The natural history of the disease is of interest. As a rule, it begins between 45 and 70 years of age, with the peak age of onset in the sixth decade. It is infrequent before 30 years of age, and most series contain a somewhat larger proportion of men. Trauma, emotional upset, overwork, exposure to cold, “rigid personality,” and so on, were among many factors that had been suggested over the years as predisposing to the disease but there is no evidence to support any such claims. Idiopathic Parkinson disease is observed in all countries, all ethnic groups, and all socioeconomic classes, although the incidence in African Americans is lower than in whites. There may be an increased incidence in rural compared to urban areas, attributed tentatively and not consistently, to exposure to pesticides. In Asians, the incidence is one-third to one-half that in whites. The disease is frequent in North America, where there are approximately 1 million affected patients, constituting about 1 percent of the population over the age of 65 years. The incidence in European countries where vital statistics are kept, is similar. A possible relationship to repeated cerebral trauma and to the “punch-drunk” syndrome (dementia pugilistica; chronic traumatic encephalopathy) has been particularly problematic and is unresolved despite several celebrated cases (Lees); certainly most cases do not have this exposure. A protective effect of smoking and coffee drinking has emerged in some epidemiologic studies but the magnitude of effect is marginal.
A tetrad of hypoand bradykinesia, resting tremor, postural instability, and rigidity are the core features of
Parkinson disease. These are evident as an expressionless face, poverty and slowness of voluntary movement, “resting” tremor, stooped posture, axial instability, rigidity, and festinating gait. Much can still be gained from perusal of the often-cited study by Hoehn and Yahr, published in 1967 before the widespread use of l-dopa. Table 38-2 is reproduced from that paper although more extensive grading scales such as the Unified Parkinson Disease Rating Scale (UPDRS) are in frequent use. Because of the common use of the latter instrument in clinical trials, it is appropriate for the clinician to be familiar with its broad outlines. This complex scale encompasses subsections on motor and mental function and activities of daily living, and gives a summed score ranging from 0 to 176 with higher numbers denoting more severe disease manifestations.
One of the most interesting clinical aspects of the disease is the lack of concordance across symptoms—a tremor predominant form with few other symptoms is well known and even hypokinesia (a lack of shifting of natural postures and a tendency to stay still) and bradykinesia (slowness of commended or intended movement) in some cases seem to be somewhat dissociated. The manifestations of basal ganglionic disease are fully described in Chap. 4, and only certain diagnostic problems and variations of the clinical picture need be considered here.