PARKINSON'S DISEASE

What Is Parkinson's Disease? Parkinson's disease (P.D.) is a degenerative disorder of the central nervous system which causes dysfunction of the motor system (i.e. the part of the nervous system responsible for muscle control and movement). The illness is manifest as tremor, rigid muscles, decreased voluntary movement and abnormal posture. The disease is most common among, but not exclusive to, men over 40. P.D. affects approximately 1 in 1000 people in the general population, and up to 1 in 100 people over 65.

What Causes Parkinson's Disease? The immediate cause of motor dysfunction is a deficiency of the neurotransmitter dopamine or a relative excess of acetylcholine in the brain. (In general, neurotransmitters are chemicals that carry signals between nerve cells.) In true P.D, the cells responsible for production of dopamine (cells in the substantia nigra, a specific region of the brain) are mysteriously destroyed; the illness is idiopathic, meaning that its cause is unknown. The role of genetic and environmental factors is uncertain. Some patients suffer from a similar symptom complex known as Parkinsonism, which results from a similar chemical imbalance but is not due to destruction of the substantia nigra. Parkinsonism may be caused by drugs (including anti-psychotic medications and MPTP, in illegal opiates), or by other distinct neurological illnesses which damage dopamine-producing cells.

What Are The Signs And Symptoms Of Parkinson's Disease? P.D. is often insidious in onset, beginning with weakness and/or tremor. Usually the disease progresses slowly over several years, but occasionally it follows a more aggressive course, leading rapidly to severe disability. The "pill-rolling" tremor typical of P.D. is seen in the hands at rest (as opposed to essential tremor, common in the elderly, which occurs during arm movement). Muscles become rigid, resulting in a stooped, stiff posture while standing, and a shuffling gait with loss of normal arm swing while walking. Speech may become slurred, monotonous, or inaudible; similarly, handwriting becomes small and cramped. The patient's face may appear mask-like, expressionless and still. In addition to these purely motor symptoms, patients with P.D. often suffer mental problems, including slowed thinking, insomnia, dementia and depression. They also experience various other physical problems including sexual difficulty, constipation, fatigue and excess sweating.

Psychiatric Disturbances In Parkinson's Disease: Up to 30% of patients with P.D. eventually develop dementia, an impairment of intellectual function involving memory loss, mood swings, altered social behaviour and impaired daily functioning. Unfortunately, response to treatment for dementia is poorer among patients with P.D. than among other patient groups. Many patients with P.D. also become clinically depressed; whether this is a psychiatric response to the physical illness or part of the same problem is unknown. Depression is treated with medications and psychotherapy, as in patients who do not have P.D.

How Is Parkinson's Disease Diagnosed? When the above mentioned symptoms are detected on physical exam and secondary causes of Parkinsonism can be ruled out, then the diagnosis of P.D. is made. Specifically, a physician will look for tremor, rigidity, akinesia (lack of voluntary movement), postural abnormalities, and brisk or decreased reflexes (e.g. the knee-jerk reflex). A mental status exam may be performed if P.D-related dementia is suspected, and a series of questions related to mood and motivation will determine the presence of depression.

What Is The Treatment Of Parkinson's Disease? Unfortunately, there is no known cure for P.D. The goals of therapy are to maintain or increase the amount of dopamine available to brain cells, thus enabling normal movements. In early stages of the disease, a class of drugs called MAO-B inhibitors can help to slow the degenerative process (the mechanism of action is unknown). Relief of mild symptoms such as tremor may be achieved with anti-cholinergic drugs, which act to correct the acetylcholine-dopamine imbalance characteristic of P.D. Side effects of these medications include dry mouth, blurred vision, constipation and confusion. Later in the course of illness, medical replacement of dopamine becomes necessary. The most effective drug regime includes 3 components: a chemical precursor of dopamine (e.g. levodopa or l-dopa), a second chemical to inhibit dopamine breakdown (e.g. carbidopa or benserazide), and third, a dopamine agonist (e.g. bromocriptine or pergolide) to mimic and prolong the action of dopamine or levodopa. Patient response to dopamine-based medical therapy is highly variable both in symptom relief and side effects, which include stomach upset, irregularities of heart beat (arrhythmias), involuntary movements and psychiatric disturbances. The effectiveness of medication may vary unpredictably over time; in some cases, this can make P.D. a difficult illness with which to cope.

New Treatment Possibilities: There is very active research going on in the field of P.D. Several surgical options have recently become available. Tremor and abnormal movements are eliminated quite successfully by creating a small lesion in the thalamus or the pallidum, two areas of the brain involved in the dopamine motor pathway. Stimulation of deep areas of the brain with electricity is currently under investigation as a possible treatment for P.D. Another area of research is the implantation of dopamine-producing cells (either fetal or genetically engineered) into the appropriate brain areas.