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Dementia occurring in patients with schizophrenia is not of Alzheimer’s type
- Sudhir Kumar, Soumitra S. Datta (Consultant Psychiatrist), Christian Medical College, Vellore (9 September 2003)
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Sudhir Kumar, Consultant Neurologist, Department of Neurological Sciences Christian Medical College Hospital, Vellore, India-632004, Soumitra S. Datta (Consultant Psychiatrist), Christian Medical College, Vellore
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sk{at}cmcvellore.ac.in Sudhir Kumar, et al.
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Sir, We read with great interest the recent article by Brodaty et al (2003). They report a high incidence of dementia in a long-term follow up of cognitively normal patients with schizophrenia. Though the study design and results are interesting, we would like to make certain comments. Firstly, there are many limitations in this study some of which authors have pointed out. 1) The sample size is small (19 and 24 patients in schizophrenia and control groups respectively) and only 70% follow up. 2) Unfortunately, only seven patients (out of a total of 27 at baseline) in the schizophrenia group have been interviewed. The data in remaining “followed up” patients have been obtained from informants. While informant reports are useful in making a diagnosis of dementia, 40% of such reports were found to be inaccurate in a study from the same centre (Kemp et al, 2002). However, some interview-based techniques such as Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE), Blessed-Roth Dementia Rating Scale (BDRS) and Clinical Dementia Rating (CDR) may be useful in making a diagnosis (Petersen et al, 2001). It would have been useful if more data were provided regarding the technique used in this study (including its specificity and sensitivity for making a correct diagnosis of dementia and its severity). 3) Six out of seven patients with schizophrenia had symptoms of psychosis at 5-year follow up. Psychosis is commonly associated with cognitive dysfunction and it would have interesting to see whether presence of psychosis could partly explain the cognitive impairment. 4) Patients in schizophrenia group had significantly fewer years of education and were significantly more likely to have never been married. Lack of education and illiteracy are associated with a higher incidence of Alzheimer’s disease and vascular dementia (Bowirrat et al, 2002; Lindsay et al, 2002). An excess risk of Alzheimer’s disease has been observed among never-married individuals as compared to those who were married or cohabitants (Helmer et al, 1999). Could the difference observed in this study be partly explained by these two factors? Despite these minor limitations, this study has highlighted that dementia occurs commonly in older patients with schizophrenia. The details of neuropsychological deficits in patients, however, have not been mentioned. Moreover, the study has failed in explaining the pathophysiological or morphological basis for dementia due to lack of neuroimaging and autopsy data. Though the predominant dementia was of Alzheimer’s type in this study (diagnosis based on interviews), the autopsy studies show evidence against this. In an autopsy series of 99 cases with schizophrenia, dementia of Alzheimer’s type was seen in only 7 cases (7.1%) (Jellinger et al, 1999). Similarly, in another study, only one patient met neuropathological criteria for AD out of 51 patients with schizophrenia (Murphy et al, 1998). This suggests that the frequency of AD in elderly schizophrenics is equal or even less than in the general population. However, the basis of cognitive impairment in schizophrenia is currently unknown (Harrison PJ, 1999). In conclusion, this study further corroborates the evidence that dementia is common in patients with late-onset schizophrenia. However, further studies are required to explain the exact type of dementia and its neuropathological basis. References Bowirrat A, Friedland RP, Farrer L, Baldwin C, Korczyn A. (2002) Genetic and environmental risk factors for Alzheimer's disease in Israeli Arabs. J Mol Neurosci, 19: 239-45. Harrison PJ. (1999) The neuropathology of schizophrenia. A critical review of the data and their interpretation. Brain, 122, 593-624. Helmer C, Damon D, Letenneur L, et al. (1999) Marital status and risk of Alzheimer’s disease: a French population-based cohort study. Neurology, 53, 1953-8. Jellinger KA, Gabriel E. (1999) No increased incidence of Alzheimer's disease in elderly schizophrenics. Acta Neuropathol (Berl), 97: 165-9. Kemp NM, Brodaty H, Pond D, Luscombe G. (2002) Diagnosing dementia in primary care: the accuracy of informant reports. Alzheimer Dis Assoc Disord, 16, 171-6. Lindsay J, Laurin D, Verreault R, et al. (2002) Risk factors for Alzheimer's disease: a prospective analysis from the Canadian Study of Health and Aging. Am J Epidemiol, 156: 445-53. Murphy GM Jr, Lim KO, Wieneke M, et al. (1998) No neuropathologic evidence for an increased frequency of Alzheimer's disease among elderly schizophrenics. Biol Psychiatry, 43: 205-9. Petersen RC, Stevens JC, Ganguli M, Tangalos EG, Cummings JL, DeKosky ST. (2001) Practice parameter: early detection of dementia: mild cognitive impairment (an evidence-based review). Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology, 56, 1133-42. |
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