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Parkinson disease (PD) is a highly prevalent neurodegenerative disorder secondary in prevalence only to Alzheimer disease.1 Approximately 2% of the geriatric population is affected, though younger persons can also develop the disease.2 The mean age of onset is 65 years, and men are affected more often than women. Associated morbidity is substantial, and results in increased hospitalizations, increased prescription drug utilization and more frequent placement in long-term care facilities as compared to the general population.3 Though in most cases persons with PD can expect to live into old age, their life expectancy is somewhat shorter than average.4,5 The disease is progressive, and no cure has been identified to date.

The underlying mechanism of PD development is not well understood, but genetic predisposition, environmental toxins, and the sequelae of infection have all been implicated.6 Loss of nigrostriatal neurons in the substantia nigra pars compacta and Lewy body formation (misfolded proteins) are the pathological hallmarks of the disease. By the time symptoms emerge and a diagnosis is made, it is estimated that 80% of nigrostriatal neurons have been lost.7 Due to a resultant deficiency in the neurotransmitter dopamine, there is less inhibitory output from the basal ganglia.8 The neurotransmitter imbalance allows for relative overactivity of acetylcholine, and is responsible for the abnormalities of motor function that characterize the disease. The cardinal features of PD include tremor, bradykinesia, rigidity, and postural instability (though this symptom is rare in the early stages of the disease). PD symptoms typically begin unilaterally in the extremities, and spread to the opposite side as the disease progresses. Presentation varies among individuals and can differ substantially from person to person.

Tremor is the most common PD symptom, however not all patients have one.9 Some may complain of feeling an internal vibration that is not outwardly apparent. In mild disease, the tremor (often described by the term "pill rolling" as the fingers and thumb move in opposite directions), disappears with purposeful movement and during sleep. In some cases tremor may also be present in the lips, chin, and jaw.

Bradykinesia, or slow movement, may result in difficulty with tasks requiring repetitive movements and fine motor control (such as teeth brushing). Arm-swing when walking may be diminished or absent, and spontaneous gesturing and facial expression are often blunted. A shuffling gait may become apparent, and difficulty turning in bed or rising from a chair may affect the PD patient's ability to function. Handwriting frequently becomes smaller (micrographia) and difficult to read. Bradykinesia is the symptom that most PD patients consider most distressing. Eventually, all voluntary movements will be affected to some degree.

Rigidity is more common in older patients upon initial presentation.6 This symptom will be observed as resistance in the muscles upon initiation of passive movement. The rigidity of PD is often described as "jerky" or "cogwheeling" in nature.10 Vague muscle ...

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