An attempt to study intellectual deterioration by premorbid and psychotic testing

Neuropsychological decline in schizophrenia from the premorbid to the postonset period: evidence from a population-representative longitudinal study

OBJECTIVE

Despite the widespread belief that neuropsychological decline is a cardinal feature of the progression from the premorbid stage to the chronic form of schizophrenia, few longitudinal studies have examined change in neuropsychological functioning from before to after illness onset. The authors examined whether neuropsychological decline is unique to schizophrenia, whether it is generalized or confined to particular mental functions, and whether individuals with schizophrenia also have cognitive problems in everyday life.

METHOD

Participants were members of a representative cohort of 1,037 individuals born in Dunedin, New Zealand, in 1972 and 1973 and followed prospectively to age 38, with 95% retention. Assessment of IQ and specific neuropsychological functions was conducted at ages 7, 9, 11, and 13, and again at age 38. Informants also reported on any cognitive problems at age 38.

RESULTS

Individuals with schizophrenia exhibited declines in IQ and in a range of mental functions, particularly those tapping processing speed, learning, executive function, and motor function. There was little evidence of decline in verbal abilities or delayed memory, however, and the developmental progression of deficits in schizophrenia differed across mental functions. Processing speed deficits increased gradually from childhood to beyond the early teen years, whereas verbal deficits emerged early but remained static thereafter. Neuropsychological decline was specific to schizophrenia, as no evidence of decline was apparent among individuals with persistent depression, children with mild cognitive impairment, individuals matched on childhood risk factors for schizophrenia, and psychiatrically healthy individuals. Informants also noticed more cognitive problems in individuals with schizophrenia.

CONCLUSIONS

There is substantial neuropsychological decline in schizophrenia from the premorbid to the postonset period, but the extent and developmental progression of decline varies across mental functions. Findings suggest that different pathophysiological mechanisms may underlie deficits in different mental functions.

Does operational diagnosis of schizophrenia significantly impact intellectual deficits in psychotic disorders?

BACKGROUND

Evidence suggests that, as a group, patients with schizophrenia have intellectual deficits that may precede the manifestation of psychotic symptoms; however, how successfully intelligence tests are able to discriminate schizophrenia from other psychotic disorders has yet to be investigated in detail.

METHODS

Using Wechsler Adult Intelligence Scale-Revised (WAIS-R) data for 55 inpatients with schizophrenia and 28 inpatients with non-schizophrenic psychotic disorders (NSPD) (schizophreniform disorder, brief psychotic disorder, delusional disorder, psychotic disorder due to a general medical condition, and psychotic disorders not otherwise specified), intelligence performance was compared between schizophrenia and NSPD and among different subtypes of schizophrenia.

RESULTS

There were no significant differences in intelligence quotient (IQ), verbal IQ (VIQ) and performance IQ (PIQ) discrepancy, and subtest scores of WAIS-R between the patients with schizophrenia and those with NSPD. These diagnostic groups were not discriminated well by any WAIS-R variables. Schizophrenia patients with prominent negative symptoms, on the other hand, had a significantly larger IQ discrepancy (VIQ > PIQ) than those without prominent negative symptoms and NSPD patients. Intelligence performance in schizophrenia did not differ with respect to diagnostic subtypes and longitudinal courses.

CONCLUSIONS

The current study failed to show diagnostic usefulness of WAIS-R in discriminating schizophrenia and other psychoses. A diagnosis of schizophrenia does not significantly impact intellectual deficits in psychotic disorders.

Memory and intellectual deficits do not decline with age in schizophrenia

Cognitive deficits in schizophrenia are reported to be more consistent with a static encephalopathy than a dementing disorder. This study investigates memory and intellectual decline in 62 chronic schizophrenic subjects using the Wechsler Adult Intelligence Scale-Revised (WAIS-R), the Rivermead Behavioural Memory Test and the National Adult Reading Test (NART) in a cross-sectional study using five age cohorts (18-29, 30-39, 40-49, 50-59 and 60-69 years of age) and then by two cohorts (young: 18-39; older: 40-69). A second method of investigating intellectual decline was implemented by estimating the discrepancy score between WAIS-R (current IQ) and NART (premorbid IQ) for each subject. No significant differences were found in WAIS-R Full Scale. Verbal and Performance IQ and memory functioning across the five age cohorts (and when using two age groups). A significant difference in test scores was found using the Picture Completion and Digit Symbol subtests of the WAIS-R. The differences were not related to age or duration of illness. No significant difference in scores were evident in the remaining WAIS-R subtests. These results support previous findings that schizophrenia is more consistent with a static encephalopathy than a dementing disorder and that intellectual and memory function does not markedly decline with age.

Estimation of premorbid intelligence in schizophrenia

To determine whether the National Adult Reading Test (NART) would provide a valid estimate of premorbid intelligence in schizophrenia, two schizophrenic samples were recruited, one consisting of 35 patients resident in long-stay wards, the other of 29 patients normally resident in the community. Schizophrenic patients were individually matched for age, sex, and education with a healthy, normal subject. Both schizophrenic samples scored significantly lower on the Wechsler Adult Intelligence Scale (WAIS) than their respective control groups. NART-estimated IQ did not differ significantly between the community-resident schizophrenics and their controls, suggesting that the NART provides a valid means of estimating premorbid intelligence in such a population. NART-estimated IQ was significantly lower in the long-stay sample than in their controls. Although low NART scores in this latter sample could be a valid reflection of low premorbid IQ, the alternative explanation that NART performance was impaired by onset of the disease cannot be ruled out.

Age disorientation in chronic schizophrenia is not associated with pre-morbid intellectual impairment or past physical treatment

Forty-two long-stay hospital patients with chronic schizophrenia were divided into age and sex-matched groups with and without temporal disorientation, and assessed for premorbid academic performance and past physical treatment. The schooling of schizophrenic patients who had cognitive impairment, as identified by gross temporal disorientation, did not differ from those who were cognitively intact. The groups did not differ in past history of ECT, insulin coma, neuroleptic treatment, or psychosurgery. Patients with age disorientation were on lower mean doses of neuroleptic or anticholinergic medication. Gross cognitive impairment thus appears to occur in the course of the disease and is not due to physical treatment.

Intellectual deterioration and personality decompensation in schizophrenia

The Army General Classification Test (AGCT) and the MMPI were administered to schizophrenic inpatients (N = 50) with initially high (mean standard score = 115) and low (77) intelligence at two timepoints separated by an average of 14 years. The Arithmetic scores of the more intelligent group declined significantly with time, but significant changes did not appear on the Vocabulary or Spatial Aptitude scores of that group. No significant mean changes appeared in the low-IQ sample. The high-IQ group's Arithmetic section deterioration resulted from an increased error rate, not a drop in speed. No changes beyond those attributable to chance appeared on the MMPI scales. The results suggest that an intellectual decline limited to certain skills and to a subset of subjects occurs in schizophrenia and that the deterioration is not attributable to personality decompensation as defined by the MMPI. Because these findings appear to contrast with most previous research in this area, they should be considered tentative until confirmed by independent studies.

[Testing chronic schizophrenics with the HAWIE test (author's transl)]

The HAWIE test was given to 70 hospitalized chronic schizophrenics with the aim of 1. determining the intelligence level of the patients; 2. finding out to what extent possible changes in intelligence achievement are due to the sickness, the treatment, or the hospitalism. The test results were compared with the norm; they were also evaluated within the sample group, as a function of the amount of time spent in the institution. Compared with the norm, the intelligence level of the patients was low; one contributing factor was the duration of the hospitalization. In connection with the length of hospitalization, a deterioration of the non-verbal IQ was found; this is to be interpreted within the conceptual framework of the deprivation syndrome (hospitalism). Our test results have been compared with those of other studies focusing on the special HAWIE problem.