ABSTRACT
Parkinson’s disease (PD) is associated with a combination of characteristic clinical signs and symptoms which, in established cases, should allow for prompt and accurate diagnosis. Diagnosis is obviously essential for patient management as well as for epidemiologic studies and clinical trials of new medications, most of which are much more effective in PD than in other parkinson syndromes. In the absence of reliable biological markers for the diagnosis of PD diagnosis must rest on clinical criteria. The classical three cardinal signs of PD are tremor, rigidity, and akinesia. It is generally accepted that the presence of at least two of these signs is required for the diagnosis of PD. Postural instability is often considered a fourth cardinal sign but is less useful for early diagnosis, as it typically appears only later in the course of PD and is such a common feature of other forms of parkinsonism. Despite these simple criteria, underdiagnosis and misdiagnosis remain common. Regarding underdiagnosis, in one door-to-door survey, 24 percent of cases were detected for the first time at the time of the survey.1 Underdiagnosis in the elderly occurs because bradykinesia and postural instability are common features of aging as well as chronic cerebrovascular disease. As a result, loss of facial expression, stooped posture, gait unsteadiness, and tremor are often attributed to aging by both laypersons and physicians. Misdiagnosis occurs because parkinsonism is a symptom complex as well as a disease and may be the result of a variety of underlying causes. The common use of qualifying terms such as parkinson syndrome, “atypical parkinsonism,” or “Parkinson plus” indicates the general awareness that other forms of parkinsonism exist. Autopsy studies have shown that the clinical diagnosis of PD is incorrect in as many as 20 to 25% of cases.2, 3 This indicates that, although symptoms and signs of parkinsonism may be correctly identified in life, the diagnosis of idiopathic PD is often incorrect. Idiopathic PD can be definitively diagnosed only by neuropathological examination with findings of neuronal loss in the substantia nigra and the presence of Lewy bodies in substantia nigra and other brain nuclei such as locus ceruleus, nucleus basalis of Meynert, dorsal motor nucleus of the vagus, and hypothalamus. The most common alternative causes of parkinsonism that are discovered at autopsy, all of which lack characteristic Lewy bodies, are multiple system atrophy
(MSA), progressive supranuclear palsy (PSP), Alzheimer’s disease, and diffuse cerebrovascular disease.3
