THE EFFECT OF DIFFERENT DIAGNOSTIC-CRITERIA ON THE PREVALENCE OF DEMENTIA

Background There are several widely used sets of criteria for the diag nosis of dementia, but little is known about their degree of agreement and their effects on estimates of the prevalence of dementia. Methods We examined 1879 men and women 65 years of age or older who were enro lled in the Canadian Study of Health and Aging and calculated the prop ortion given a diagnosis of dementia according to six commonly used cl assification systems: the American Psychiatric Association's Diagnosti c and Statistical Manual of Mental Disorders (DSM), third edition (DSM -III), the third edition, revised, of the DSM (DSM-III-R), the fourth edition of the DSM (DSM-IV), the World Health Organization's Internati onal Classification of Diseases (ICD), 9th revision (ICD-9) and 10th r evision (ICD-10), and the Cambridge Examination for Mental Disorders o f the Elderly (CAMDEX). The degree of concordance among classification schemes and the importance of various factors in determining diagnost ic agreement or disagreement were examined. Results The proportion of subjects with dementia varied from 3.1 percent when we used the criter ia of the ICD-10 to 29.1 percent when the DSM-III criteria were used. The six classification systems identified different groups of subjects as having dementia; only 20 subjects were given a diagnosis of dement ia according to all six systems. The classifications based on the vari ous systems differed little according to the patients' age, sex, educa tional level, or status with respect to institutionalization. The fact ors that most often caused disagreement in diagnosis between DSM-III a nd ICD-10 were long-term memory, executive function, social activities , and duration of symptoms. Conclusions The commonly used criteria for diagnosis can differ by a factor of 10 in the number of subjects clas sified as having dementia. Such disagreement has serious implications for research and treatment, as well as for the right of many older per sons to drive, make a will, and handle financial affairs. (C) 1997, Ma ssachusetts Medical Society.