STANDARDIZATION OF THE DIAGNOSIS OF DEMENTIA IN THE CANADIAN STUDY OFHEALTH AND AGING

Standardization of diagnostic procedures for cognitive impairment in l arge epidemiologic surveys remains difficult. This paper reports resul ts of diagnostic standardization in a subsample of 2,914 elderly (age 65 years +) Canadians from the Canadian Study of Health and Aging (CSH A; n = 10,263). The objectives were to measure the consistency of the CSHA diagnosis as a test of validity; to assess inter-rater reliabilit y, and to assess the impact of neuropsychological data on the diagnosi s of dementia. The CSHA clinical assessment included a nurse's examina tion, Modified Mini-Mental Status (3MS) exam and Cambridge Mental Diso rders Examination, neuropsychological tests, medical history and exami nation, and laboratory investigations. A final diagnosis was reached i n a consensus conference which incorporated preliminary diagnoses from both physicians and neuropsychologists. Computer algorithms, which we re developed to check consistency between the clinical observations an d the final diagnosis, demonstrated 98% concordance with DSM-III-R cri teria for dementia and 92% with NINCDS-ADRDA (National Institute of Ne urological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association) criteria for probable Alzhe imer's disease. Inter-rater agreement was high: kappa = 0.81 for demen tia/no dementia; kappa = 0.74 for normal/cognitive impairment, not dem entia/dementia. Comparisons of diagnoses between raters by clinical sp ecialty revealed few systematic differences. The impact of neuropsycho logical input on the physician's diagnosis was most marked in the bord erline cases between diagnostic categories.