A progressive brain disorder causing shaking and problems with movement
Parkinson’s disease results from degeneration of cells in a part of the brain called the substantia nigra. These cells project into the basal ganglia, which controls the smoothness of muscle movements. Normally, the cells in the substantia nigra produce a neurotransmitter (a chemical that transmits nerve impulses) called dopamine, which acts with acetylcholine, another neurotransmitter, to fine-tune muscle control. In Parkinson’s disease, the level of dopamine relative to acetylcholine is reduced, with the result that control of the muscles is impaired.
About 1 in 500 people in the UK has Parkinson’s disease. The disorder tends to occur after the age of 60 and is more common in men. Although the cause is not known, Parkinson’s disease occasionally runs in families and genetic factors may be involved in some cases.
Parkinsonism is the term used for symptoms of Parkinson’s disease when they are due to an underlying disorder (such as multiple strokes) or certain drugs. Repeated head injuries may cause parkinsonism, as may some antipsychotic drugs used to treat severe psychiatric illness.
The main symptoms of Parkinson’s disease develop gradually over months or even years. Parkinsonism may have a gradual or sudden onset depending on the cause. Symptoms include:
Tremor of one hand, arm, or leg, usually when resting, that later occurs on both sides.
Muscle stiffness, making it difficult to start moving.
Slowness of movement.
Shuffling walk with loss of arm swing.
Expressionless or mask-like face.
As the disease progresses, stiffness, im-mobility, and constant trembling of the hands may make some daily tasks difficult to perform. Speech may become slow and hesitant, and swallowing may be difficult. Many people with the disorder develop depression. An estimated 30 per cent of people with Parkinson’s disease eventually develop dementia but the dementia tends to develop in older people and is not thought to be solely due to the Parkinson’s disease.
Since Parkinson’s disease begins gradually, it is often not possible to diagnose the condition at first. Your doctor will examine you and arrange tests such as CT scanning or MRI to exclude other possible causes. If a specific underlying disorder is found, you will be diagnosed as having parkinsonism rather than Parkinson’s disease.
There is no specific cure for Parkinson’s disease, but drugs, physical treatments, and, more rarely, surgery can relieve symptoms. If you have parkinsonism due to medications, your doctor may change your drugs. Symptoms then usually disappear within 8 weeks. If the symptoms persist, you may need to be treated with anti-parkinsonism drugs.
In the early stages of Parkinson’s disease when symptoms are mild, treatment may not be necessary because drugs cannot change the progression of the disease. Later on, drugs are used to relieve symptoms and reduce disability by correcting chemical imbalances in the brain, either by boosting dopamine levels or by blocking some of the effects of acetylcholine or a combination of both.
An anticholinergic drug such as trihexyphenidyl (benhexol) is often given initially to reduce shaking and stiffness. Anticholinergic drugs can be effective for several years but they may cause side effects such as dry mouth, blurred vision, and difficulty in passing urine. They may also cause confusion and are therefore rarely used for elderly people.
The main treatments for Parkinson’s disease are dopamine agonists and levodopa. Dopamine agonists, such as ropinirole, pramipexole, and rotigotine, mimic the action of dopamine in the brain and help to control the main symptoms of the disease, such as tremor and mobility problems. Levodopa is converted into dopamine in the body and thereby increases dopamine levels in the brain. It is given in combination with an enzyme inhibitor (such as benserazide in the preparation co-beneldopa, or carbidopa in co-careldopa) to increase the amount of dopamine reaching the brain.
Levodopa preparations are generally more effective than dopamine agonists at controlling symptoms. However, they tend to work less well over time and the dose needs to be gradually increased. In addition, after several years of treatment (typically 5–7 years), levodopa preparations often produce side effects such as involuntary movements and an “on–off” effect (in which you suddenly switch from being able to move to being immobile). Consequently, most people are prescribed dopamine agonists first, and levodopa preparations are added later as the disease progresses.
Although many drugs are available for treating Parkinson’s disease, none reverses its progress. However, drug treatment may give sustained relief of the major symptoms.
The doctor may arrange for physiotherapy to help with mobility problems or speech therapy for speech and swallowing problems. If you are finding it difficult to cope at home, an occupational therapist may be able to suggest practical changes to help you move around.
People who are otherwise in good health may have surgery if the symptoms cannot be controlled by drugs. Surgery involves destroying a part of the brain tissue responsible for the tremor. Therapies still being assessed include replacement of damaged brain cells with transplanted tissue and deep brain stimulation with electrical impulses.
It is important to pay attention to your general health. Taking a walk each day and doing simple exercises will help you to maintain mobility. Emotional and practical help from family, friends, and support groups is also important. Many hospitals have a specialist Parkinson’s disease nurse, who can provide information and support.
The course of the Parkinson’s disease is variable, but drugs can be effective in treating the symptoms and improving the quality of life. People can lead active lives for many years after being diagnosed. However, most people with the disorder need daily help eventually, and their symptoms may be increasingly hard to control with drugs.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.