Parkinson’s disease (PD) is a chronic neurodegenerative disorder of unknown cause, which typically affects people in middle to late life. Named for Dr. James Parkinson, who first described the disease over 180 years ago, Parkinson’s disease needs to be distinguished from Parkinsonism, a descriptive term applied to various features of the disease. Parkinsonism applies to the syndrome of hand tremor, muscle stiffness, slowed body movements, and unsteady posture and gait. Parkinsonism can be caused by certain medications or illicit drugs, as a result of viral infection, secondary to a number of environmental exposures (insecticides, contaminated water supplies), or by Parkinson’s disease. A diagnosis of Parkinson’s disease implies that the Parkinsonism is of unknown cause, chronic and progressive in nature, and other prominent neurological dysfunctions are absent.
Parkinson’s disease is newly diagnosed in approximately 5,000 Americans each year. It is believed to affect 1 million Americans and 1-2 per 1,000 people will likely develop the disease. The incidence of Parkinson’s disease is expected to rise as the population continues to age. Two in 100 seniors over the age of 65 have the disease and perhaps up to 50% of those 85 and older meet criteria for the diagnosis. Disease onset is often between the ages of 55 and 65, and men are affected roughly 1.5 times as often as women. Less than 5% of all cases are in people under 40, with many such cases having a genetic link.
Nerve cells in the midbrain, which produce the neurotransmitters dopamine and norepinephrine, are known to degenerate in Parkinson’s disease, although the reason for this is unclear. The decrement in these neurotransmitters yields decreased stimulation of the brain’s motor cortex, and the resulting core symptoms of the disease.
Cardinal features of Parkinson’s disease can be recalled using the mnemonic “TRAP”—tremor, rigidity, akinesia, and postural abnormalities. Patients typically exhibit a hand tremor at rest, often more pronounced unilaterally. Rigidity or stiffness of the arms, legs, and/or neck is quite common. Akinesia, the absence of spontaneous motor movements, or bradykinesia, a slowing of the body’s overall motor activity, can be the most striking feature of the illness. Patients with Parkinson’s disease may appear statue-like with expressionless faces, in the extreme. They frequently have postural abnormalities as well, such as impaired balance and unsteady gait. The presence of two or more such signs or symptoms make the diagnosis quite likely.
A number of other symptoms are common, including constipation, urinary incontinence, sexual dysfunction, difficulty swallowing, weakened speech, sleep disorders, and visual disturbances. Psychiatric illness is common as well, with depression and dementia each seen in approximately 40% of patients and psychosis in up to 10%. Half of all patients may experience pain as a result of their disease. Muscle or joint pains from abnormal posturing, headaches, gastrointestinal discomfort, and sleep-related discomfort are fairly common.
Treatment includes both lifestyle modification and medications. Patient and family education is essential. Routine exercise, dietary advice, a review of optimal sleep hygiene, and referral for physical, speech, or occupational therapy as indicated are also vital. Pharmacological treatments are focused on decreasing symptoms, enhancing mobility, slowing the progression of illness, and minimizing frequently encountered side effects. Commonly used medications aim to enhance the amount of dopamine receptor stimulation in the brain. This can be accomplished by (a) direct dopamine replacement (carbidopa/levodopa), (b) synthetic dopamine agents (bromocriptine, pergolide, ropinarole, and others), and (c) blocking the clearance of available dopamine (amantadine).
Potential side effects from such treatments include motor tics, delusional thinking, hallucinations (commonly visual), anxiety, restlessness and agitation, nausea, confusion, sedation, decreased blood pressure with an increased risk of falls, and other cardiac side effects. In treatment-refractory cases, neurosurgical procedures may be considered. Options include resection, or more recently, implantable electrode stimulation of different deep brain regions collectively known as the basal ganglia. A partial response or better is reported in up to 90% of patients with such procedures. However, potential complications include infection, hemorrhage, or stroke.
Limited evidence exists to support the role of medicines such as selegiline or vitamin E in prevention of Parkinson’s disease. Estrogen replacement, which is known to modulate neurotransmission, may have an undefined role in preventing Parkinson’s disease.