Parkinson’s disease, or parkinsonism, is a syndrome (i.e., a constellation of clinical signs and symptoms) consisting of four cardinal features: resting tremor, bradykinesia (physical and mental sluggishness), rigidity, and impaired postural reflexes. The diagnosis is made on the basis of finding any three of the four cardinal features.

Distribution and Incidence

This disease occurs throughout the world, with no population protected against the condition. Most surveys have investigated Caucasian populations of northern European or of Anglo-Saxon descent, and few studies have been done on the occurrence of Parkinson’s disease in other populations. In Caucasians the prevalence is 84 to 187 per 100,000 of population, with no geographic patterns and no clusters of increased incidence. Two studies seem to indicate a lower prevalence in blacks; this has been the clinical experience as well, probably indicating a decreased risk of Parkinson’s disease for blacks. The annual incidence varies from 5 to 24 per 100,000 of the white population. These figures, of course, depend on the methods of ascertainment, the population studied, the length of time that data have been collected, and many other factors. If the prevalence is divided by the annual incidence, the average duration of the illness is approximately 10 years.

Epidemiology

Parkinson’s disease usually occurs in late middle life or beyond. The mean age of onset is 58 to 62. Onset before age 30 is rare but is not unknown, and there is a juvenile form of Parkinson’s disease. The greatest incidence is in the decade age 70 to 79 years, with an incidence of 1 to 2 per 1,000 population per year.