A neuropsychological perspective on dual diagnosis.

The purpose of this study was to investigate whether patients experiencing both a major psychiatric disorder and a concurrent substance abuse problem (dual diagnosis) manifest greater neuropsychological dysfunctions than patients experiencing a major psychiatric disorder alone. Differences in diagnostic variability and fluidity between dual diagnosis and non-dual diagnosis patients and the occurrence of polysubstance abuse among the dual diagnosis patients were also investigated. The hypotheses were tested by retrospectively reviewing the psychiatric records of 50 dual diagnosis patients and comparing them to 36 chronically hospitalized non-dual diagnosis psychiatric patients. Results revealed that dual diagnosis patients manifested significantly greater neuropsychological impairments than non-dual diagnosis patients and that dual diagnosis patients showed a greater range of diagnoses and diagnostic fluidity than non-dual diagnosis patients. Results also revealed that over one-half of the dual diagnosis patients abused a variety of different substances. An etiological role of neuropsychological dysfunction in the development of the dual diagnosis syndrome in at least a subgroup of dual diagnosis patients is suggested. More specifically, it is suggested that the neuropsychological dysfunctional pattern that is described may represent an organic substrate of a nonspecific vulnerability to developing both (atypical) psychoses and (poly) substance abuse.