Sources of heterogeneity in schizophrenia: the role of neuropsychological functioning.

Although schizophrenia is often characterized as a heterogeneous disorder, efforts to validate stable and meaningful subtypes have met with limited success. Thus, the issue of whether schizophrenia reflects a continuum of severity or a number of discrete subtypes remains controversial. This review evaluates efforts to establish subtypes based upon a model that includes causes, characteristics, and course and outcomes of heterogeneity. Emphasis is placed on empirical classification studies utilizing cognitive tests or symptom rating scales, sometimes in conjunction with neuroimaging procedures. Results of recent cluster analytic studies are reviewed that produced evidence of four or five clusters, varying in level and pattern of performance. Although this research typically generated meaningful subtypes, it was often the case that there was little correspondence between subtyping systems based upon cognitive function and those based upon symptom profile. It was concluded that there may be different mechanisms for producing cognitive and symptomatic heterogeneity, and that diversity in presentations of schizophrenia reflects a combination of continuities in severity of the disorder with a number of meaningful and stable subtypes.

Relations between cognitive and symptom profile heterogeneity in schizophrenia.

Although numerous studies have consistently revealed cognitive heterogeneity in schizophrenia, the relationships between such heterogeneity and clinical phenomenology are not clear. Clusters derived from cognitive heterogeneity studies may or may not be associated with symptom profile or severity of illness. The purpose of this study was to examine the relationship between cognitive heterogeneity and demographic and clinical phenomenological measures. We examined cognitive heterogeneity in schizophrenia by empirically deriving clusters of patients based upon WAIS-R subtest scores and then analyzed the way in which these clusters related to demographic and symptom variables and to DSM-III-R diagnostic subtypes. Four cognitive clusters were identified that were consistent with previous research. These clusters were differentiated on the basis of educational level and occupational status but not on the basis of symptom profile, severity, or DSM-III-R subtypes. Results suggest that cognitive measures are independent of severity of the disorder and phenomenological symptom presentation in these subgroups of schizophrenic patients.

Confirmatory factor analysis of the WAIS-R in patients with schizophrenia.

Although factor scores are commonly used to interpret the Weschsler Adult Intelligence Scale--Revised (WAIS-R), the WAIS-R factor structure has not been investigated in patients with schizophrenia. We used confirmatory factor analysis (CFA) to examine five latent construct models in 169 males with schizophrenia. The WAIS-R standardization sample (ages 35-44; n = 250) was used as a comparison group. For both groups, all model fit indexes used to determine model adequacy supported models composed of Verbal Comprehension (VC), Perceptual Organization (PO) and Freedom from Distractibility (FFD) factors. However, the Digit Symbol subtest loaded on both the PO and FFD factors for patients with schizophrenia but only on the FFD factor for the WAIS-R standardization sample. Patients with schizophrenia performed significantly worse on the FFD and PO factors compared to the VC factor, reflecting the well-characterized attention and problem solving deficits associated with schizophrenia. Also, patients with schizophrenia performed significantly worse than the WAIS-R sample on all factors. These results provide support for the validity of the WAIS-R factors in patients with schizophrenia.

A comparison of clustering solutions for cognitive heterogeneity in schizophrenia.

A cluster analytic solution based upon a battery of tests consisting of the Halstead Category and Tactual Performance Tests, the Trail Making Test, and the Wisconsin Card Sorting Test was compared with a solution based on the subtests of the Wechsler intelligence scales, utilizing a sample of 221 schizophrenic patients. Both analyses permitted four-cluster solutions, and we found a weak but significant degree of association between solutions. Examination of external validity of the two solutions revealed stronger associations with clinical variables for the Wechsler-scale-based solution. The major conclusions were that the existence of cognitive heterogeneity in schizophrenia exists across a broad range of abilities, and appears to reflect a combination of continuity of ability level and existence of possible subtypes requiring further neuropsychological and neurobiological verification.

Cognitive rehabilitation of chronic alcohol abusers.

The current literature suggests that individuals who chronically abuse alcohol exhibit a wide variety of cognitive deficits resulting from cerebral dysfunction that is either directly or indirectly related to their alcohol consumption history. Cognitive deficits have been hypothesized as having implications for standard alcohol treatment efficacy as they may directly affect cognitively impaired individuals' abilities to utilize various treatment modalities. Although evidence is accumulating that suggests this is actually the case, the majority of alcohol treatment programs neither directly consider the impact cognitive deficits have on treatment efficacy nor do they employ cognitive rehabilitation treatment strategies to remediate identified cognitive deficits. Few studies exist that investigate the remediability of neurobehavioral deficits or the efficacy of integrating cognitive rehabilitation strategies into more traditional treatment programs. Empirical investigations conducted to date indicate that some cognitive deficiencies secondary to alcoholism are amenable to cognitive rehabilitation and this remediation is generalizable. Rigorous well-controlled treatment outcome investigations are needed in order to determine the efficacy of cognitive rehabilitation techniques in naturalistic settings using ecological outcome measures. Also, emphasis should be placed on integrating cognitive rehabilitation techniques with proven efficacy into traditional alcoholism treatment programs.