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Parkinson's disease (PD) is the most common movement disorder and is an adult-onset, neurodegenerative disease characterized by tremor at rest, rigidity, and bradykinesia.(1, 2) PD is a neurodegenerative condition, with the most characteristic pathologic feature being a loss of dopamine-containing neurons whose nuclei reside in the pars compacta of the substantia nigra and whose axons terminate in the caudate nucleus and putamen (the striatum).(3) Other pigmented and nonpigmented nuclei in the brainstem and elsewhere are affected as well. Associated with neuronal loss is the development of concentric hyalin inclusions in the cytoplasm of affected neurons called Lewy bodies. Symptoms are believed to be related to the imbalance between dopaminergic and cholinergic influences on striatal tissue created by the loss of dopamine-containing neurons, with proper striatal function depends on this balance.(4) Although parkinsonism may result from substance exposures, infection, and a host of other conditions, idiopathic disease remains the most common form.(5)
PD is an affliction of mid to late adult life, although 30 percent of patients report recognizable symptoms before the age of 50.(6) Another 40 percent develop the disease between ages 50 and 60, and the remainder greater than 60 years old at the time of diagnosis. The classic syndrome of parkinsonism includes tremor at rest, rigidity, bradykinesia, masked face, stooped posture, urinary dysfunction, and a shuffling gait.(7, 8) Although tremor is the most obvious initial finding, it is absent in a small percentage of patients.(9) PD may begin insidiously with vague, aching pain in the limbs, neck, or back and with decreased axial dexterity before tremor is noted. Dysarthria may be an early feature, although dysphagia usually occurs later.(10) Significant orthostatic symptoms may predominate in some patients, with other early subtle symptoms including a decrease in the caliber of handwriting and the volume of voice.(11) Depression is a significant component in many patients and may be a feature of the early disease as well.(12) The estimated frequency of dementia (which usually develops late) varies widely, but at least 15 to 20 percent of patients develop cognitive impairment.(13) However, dementia is not inevitable and remediable causes of mental status changes always need to be sought.
The classic presentation of PD usually poses few problems in diagnosis. There are several presentations that may be more problematic. These include isolated tremor at presentation, symptoms confined to half of the body (hemiparkinsonism), and the presence of these symptoms in younger patients. Symptomatic parkinsonism can be seen in several other disorders, such as progressive supranuclear palsy and multisystemic atrophy or as a side effect of numerous medications. An extrapyramidal syndrome that looks like that of parkinsonism also occurs in Alzheimer's disease and many other conditions.(14) The clinical diagnosis of PD is based on a careful examination in which the clinician looks for physical signs other than basal ganglia ones, elicits a careful drug and family history, and most likely does at least one neuro-imaging.(15)
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