Parkinson's Disease

Parkinson's disease (PD) is a degenerative disorder of the central nervous system. It was first described in 1817 by a British physician named James Parkinson. In the United States, at least 500,000 people are believed to suffer from Parkinson's disease, and about 50,000 new cases are reported annually.

Symptoms and Diagnosis

Parkinson's disease belongs to a group of conditions called movement disorders. The four main symptoms are

• Tremor. Typically, the tremor takes the form of a rhythmic back-and-forth motion at a rate of 4-6 beats per second. It may involve the thumb and forefinger and appear as a "pill rolling" tremor. Tremor often begins in a hand, although sometimes a foot or the jaw is affected first. It is most obvious when the hand is at rest or when a person is under stress..
• Rigidity. A major principle of body movement is that all muscles have an opposing muscle. Movement is possible not just because one muscle becomes more active, but because the opposing muscle relaxes. In PD, rigidity comes about when, in response to signals from the brain, the delicate balance of opposing muscles is disturbed. The muscles remain constantly tensed and contracted so that the person aches or feels stiff or weak. The rigidity becomes obvious when another person tries to move the patient's arm, which will move only in ratchet-like or short, jerky movements known as "cogwheel" rigidity.
• Bradykinesia. The slowing down and loss of spontaneous and automatic movement. Bradykinesia is particularly frustrating because it may make simple tasks somewhat difficult. The person cannot rapidly perform routine movements. Activities once performed quickly and easily - such as washing or dressing - may take several hours.
• Postural instability. An impaired balance. It causes patients to fall easily. Affected people also may develop a stooped posture in which the head is bowed and the shoulders are drooped.

These symptoms usually begin gradually and worsen with time. As they become more pronounced, patients may have difficulty walking, talking, or completing other simple tasks. Not everyone with one or more of these symptoms has PD, as the symptoms sometimes appear in other diseases as well.

There are currently no blood or laboratory tests that have been proven to help in diagnosing sporadic PD. Therefore the diagnosis is based on medical history and a neurological examination. Doctors may sometimes request brain scans in order to rule out other diseases.

Causes

Parkinson's disease occurs when nerve cells, or neurons, in an area of the brain known as the substantia nigra die or become impaired. Normally, these neurons produce an important brain chemical known as dopamine. Dopamine is a chemical messenger responsible for transmitting signals between the substantia nigra and the next "relay station" of the brain, the corpus striatum, to produce smooth, purposeful movement. Loss of dopamine results in abnormal nerve firing patterns within the brain that cause impaired movement. Studies have shown that most Parkinson's patients have lost 60 to 80 percent or more of the dopamine-producing cells in the substantia nigra by the time symptoms appear.

Many brain cells of people with PD contain Lewy bodies - unusual deposits or clumps of the protein alpha-synuclein, along with other proteins. Alpha-synuclein plays the central role in the development of Parkinson's disease and other diseases involving Lewy bodies (more info).

Scientists have identified several genetic mutations associated with PD (more info). Studying the genes responsible for inherited cases of PD can help researchers understand both inherited and sporadic cases. The same genes and proteins that are altered in inherited cases may also be altered in sporadic cases by environmental toxins or other factors. Researchers also hope that discovering genes will help identify new ways of treating PD.

Reference:

National Institute of Neurological Disorders and Stroke, USA.