Parkinson's Disease Health Article

Definition

Parkinson's disease (PD) is a motor system disorder caused by the chronic, progressive degeneration of neurons (nerve cells) in regions of the brain that control movement. PD causes a decline in the initiation, speed, and smoothness of movement. Over time it may come to affect many bodily functions.

Description

Parkinson's Disease (PD) was first described in 1817 by James Parkinson. It affects more than one million people in the United States, including some 500,000 people who have yet to be diagnosed. About 50,000 new cases are diagnosed each year. The average age of PD onset is 60. Symptoms of PD are seen in as many as 15% of those between the ages 65 and 74 and almost 30% of those between the ages of 75 and 84. Only 5 to 10% of PD cases occur before the age of 50. Young-onset PD occurs in those under age 40. A parent or sibling with PD increases one's risk of developing the disease.

PD results from the degeneration and death of neurons in the substantia nigra, movement control centers on each side of the brain. These cells secrete dopamine, a neurotransmitter that attaches to receptors on cell surfaces in another part of the brain—the corpus striatum—that controls muscle action. When dopamine levels fall, the neurons of the corpus striatum begin to misfire. It is estimated that dopamine-producing cells begin dying about 13 years before PD symptoms become evident. The symptoms of PD begin when about 60% of the dopamine-producing cells have died.

Causes

Although the cause of Parkinson's Disease (PD) is unknown, it appears to result from a combination of environmental and hereditary factors as well as oxidative damage and aging. Factors for PD may include:

• herbicide and pesticide exposure
• an as-yet-unidentified toxin or virus
• cellular damage from oxidation by free-radicals (atoms or molecules with an unpaired electron)
• loss of dopamine-secreting cells with age, particularly with accelerated aging
• fewer dopamine-secreting cells at birth

Symptoms

Early symptoms of PD often are quite subtle, developing on one or both sides of the body. The primary symptoms of PD are:

• tremors (shaking) while at rest. (The classic PD tremor is the rubbing of the thumb and forefinger at a frequency of about three rubs per second. Tremors may spread to the hands, arms, legs, feet, jaw, and face. The tremors increase with stress. However, many people with PD do not experience tremors)

• slow movement (bradykinesia) or freezing during movement (akinesia)
• stiffness or rigidity of the limbs and trunk
• poor balance leading to frequent falls

Other early symptoms of PD:

• short, shuffling steps
• stooped posture
• masking (reduction) of facial expression and infrequent blinking
• slow or rapid, soft, monotonic (without inflection) speech
• other speech changes
• insomnia, restlessness, and nightmares
• depression
• emotional changes, including fear, irritability, and insecurity
• incontinence
• constipation
• small, illegible handwriting
• frequent, dramatic swings in mobility and moods

Later-stage PD symptoms may include:

• frozen muscles that prevent the initiation of movement
• oily or very dry skin
• sweating
• digestive tract shutdown causing difficulties in swallowing, digesting, and elimination
• auditory and/or visual hallucinations
• progressive deterioration of intellectual function
• (dementia), affecting 30 to 40% of those with late-stage PD
• loss of contact with reality (psychosis)

Medications for PD can also cause some of these symptoms.

Diagnosis

There is no definitive test for PD. Diagnosis is based on a careful medical history and complete neurological examination.

In addition to PD, anything that damages the substantia nigra can cause Parkinson's-like symptoms, called parkinsonism. Possible causes of parkinsonism:

• infection
• nausea
• trauma
• stroke
• exposure to manganese or other toxins
• medications for psychiatric disorders, such as haloperidol (Haldol) or chlorpromazine (thorazine)
• a chemical called MPTP, found as an impurity in some illegal drugs
• epilepsy
• alzheimer's disease
• other neurodegenerative diseases that sometimes are referred to as Parkinson's plus or parkinsonism plus syndromes

Brain scans, blood tests, lumbar puncture, or x rays may be used to rule out causes of parkinsonism other than PD.