chemical test, radiological test, genetic marker, or even autopsy finding that can definitively establish such a psychiatric diagnosis.

Instead, we are limited to phenomenological descriptors and patients’ own accounts of their subjective states in arriving at our diagnoses. Indeed, patients’ responses to medications have frequently been used historically as validators for the symptom lists we have come to employ today to establish the boundaries of diagnoses such as depression and schizophrenia-a use of “predicate logic” that clinicians would readily recognize as flawed if they saw a patient using it to arrive at an important conclusion.

On the other hand, since clinicians are fundamentally interested in identifying the most sensible treatment for suffering dysfunctional individuals when they employ a diagnostic scheme, this approach has validity in that appropriate treatments may be suggested even if the logic might be flawed and the underlying biological assumptions might not be correct. The discussion of treatment issues that occurs later in this chapter certainly should be interpreted with this in mind.

Samuel G. Siris, M.D.


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