Subtype diagnosis in schizophrenia and its relation to neuropsychological and computerized tomography measures

Do neurobiological differences exist between paranoid and non-paranoid schizophrenia? Findings from the bipolar schizophrenia network on intermediate phenotypes study

Subtypes of schizophrenia, constructed using clinical phenomenology to resolve illness heterogeneity, have faced criticism due to overlapping symptomatology and longitudinal instability; they were therefore dropped from the Diagnostic Statistical Manual-5. Cognitive and imaging findings comparing paranoid (P-SZ) and non-paranoid (disorganized, residual and undifferentiated; NP-SZ) schizophrenia have been limited due to small sample sizes. We assessed P-SZ and NP-SZ using symptomatology, cognition and brain structure and predicted that there would be few neurobiological differences. P-SZ (n = 237), NP-SZ (n = 127) and controls (n = 430) were included from a multi-site study. In a subset of this sample, structural imaging measures (P-SZ, n = 133; NP-SZ, n = 67; controls, n = 310) were calculated using Freesurfer 6.0. Group contrasts were run using analysis of covariance, controlling for age, sex, race and site, p-values were corrected using False Discovery Rate (FDR) and were repeated excluding the residual subtype. Compared to NP-SZ (with and without the residual subtype), P-SZ displayed fewer negative symptoms, faster speed of processing, larger bilateral hippocampus, right amygdala and their subfield volumes. Additionally, NP-SZ (with residual subtype) displayed fewer depressive symptoms and higher left transverse temporal cortical thickness (CT) but NP-SZ without residual subtype showed lower GAF scores and worse digit sequencing compared to P-SZ. No differences in positive symptoms and functioning (global or social) were detected. Subtle but significant differences were seen in cognition, symptoms, CT and subcortical volumes between P-SZ and NP-SZ. While the magnitude of these differences is not large enough to justify them as distinct categories, the paranoid- nonparanoid distinction in schizophrenia merits further investigation.

Temporal information processing in short- and long-term memory of patients with schizophrenia

Cognitive deficits of patients with schizophrenia have been largely recognized as core symptoms of the disorder. One neglected factor that contributes to these deficits is the comprehension of time. In the present study, we assessed temporal information processing and manipulation from short- and long-term memory in 34 patients with chronic schizophrenia and 34 matched healthy controls. On the short-term memory temporal-order reconstruction task, an incidental or intentional learning strategy was deployed. Patients showed worse overall performance than healthy controls. The intentional learning strategy led to dissociable performance improvement in both groups. Whereas healthy controls improved on a performance measure (serial organization), patients improved on an error measure (inappropriate semantic clustering) when using the intentional instead of the incidental learning strategy. On the long-term memory script-generation task, routine and non-routine events of everyday activities (e.g., buying groceries) had to be generated in either chronological or inverted temporal order. Patients were slower than controls at generating events in the chronological routine condition only. They also committed more sequencing and boundary errors in the inverted conditions. The number of irrelevant events was higher in patients in the chronological, non-routine condition. These results suggest that patients with schizophrenia imprecisely access temporal information from short- and long-term memory. In short-term memory, processing of temporal information led to a reduction in errors rather than, as was the case in healthy controls, to an improvement in temporal-order recall. When accessing temporal information from long-term memory, patients were slower and committed more sequencing, boundary, and intrusion errors. Together, these results suggest that time information can be accessed and processed only imprecisely by patients who provide evidence for impaired time comprehension. This could contribute to symptomatic cognitive deficits and strategic inefficiency in schizophrenia.

Striatal mitochondria in subjects with chronic undifferentiated vs. chronic paranoid schizophrenia

Schizophrenia (SZ) is a heterogeneous disease with a spectrum of symptoms, risk factors, and etiology. Abnormalities in mitochondria, the energy-producing organelles of the cell, have been observed in mixed cohorts of subjects with SZ. The purpose of the present study was to determine if striatal mitochondria were differentially affected in two different DSM-IV subgroups of SZ. Postmortem striatal tissue was examined from normal controls (NC), chronic paranoid SZs (SZP), and chronic undifferentiated SZs (SZU). Tissue was processed for calbindin immunohistochemistry to identify striosomal compartments, prepared for electron microscopy and analyzed using stereological methods. In both caudate and putamen, the density of mitochondria in the neuropil was decreased in SZP compared to both NCs and SZU. In the putamen, both the SZP and the SZU subgroups had fewer mitochondria per synapse than did NCs. When examining patch matrix compartments, striatal compartments associated with different circuitry and function, only the matrix exhibited changes. In the caudate matrix, the SZP subgroup had fewer mitochondria in the neuropil than did the SZU and NCs. In the putamen matrix, the SZP had fewer mitochondria in the neuropil as compared to NCs, but not the SZU. The numbers of mitochondria per synapse in both the SZP and the SZU groups were similar to each other and fewer than that of NCs. A decrease in mitochondrial density in the neuropil distinguishes the SZP from the SZU subgroup, which could be associated with the symptoms of paranoia and/or could represent a protective mechanism against some of the symptoms that are less pronounced in this subtype than in the SZU subgroup such as cognitive and emotional deficits.

Do schizophrenia patients make more perseverative than non-perseverative errors on the Wisconsin Card Sorting Test? A meta-analytic study

The Wisconsin Card Sorting Test (WCST) is widely used to explore executive functions in patients with schizophrenia. Among other findings, a higher number of perseverative errors has been suggested to implicate a deficit in task switching and inhibitory functions in schizophrenia. Many studies of patients with schizophrenia have focused on perseverative errors as the primary performance index in the WCST. However, do schizophrenia patients characteristically make more perseverative than non-perseverative errors compared with healthy controls? We reviewed the literature where schizophrenia patients were engaged in the WCST irrespective of the primary goal of the study. The results showed that while both schizophrenia patients and healthy participants made more perseverative than non-perseverative errors, the contrast between perseverative and non-perseverative errors is higher in schizophrenia patients only at a marginal level of significance. This result suggests that schizophrenia patients do make a comparable number of non-perseverative errors and cautions against simplistic interpretation of poor performance of schizophrenia patients in WCST as entirely resulting from impairment in set-shifting or inhibitory functions.

Heterogeneity in functional status among older outpatients with schizophrenia: employment history, living situation, and driving

Schizophrenia and aging are both risk factors for deficits in independent functioning, yet relatively few studies have examined the level and predictors of functional status of older outpatients with schizophrenia. We compared employment history, current living situation, and driving status of 83 middle-aged and elderly outpatients with schizophrenia (mean age 59 years), and 46 demographically equivalent normal comparison subjects. We also examined the relationships of neuropsychological functioning and psychiatric symptoms to these aspects of everyday functioning. The schizophrenia patient group had consistently worse functional status than the normal comparison group, but 30% of the patients were employed at least 50% of the time during their post-schizophrenia-onset adult lives, 73% were living in a house or apartment and responsible for meeting most of their own daily needs, and 43% were current drivers. Severity of negative symptoms (but not that of positive symptoms) was inversely correlated with functional status. Worse performance on a neuropsychological battery was generally associated with worse functional status. These findings counter notions that functional impairment is inevitable in older schizophrenia patients, and highlight the importance of assessment of functional skills and possibly targeting them as a treatment focus.

A multimethod approach to assessing perseverations in schizophrenia patients

Perseverations have been associated with frontal lobe impairment and are often observed among schizophrenia patients. We assessed perseverations in schizophrenia patients (N = 71) using the Wisconsin Card Sorting Test (WCST) and a new Rorschach perseveration scale which yields three perseveration scores. We also compared the results of the schizophrenia patients with those of a normal comparison group (N = 71). We found that schizophrenia patients demonstrated a high number of perseverations on both the WCST and the Rorschach perseveration scale when compared to the normal comparison subjects. Among schizophrenia patients, WCST perseverative responses were significantly correlated with Rorschach-derived stuck-in-set perseverations, WAIS-R Vocabulary scores and negative symptom ratings. No significant differences in any of the measures of perseveration were found to be associated with diagnostic subtype. Finally, WCST and Rorschach measures for the schizophrenia and normal comparison participants were entered into a logistic regression. The WCST total errors and the three Rorschach perseveration measures resulted in the correct classification of 89.4% of the total cases, with a sensitivity of 91%, specificity of 91% and positive predictive power of 87.8%. These data provide evidence that perseverative behavior is widely observed in schizophrenia patients using a variety of instruments. The authors discuss the benefit of using multiple measures of perseveration in schizophrenia research.

Differential relationships between positive and negative symptoms and neuropsychological deficits in schizophrenia

This study assessed the relationships between positive and negative clinical symptoms and specific neuropsychological deficits in a group of stable schizophrenic patients.

METHOD

Thirty patients were assessed using the Positive and Negative Syndrome Scale (PANSS) for schizophrenia and a battery of cognitive tests. The PANSS assessments were done by a group of raters blind to the results of cognitive tests, while the cognitive tests were conducted by a different group of raters who remained blind to the PANSS scores.

RESULTS

We found that, although positive and negative symptoms showed a trend toward direct correlation with each other, they correlated with distinct cognitive deficits. Patients with higher negative scores had more perseverative responses, perservative errors, and completed fewer categories on the Wisconsin Card Sorting Test; they also experienced more difficulties on trail making and verbal fluency tests. On the other hand, positive symptoms were associated with poor performance on the Digit Span, particularly the Digit Span Forward.

CONCLUSIONS

Our findings are in agreement with previous reports that negative symptoms may be associated with poor performance on cognitive tests reflecting particularly frontal function. Positive symptoms, on the other hand, seem to be associated with poor attention, specifically of auditory type, and thus, possibly with dysfunction within the more widespread neural networks underlying attention. Our findings support the hypothesis that positive and negative symptoms may be associated with distinct neuropsychological deficits and thus with distinct neurological substrates and point to the need to address both positive and negative dimensions when studying schizophrenia.

Assessing declarative memory in schizophrenia using Wisconsin Card Sorting Test stimuli: the Paired Associate Recognition Test

The Paired Associate Recognition Test (PART) was developed to measure declarative memory using Wisconsin Card Sorting Test (WCST) stimuli, so that both tasks could be administered during functional neuroimaging to differentiate memory and executive function, and associated frontal and temporal lobe activation in schizophrenia. The current study was designed to compare PART and WCST performance in schizophrenic patients and to examine effects of medication and symptomatology. The PART, WCST, and standard declarative memory tasks were administered to 30 chronic schizophrenic patients and 30 matched healthy control subjects. Supporting task validity was the finding that patients were equally impaired on the PART and the WCST. Neuroleptics did not appear to affect performance. The effect of anticholinergic medication correlated negatively with WCST performance in a small subsample. Severity of schizophrenia-specific symptoms measured at intake on the Brief Psychiatric Rating Scale correlated negatively with performance on the WCST. These results support the application of the PART and WCST in future functional neuroimaging studies.

Neuropsychological deficit in newly diagnosed patients with schizophrenia or schizophreniform disorder

Forty-six patients with schizophrenia or schizophreniform disorder admitted to hospital for the first time were compared with 21 healthy volunteers on neuropsychological tests reflecting prefrontal and left respectively right hemisphere function. The patients with schizophrenia or schizophreniform disorder had a poorer performance on neuropsychological tests (such as Wisconsin Card Sorting) compared with healthy volunteers. Both left and right hemisphere seemed to be involved. Especially poor performance was found on somewhat complicated tests requiring ability of analysis, abstraction and memory, thus indicating dysfunction of prefrontal and temporohippocampal regions. Signs of sulcal enlargement and size of lateral ventricles on computed tomographic scan correlated with poor test performance on some tests both in patients and in healthy volunteers. No correlations were found between performance on neuropsychological test and negative symptoms.

Attentional asymmetry in schizophrenia: the role of illness subtype and symptomatology

1. Patients with undifferentiated and paranoid schizophrenia, and normal controls were compared using 2 versions of the covert orienting of attention procedure which evaluate exogenous (automatic) and endogenous (controlled) cuing mechanisms. 2. For both tasks, attentional performance varied with illness subtype, but in different ways. 3. On measures of automatic orienting undifferentiated patients showed evidence consistent with a mild right visual field deficit, while paranoid showed a reduction of inhibition-of-return, a mechanism which biases against returning to previously attended locations. 4. On measures of controlled orienting only the undifferentiated group showed the asymmetry of costs which has been the emphasis of most previous studies. The pattern of cost asymmetry was similar to that previously associated with prominent negative symptoms. Additionally, the magnitude of cost asymmetry correlated positively with negative symptoms in the overall patient group. 5. These findings show that systematically considering cue type and symptomatology are critical in interpreting varying patterns of performance by different groups of patients with schizophrenia on the covert orienting procedure. The implications of these findings for understanding the psychopathology of attention in schizophrenia and its neurobiological substrates are discussed.

Systematized delusions and neuropsychological function in paranoid and nonparanoid schizophrenia

We extended research originating with the Tsuang-Winokur criteria for paranoid and nonparanoid schizophrenia. To partially resolve problems of subtype instability, 41 consecutive admissions meeting DSM-III-R criteria for schizophrenia were subdivided according to whether they ever experienced prominent systematized delusions. Neuropsychological profiles for paranoid patients and nonparanoids with a history of systematized delusions were extremely similar. When combined, this 'systematized' group had significantly better general verbal ability and verbal memory than patients who never manifested systematized delusions. There was also a significant neuropsychological function-by-group interaction. The neuropsychological data suggested that systematized patients had better premorbid cognitive functioning as well as a greater discrepancy between premorbid verbal ability and current attentional functioning. No between-group differences were found on a measure of prefrontal-executive function, nor were there any neuropsychological differences between traditionally defined (DSM-III-R) paranoid and nonparanoid subgroups. This study suggests a possible shift in the dividing line between paranoid and nonparanoid subtypes and illustrates the potential value of neuropsychological data for refining psychiatric nosologies.

Relations between neuropsychological performance and brain morphological and physiological measures in monozygotic twins discordant for schizophrenia

Correlational approaches that examine the relation between neuropsychological measures and brain morphology or physiology in schizophrenia have yielded inconsistent results. This may be due in part to difficulties in ascertaining precisely to what degree each measure deviates from its genetically and environmentally determined potential level. We attempted to surmount this problem in a paradigm involving monozygotic twin pairs discordant for schizophrenia. In this paradigm, the difference score between the unaffected member and affected member of a twin pair should represent the degree of pathologic involvement irrespective of actual level. In correlating intrapair difference scores of anatomic structures measured from magnetic resonance imaging (n = 15) and prefrontal regional cerebral blood flow (rCBF) (n = 10) with cognitive abilities (after partialing IQ), we found strong associations between (1) the left hippocampus and a parameter of verbal memory, and (2) prefrontal rCBF with symptom scores and perseveration on the Wisconsin Card Sorting Test. These results support other research implicating medial temporal and prefrontal regions as important in the symptomatic expression and cognitive failures of schizophrenia. Overall, however, there was a relative paucity of significant associations between neuroanatomic and neurocognitive variables. This may have been due to the relatively restricted ranges of hippocampal size or cognitive ability found in this sample.

Relationship of prefrontal and temporal lobe MRI measures to neuropsychological performance in chronic schizophrenia

This preliminary study focused on the relationship between prefrontal and temporal lobe MRI measures and neuropsychological performance in chronic schizophrenia. Seventeen schizophrenic inpatients received an MRI and a neuropsychological test battery after clinical stabilization, on average 2 months after admission. The central finding was a significant inverse correlation between neurocognitive measures of prefrontal function and dorsolateral prefrontal cortex (DLPFC) area, strongest in the left hemisphere. Neurocognitive performance did not correlate significantly with orbital frontal area or total temporal lobe volume. The correlations of neuropsychological performance with total frontal volume and whole brain volume were generally not significant, although the pattern was similar to that associated with the DLPFC. Because a number of executive-attention and abstraction measures were significantly associated with the DLPFC, dysfunctions of this region may underlie a syndrome of cognitive dysfunctions. Long-term memory functions were also significantly correlated with the DLPFC, raising the possibility that recall memory defects in schizophrenia are, in part, associated with prefrontal contributions of attention, abstract reasoning, and executive function. This study needs replication with a larger sample of patients and more comprehensive volumetric morphometric analyses.

Phenylethylamine and schizophrenia

1. The evidence that phenylethylamine (PEA) plays a role in the etiology of schizophrenia is reviewed. 2. PEA shares structural and physiological similarities with the amphetamines, the administration of which can induce a schizophrenia-like psychosis. 3. While there are a number of reports of high urinary PEA excretion in schizophrenic patients, the measurement of PEA in other body fluids and the measurement of phenylacetic acid (the major metabolite of PEA) has resulted in inconsistent findings. 4. The use of neuroleptic medication is a major confounding variable in most of the clinical studies. If PEA does have a role in the etiology of schizophrenia, the mechanism may involve PEAs ability to amplify dopamine responses.

Abnormal processing of irrelevant information in schizophrenia: the role of illness subtype

In a study using a trial by trial version of the Stroop color naming task, we previously found that unmedicated patients with schizophrenia show a pattern of abnormal performance characterized by increased facilitation (speeding) of color-naming, color-congruent words but normal amounts of interference (slowing) of color-naming, color-incongruent words (Carter et al., 1992). Since a similar finding had recently been reported in patients with Parkinson's disease, we suggested that this finding was consistent with hypotheses about the neurobiological substrates of cognitive impairment that draw upon parallel patterns of cognitive performance in the two illnesses. We now report results from an enlarged group of unmedicated patients with schizophrenia that extend our original finding by allowing us to evaluate the role of illness subtype in abnormal performance on the Stroop task. We found that patients with the undifferentiated subtype of the disorder account for the increased Stroop facilitation effect. Patients with the paranoid subtype show their own pattern of abnormal performance, with normal amounts of facilitation and increased interference. These findings are consistent with the results of other studies which suggest that illness subtype is an important source of variability in studies of cognitive functioning in schizophrenia.

The Kallmann's syndrome variant (KSV) model of the schizophrenias

The KSV model of the schizophrenias proposes that up to 70% of schizophrenics have a pathogenic allele, or abnormal expression, of the KALIG-1 gene which is located at Xp22.3. This gene encodes a nerve-cell adhesion molecule (N-CAM) like protein, and is deleted in 66% of patients with Kallmann's syndrome, anosmia with secondary hypogonadism. Although superficially distinct, the schizophrenias and Kallmann's syndrome show numerous parallel trait defects which occur with a similar sex distribution. These defects are usually more profound in Kallmann's syndrome. Occasionally, Kallmann's patients exhibit additional defects, such as ichthyosis, which are due to the further deletion or translocation of adjacent genes. Since schizophrenics exhibit virtually all known trait defects in Kallmann's except these, it suggests that the aberrant genes are defective, but not deleted in schizophrenia. It also appears that compensatory mechanisms, involving serine proteases, are active in schizophrenia, which largely preserve fertility, but at the expense of an increased vulnerability to develop a psychosis by an episodic disruption of the blood-CSF barrier. Consequently, schizophrenia is rare in Kallmann's patients, while most schizophrenics are capable of reproduction.

Wisconsin Card Sorting Test: an indicator of vulnerability to schizophrenia?

The Wisconsin Card Sorting Test (WCST) is a neuropsychological test, hypothesized to be an indicator of dorsolateral prefrontal cortex (DLPFC) functioning. The performance of schizophrenic patients in our sample (off medication) was worse than the performance of healthy controls in all variables of the WCST, including perseverative responses (PR) as well as non-perseverative responses (NPR). The rate of perseverative and non-perseverative responses was neither a function of the severity of the illness (measured by SANS/SAPS scales) nor the duration of the disease. Healthy siblings of schizophrenic probands revealed more perseverative responses than healthy controls, but did not show any difference with respect to the non-perseverative responses. This finding suggests that the difficulty to shift a cognitive set, reflected by the frequency of perseverative responses, is in favor of the WCST as a vulnerability marker for schizophrenia, whereas non-perseverative responses presumably indicate a state, but not a trait marker of the disease. However, the usefulness of this indicator may be limited by its association with age, which is worthy of being studied in closer detail.