What is Parkinson's disease and who gets it?

The exact number of people in South Africa with the illness is unknown, but the prevalence is about 325 per 100,000. As said above it is a degenerative disease, meaning that it gets worse with time.

The four main features of Parkinson's are

1. resting tremor
2. slowness of movement, also called bradykinesia
3. abnormal posture, often flexed, stooped over and with abnormal balance
4. muscle rigidity, classically described as cogwheel where the joint responds with a series of ratchet-like catches and increased resistance on movement

Other features are progressively smaller writing and a rigidity of the facial muscles causing a rather blank expression.

An elderly person with 2 or more of these symptoms is generally said to have Parkinson's disease. Other diagnoses such as Alzheimer's, multiple system atrophy and certain drugs and toxins can give the same picture. In these cases this is described as Parkinsonism and is distinguished from true or idiopathic Parkinson's.

The disease often starts on one side of the body and gradually spreads until it affects all limbs. To begin with patients may have only the tremor at rest, but as the years progress they find that they have difficulty turning over in bed or getting out of the bath.

Some patients also develop dementia and slowness of thought (bradyphenia). Something like 30% of Parkinson's patients become demented compared with 10% of the rest of the population. Depression is often a feature of the illness. It is also possible for an elderly person to have both Parkinson's and Alzheimer's.

What causes Parkinson's?

We are not sure exactly what causes Parkinson's disease, although we do know that in those with the disease, the cells in the part of the brain which produce dopamine, a neurotransmitter, called the subtantia nigra, degenerate. With this the amount of dopamine produced is progressively reduced. The dopamine is important in controlling movement which is mediated via the subtantia nigra to the basal ganglia of the brain. Normal function of the basal ganglia seems to depend on the balance of input from dopamine and other neurotransmitters. With the loss of dopamine, it's inhibitory affect on another part of the brain, the globus pallidus is reduced, and so there are now bursts of activity in the basal ganglia which feed back to the motor cortex, the overall movement control centre in the brain. It is this combination of events which leads to the characteristic movement disturbance of Parkinson's.

While there is no definite pattern of inheritance it does seem that there is an inherited component which involves the metabolic potential to handle toxins, specifically environmental toxins which target the dopamine producing cells in the brain.

How is Parkinson's treated?

The mainstay of treatment of Parkinson's is levodopa (Larodopa®) which replenishes the levels of dopamine in the brain. It is usually combined with either carbidopa (Sinemet®) or benserazide (Madopar®), substances which increase the amount of levodopa available in the brain. Levodopa is generally regarded as the most effective drug in the treatment of Parkinson's, but, because the efficacy starts to decrease after about 5 years, therapy should be delayed as long as possible. At the beginning of the disease patients may get as much as 7 or 8 hours of benefit from levodopa, but after 4 to 5 years this is reduced to 3 or 4 hours. Long term therapy with levodopa has side effects which include abnormal movements and fluctuations in ability to move, this latter known as the 'on-off' phenomenon. In this there is normal mobility in the 'on' phase, contrasted with almost total rigidity in the 'off' phase.

A strategy to counteract the potential side effects of levodopa is to give it in combination with other drugs. Selegiline (Eldepryl®) can help control the 'on-off' effect and if started in the early stages of the disease can delay the need for levodopa by 12 to 18 months. Other drugs used include the dopamine receptor agonists, which block the uptake of dopamine in the brain and so increase its availability. These are bromocriptine (Parlodel®) and pergolide (Permax®).

A new class of drugs has recently been introduced into Parkinson's treatment. These are the so-called COMT (cathecol-O-methyl transferase) inhibitors. In combination with selegiline, they inhibit the breakdown of levedopa even further and increase levels of dopamine still further.

Less frequently used drugs are the anticholinergic agents such as Artane® (trihexyphenidyl) and Akineton® (biperiden). These are often used for drug induced Parkinson's rather than idiopathic Parkinson's.

Where do we go from here?

Surgery for Parkinson's is the newest, and so least tested, option for therapy. In the view of a leading South African expert on Parkinson's disease, Professor Temlett of the University of the Witwatersrand Medical School, it should not be carried out within the first few years of the disease. Since it is important to make sure that the correct diagnosis has been made, a good response to anti-Parkinson's drugs should have been seen first. In most cases surgery is reserved for patients who have been on levedopa for 5 to 10 years and have shown a response, but who now have either developed complications of the drug, or are no longer responding.

Pallidotomy is the most commonly used surgical procedure in Parkison's disease. (See Parkinson's in the Questions section). In this the globus pallidus, overactive due to loss of dopamine, is destroyed. In South Africa about 200 pallidotomies have been performed. 7 out of every 10 patients report that they have improved as a result of the surgery. The remaining patients have not improved, but are no worse.

Thalamotomy is an old procedure and works mainly for alleviation of the tremor.

Dopamine cell transplantation is one of the newest possible treatments, but has ethical problems because it involves using foetuses. It is only in the experimental stages as yet.

The latest surgical technique involves the use of a 'pacemker' which interrupts the neuronal traffic in the basal ganglia. This is apparently successful, but at R70 to R80,000 per procedure its use will be very limited.

There are many links to Parkinsons's sites in Hotlinks on the Doctor Online site. For further information on Parkinson's support groups contact the South African Parkinsonian Association, Private Bag X36, Bryanston, 2021, tel/fax: (011) 787 8792.