|Year : 2011 | Volume
| Issue : 2 | Page : 107-114
A comparative study of cognitive deficits in patients with delusional disorder and paranoid schizophrenia
Sandeep Grover, Ritu Nehra, Gaurav Bhateja, Parmanand Kulhara, Suresh Kumar
Department of Psychiatry, Postgraduate Institute of Medical Education and Research, Chandigarh, India
|Date of Web Publication||16-Oct-2012|
Department of Psychiatry, Postgraduate Institute of Medical Education and Research, Chandigarh - 160 012
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: Very few studies have evaluated the neurocognitive functions of patients with persistent delusional disorder. Aim: To study the neurocognitive profile of patients with delusional disorder and compare it with those of patients with paranoid schizophrenia and healthy control subjects. Materials and Methods: Attention concentration, executive functions, memory, and IQ were assessed in 20 patients with delusional disorder and were compared with 20 patients with paranoid schizophrenia and 20 healthy controls. All three groups were matched on age, sex, and level of education. The two patient groups were also matched on duration of illness. Results: In general, patients with delusional disorder performed worst than healthy controls and patients with paranoid schizophrenia performed in between the other two groups. Compared with healthy controls, both patients with delusional disorder and patients with paranoid schizophrenia were significantly impaired on different tests of attention and visual learning and memory. Compared with patients with paranoid schizophrenia, patients with delusional disorder had more impairment different tests of attention, visual learning and memory, verbal working memory, and executive functions. Conclusion: Patients with delusional disorder exhibit cognitive dysfunctions that are very similar to schizophrenia, but are more severe in intensity. The resemblance of cognitive profiles suggests that the two disorders may have similar etiological basis.
Keywords: Cognitive deficits, delusional disorder, schizophrenia
|How to cite this article:|
Grover S, Nehra R, Bhateja G, Kulhara P, Kumar S. A comparative study of cognitive deficits in patients with delusional disorder and paranoid schizophrenia. Ind Psychiatry J 2011;20:107-14
Once viewed as rare so as not to warrant a separate classification, paranoid disorder now renamed as delusional disorder (DD) has emerged as a focus of clinical research in recent years. Better definition and growing literature about this disorder have revitalized efforts to characterize, understand, and treat this condition.
Although a large database exists with respect to neurocognitive deficits in schizophrenia,  very few studies have evaluated neurocognitive disturbances in patients with DD. Herlitz and Forsell  examined memory functions in two groups of elderly adults with and without suspected DD and reported that elderly adults with suspected DD had mild episodic memory deficits in the absence of other cognitive dysfunctions compared with normal subjects. Studies that have compared neurocognitive functions of patients with DD with patients with schizophrenia have come up with inconsistent findings. Some suggest that neurocognitive impairments, although not statistically significant, are somewhat lower in patients with DD as compared with patients with schizophrenia,  whereas a study showed that patients with DD had a greater mean on the Halstead-Reitan Impairment Index as compared with patients with schizophrenia.  In one of the earliest study, Tarter and Perley  studied patients with suspected DD and paranoid schizophrenia with the Rod and Frame Test, Size Estimation Test, and Minnesota Multiphasic Personality Inventory (MMPI) and showed that the two groups differed significantly in MMPI, but no difference was found in other two perceptual tests. Evans et al. reported nonsignificantly lower impairment, while Jeste et al. reported greater impairment on the Halstead-Reitan test in patients with DD. A study on patients with erotomania, a specific subtype of DD, reported deficits in cognitive flexibility, associative learning, and deficits in verbal and visuospatial skills.  A study that assessed memory functions of patients with delusional misidentification syndrome reported significantly lower performance on tests of memory compared with healthy controls.  A recent study reported poor executive functioning in patients with DD compared with healthy controls. 
Thus, research in the area of neurocognitive functioning in patients with DD appears to be meager. In this background, the present study aimed to study the neurocognitive profile of patients with DD and compared it with the neurocognitive profile of patients with paranoid schizophrenia and of healthy control subjects. An attempt was also made to study the sociodemographic and clinical correlates of neurocognitive functions in patients with DD.
| Materials and Methods|| |
This study was carried out in a multispecialty tertiary care hospital in North India. Study population was selected from the patients either attending the psychiatry outpatient clinic or admitted to the inpatient unit.
The study included two patients groups: Group 1 - 20 'stable' patients with DD; Group 2 - 20 'stable' patients with paranoid schizophrenia. The diagnosis was based on ICD-10 Diagnostic Criteria for Research criteria. 
Inclusion and exclusion criteria
To be included in the study, the patients were required to be of age 20-60 years, of either sex, and have at least 8 years of formal education. The duration of illness of at least 1 year or more was an inclusion criterion, and the patients were required to be clinically stable for at least 3 months. Clinical stability of 3 months was defined as no exacerbation of symptoms, as per patient's and relative's account, and medical records and hike in the dose of psychotropic medications not more than 50% dosages in the last 3 months. Patients with major chronic physical illness (cerebrovascular accident, epilepsy, head injury, demyelinating diseases, etc.), organic mental disorder, and substance dependence/abuse except tobacco; patients having diagnosed and/or self-reported visual and/or auditory impairment; patients who had received electroconvulsive therapy in last 6 months; and patients with comorbid psychiatric syndromes except 'Cluster A' Personality disorder as per diagnostic and statistical manual-4 th revision (DSM-IV)  were excluded.
Healthy control group
The healthy control group of 20 subjects comprised 'nonblood relative' attendants of patients. Healthy control subjects were also required to be of age 20-60 years, of either sex, have at least 8 years of formal education, including English and Hindi in the syllabus, have no history of any psychiatric illness or treatment for psychiatric disorder, and have no history of chronic physical illness. Further healthy subjects were screened on General Health Questionnaire (GHQ-12), , and those who scored 3 or more were excluded. Subjects with major chronic physical illness (cerebrovascular accident, epilepsy, head injury, demyelinating diseases, etc.), substance dependence/abuse except tobacco, having diagnosed and/or self-reported visual and/or auditory impairment, and those with a family history of psychotic disorder were excluded.
All three groups were matched on age, sex, and level of education. The two patient groups were also matched on duration of illness.
All patients were rated on the Brief Psychiatric Rating Scale (BPRS)  and Montgomery Asberg Depression Rating Scale (MADRS). 
All the subjects including controls were assessed for the handedness on Edinburgh Handedness Inventory (EHI).  This inventory provides a standard of comparison in neurocognitive testing.
The neurocognitive domains assessed included the following.
Sustained attention and focused attention were assessed by using the Digit Vigilance Test,  and Colour Trails Part I and Part II  were used to assess the mental flexibility.
Visual working memory and verbal working memory  were assessed using one back and two back tasks. The verbal memory was assessed using 30 randomly arranged consonants for each level, which were read out to the subject. In the case of visual working memory, the stimulus consisted of a black dot presented in random locations. The number of correct responses, omissions, and commissions were noted down.
Executive functions were assessed by using the Tower of London test  for assessing specifically the person's ability to plan and anticipate their actions, and the Wisconsin Card Sorting Test (WCST)  was used to assess the ability to shift cognitive strategies in response to changing environmental contingencies.
Learning and memory
Verbal learning and memory were assessed by using Rey's Auditory Verbal Learning Test,  which specifically taps memory span, new learning, and recognition. Visuospatial constructional ability and visuospatial memory were assessed by using the Rey's Complex Figure Test. 
Verbal comprehension was assessed by using the Token Test.  It is a sensitive measure of receptive aphasia and also developmental aphasia. The commands are of increasing length and complexity.
The intelligence quotient (IQ) was assessed by using the Bhatia Battery of Performance Tests of Intelligence - Short Scale.  It consists of Koh's Block Design Test and Pass Along Test. Both reaction times and accuracy of performance are scored. In this test, the total IQ of the patient is calculated by extrapolation/interpolation of the PQ scores. Raw scores were initially calculated and then converted to weighted scores as per the norms appropriate to age and level of education. IQ is calculated by the formula IQ = 2.5 × (sum of weighted scores on Koh's Block Design Test and Pass Along Test).
The subjects fulfilling the selection criteria were approached. After obtaining the written informed consent, their sociodemographic and clinical details were recorded and the patients were rated on BPRS and MADRS. The neurocognitive tests were subsequently administered in the following invariant sequence: Digit Vigilance Test, Colour Trails Test, Working Memory Tests, Tower of London test, WCST, Token Test, Rey's Auditory Verbal Learning Test, Rey's Complex Figure Test, and Bhatia Short Scale-Revised. The complete evaluation took approximately 3-3.5 h.
Approval and consent
This study was approved by the institute's ethics committee, and all patients and healthy control group subjects were recruited after obtaining written informed consent.
Descriptive statistics in terms of percentages was used for categorical variables such as sociodemographic characteristics and clinical characteristics. The cognitive function scores of different groups (DD, schizophrenic controls, and normal controls) were compared by using analysis of variance and chi-square tests. The relation of sociodemographic variables and clinical characteristics with cognitive function scores in both patient groups was ascertained by using various comparison and correlation statistics.
| Results|| |
The sociodemographic profile of the three groups is presented in [Table 1]. The majority of the patients and the healthy control subjects were Hindus, middle aged, married and were from nuclear families and urban backgrounds.
As shown in [Table 2], there was no significant difference between the two patients groups on clinical variables such as duration of illness, age of onset, duration of treatment, lag period before the starting of the treatment, BPRS score, and MADRS score. [Table 2] shows clinical and treatment characteristics of the patient groups.
All subjects with paranoid schizophrenia group were right handed, 95% subjects with DD were right handed, and 90% of the normal controls were right handed, and the difference between the three groups was not significant (chi-square value 2.10; P>0.05).
As shown in [Table 3], there was no statistically significant difference between the three groups on the Digit Vigilance Test. On color trail '1' and '2', the DD group took maximum time and differed significantly from the paranoid schizophrenia group and the normal control group. However, there was no statistically significant difference between the paranoid schizophrenia group and the normal control group. In addition, on color trial '1', only DD group committed significantly more number of errors compared with normal controls but did not differ significantly from the paranoid schizophrenia group.
|Table 3: Neurocognitive profile of patients with DD, patients with paranoid schizophrenia, and healthy|
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On the visual working memory test, patients in the DD group had significantly fewer hits compared with normal controls. Patients with paranoid schizophrenia performed in between the DD and the normal control group. Furthermore, on two-back visual test, patients with DD and schizophrenia committed significantly more number of errors compared with the normal control group. However, the two patient groups did not differ significantly.
On the Tower of London test, three groups did not differ significantly, except that patients in the DD group but not in the schizophrenia group solved significantly lower number of problems with minimum moves compared to healthy controls.
There was a significant difference between the three groups on the Wisconsin Card Sorting Test and Token Test. In general, patients with DD performed the worst; healthy controls performed the best; and patients with paranoid schizophrenia performed in between the other two groups. However, there was no significant difference in the number of categories completed by patients with paranoid schizophrenia and normal controls on WCST.
On the test of auditory verbal learning and memory, patients in the DD group differed significantly from healthy controls on the percentage of retention.
On Rey's Complex Figure Test, when asked to copy the complex figure, performance of normal controls was better than that of patients with DD. On the same test, both patient groups performed significantly poorly compared with normal controls on immediate and delayed recall. However, the two patient groups did not differ significantly.
On the test of intelligence, all the three groups did not differ significantly, except that patients with DD had significantly lower PQ as compared with normal controls.
Neurocognitive functions after controlling for IQ
When the three groups were compared on various neurocognitive tests, after controlling for intelligence, similar differences persisted except that a significant difference emerged on the following: between DD and paranoid schizophrenia group on the mean number of second move on the Tower of London test and between paranoid schizophrenia group and normal controls on the mean number of third move on the Tower of London test. Furthermore, the significant difference between patients with DD and normal controls on the percentage retention on the Auditory Verbal Learning Test disappeared.
Correlates of neurocognitive functions Sociodemographic variables and neurocognitive functions
For assessing the correlations between neurocognitive functions and various sociodemographic and clinical variables, data of the three groups were pooled. It was seen that age had a significant positive correlation with time to complete color trails '1' (Pearson correlation coefficient value 0.320; P<0.05) and '2' (Pearson correlation coefficient value 0.298; P<0.05) test. Higher levels of education had negative correlation with time taken to complete the digit vigilance (Pearson correlation coefficient value -0.363; P<0.01), color trails '1' (Pearson correlation coefficient value -0.411; P<0.001), and color trails '2' (Pearson correlation coefficient value -0.423; P<0.001) tests. Furthermore, higher level of education was associated with significantly more number of hits on two-back visual test (Pearson correlation coefficient value 0.292; P<0.05), one-back verbal test (Pearson correlation coefficient value 0.320; P<0.05), and two-back verbal test (Pearson correlation coefficient value 0.337; P<0.01). Higher levels of education was associated with significantly fewer number of mistakes on two-back visual errors (Pearson correlation coefficient value -0.358; P<0.01), one-back verbal errors (Pearson correlation coefficient value -0.438; P<0.001), and two-back verbal errors (Pearson correlation coefficient value -0.371; P<0.01).
Higher level of education was also associated with significantly fewer number of percentage errors (Pearson correlation coefficient value -0.326; P<0.05), perseverative responses (Pearson correlation coefficient value -0.257; P<0.05), perseverative errors (Pearson correlation coefficient value -0.275; P<0.05), and percent perseverative errors (Pearson correlation coefficient value -0.263; P<0.05) on WCST and was also associated with a higher number of categories completed (Pearson correlation coefficient value 0.351; P<0.01).
Higher level of education was also associated with better scores on the token test (Pearson correlation coefficient value 0.257; P<0.05), larger number of hits on the Auditory Verbal Learning Test (Pearson correlation coefficient value 0.279; P>0.05), higher percent retention on the Auditory Verbal Learning Test (Pearson correlation coefficient value 0.260; P>0.05), fewer number of errors on the Auditory Verbal Learning Test (Pearson correlation coefficient value 0.374; P>0.01), better performance on RCFT copy task (Pearson correlation coefficient value 0.452; P<0.001), RCFT immediate recall (Pearson correlation coefficient value 0.385; P>0.01), RCFT delayed recall (Pearson correlation coefficient value 0.432; P>0.001), performance intelligence quotient (Pearson correlation coefficient value 0.452; P>0.001), and intelligence quotient (Pearson correlation coefficient value 0.464; P>0.001).
There was no significant relation between neurocognitive functioning and sex and occupation except that employed subjects took significantly less mean time (t value 2.04; P>0.05) and mean moves (t value 2.15; P>0.05) to complete five moves problem on the Tower of London test than did unemployed subjects. Furthermore, employed subjects completed significantly more categories of WCST than did unemployed subjects (t value 2.34; P>0.05).
Clinical variables and neurocognitive functions
The association between clinical variables and neurocognitive functions was studied by pooling the data of both the patient groups. There was no relation between age of onset and any of the neurocognitive functions. As shown in [Table 4], the maximum number of correlations emerged between BPRS score and findings on the Tower of London test and the lag period before seeking treatment was associated with some of the subtests of the Tower of London test and perseverative responses on WCST. As shown in [Table 3], patients with higher duration of illness took significantly more time in completing the Digit Vigilance Test, had significantly less hits on the two-back verbal test, scored significantly less on the token test, scored significantly less on the immediate and delayed recall of complex figure test. Patients with longer lag period for treatment committed significantly more errors on color trails '2' test, had significantly less hits on the two-back verbal test, had significantly more perseverative responses on WCST, and scored significantly less on the token test. Patients with higher MADRS score had significantly less number of problems solved with minimum moves three moves problem on the Tower of London test and took significantly more moves to complete four moves problem on the Tower of London test.
|Table 4: Clinical profile and neurocognitive tests in the patient groups|
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| Discussion|| |
Neurobiological mechanisms underlying schizophrenia have been investigated more vigorously than those in other psychotic disorders, particularly DD. One aspect of neurobiology is the study of neurocognitive functions. According to existing literature, few studies have specifically assessed neurocognitive functions in patients with DD. ,,,,,
No study seems to have compared neurocognitive functions in DD with patients with paranoid schizophrenia, although both the conditions lie in the domain of 'paranoid spectrum'. The present study was an attempt in this direction.
In this comparative study, the tests of neurocognitive functions chosen were based on the findings of earlier studies on patients with DD. These studies suggested that a wide range of cognitive functions are affected in DD, notably attention, memory, executive functions, and learning. 
The three study groups were matched on variables of age, sex, and level of education. Both patient groups were evenly matched on various clinical variables, including age of onset of illness, BPRS score, MADRS score, lag period for treatment, duration of treatment, and average dose of current antipsychotics in terms of chlorpromazine equivalence. There was no significant difference in the handedness in the study groups as well. Hence, it can be said that the difference seen between the patient groups cannot be ascribed to any of these variables. Neurocognitive testing shows that in general patients with DD performed relatively poorly than the normal controls and patients with paranoid schizophrenia performed somewhere in between the other groups. Compared with healthy controls, patients with DD performed poorly on various neurocognitive tests including assessment of IQ, and these differences between DD and the controls persisted even after controlling for intelligence quotient. Earlier studies that evaluated patients with DD reported abnormalities in cognitive flexibility, associative learning, and verbal and visuospatial skills that are mediated by frontal-subcortical systems and temporal areas. The results of the present study also suggest that patients with DD have impairment on a wide range of neurocognitive functions that depend on frontal and temporal lobes. ,
Patients with DD had insignificant poor performance on various neurocognitive tests, compared with patients with paranoid schizophrenia, except for some of the tests of attention and on WCST. This finding is similar to that reported by an earlier study, although in that study patients with schizophrenia performed poorly. These minor differences between the present study and the earlier study could be due to methodological differences particularly lack of matching in the earlier study. 
There are several possible explanations for more severe neurocognitive deficits in the DD group. Neurocognitive impairment could result from poor compliance to antipsychotics often seen in patients with DD,  as there is some suggestion that chronic neuroleptic administration may improve performance on tasks requiring sustained attention and visuomotor problem-solving abilities. 
Neurocognitive deficits are well known in patients with paranoid schizophrenia. In contrast to paranoid schizophrenia, neurocognitive deficits have received less attention in patients with DD. The possible reason for the same may be that although DD runs a chronic course, patients with disorders mostly have good functionality and usually do not stick to treatment; hence, they are less frequently assessed for their neurocognitive deficits. Findings of the present study suggest that neurocognitive deficits are quite prevalent and are more severe in patients with DD compared with those with paranoid schizophrenia. Considering that both the disorders lie in the same paranoid spectrum, it is quite possible that the same underlying biological factors may be responsible for neurocognitive deficits in both the disorders.
The present study is limited by small sample size. The sample was homogeneous in terms of age, basic level of education, and duration of illness, which may not reflect diverse clinical situations in real-life patients.
To conclude, the present study suggests that compared with the paranoid schizophrenia group, the persistent DD group showed significant impairment on the tests of focused attention and set shifting. Compared with normal controls, patients with persistent DD have significant impairment on the tests of focused attention, visual working memory, set shifting, visual learning and memory, and tests of IQ.
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[Table 1], [Table 2], [Table 3], [Table 4]