THE NATURAL-HISTORY OF MENTAL DISORDER IN OLD-AGE - ALZHEIMERS-DISEASE AND DEPRESSIVE-ILLNESS COMPARED

Background. Depressive illness (DI) and Alzheimer's disease (AD) are i mportant causes of morbidity in old age and the relationships between these two disorders are uncertain. Method. In a prospective, descripti ve, comparative study of consecutive referrals aged over 65 years to o ne consultant, 218 patients with AD and 280 patients with DI were foll owed up for 15 years. Results. The prognosis of DI uncomplicated by ph ysical illness at referral was reasonably good and 5-year survival was double that of AD. The rate of occurrence of AD in DI is no greater t han in the general population. The higher mortality from cancer in DI than in AD is unexplained but may relate to differences in aetiology o f these two disorders. Conclusion. Although their symptoms frequently overlap, AD and DI are distinct disorders with very different prognose s and accurate diagnosis may have important implications for appropria te treatment. (C) 1998 John Wiley & Sons, Ltd.