Mortality from Parkinson's disease in England and Wales 1921-89.

Mortality from Parkinson's disease in England and Wales was re-examined using published government statistics. The 300% increase in the crude mortality rate between 1921 and 1989 was largely attributable to the increase in the elderly population who suffer a higher prevalence of the disease. The dramatic fall in 1940 and rise in 1984 were artefacts caused by changes in certification. Age-specific mortality fell after 1940 in all groups below 70 years and in both sexes, but increased in those over 75 years. Analysis by birth cohort showed a progressive decline in mortality at younger ages with successive cohorts but stable mortality in the elderly. Younger patients were probably misclassified cases of "late-onset" Parkinsonism following encephalitis lethargica who can be differentiated from older cases of idiopathic Parkinson's disease. Mortality decreased in all age groups in the 1970s but then increased in the early 1980s. This is comparable to trends in the United States and Scandinavia and suggests that the beneficial effects of levodopa delay death for several years.