Parkinson's disease (PD) is found worldwide and in every ethnic group where studies have been conducted. Celebrity sufferers - such as the boxer Muhammad Ali - and the highly visible nature of the symptoms have raised awareness of the condition in many countries. Memory impairment and a decline in general cognitive function occur in many patients with PD. Indeed some patients are diagnosed as suffering from coexisting Alzheimer's disease.
The condition was first identified by Dr James Parkinson in 1817. At the time it was termed "the shaking palsy". Parkinson's description of the disease refers to its most highly visible element - the tremor. This occurs when the patient is at rest and is typified by involuntary movement of the arms and legs. The tremor becomes gradually worse as the patient deteriorates.
Two other symptoms are commonly held to define PD - rigidity and slow movements. The rigidity results in dramatic loss of flexibility. The slow movement is characterized by the shuffling walk often associated with PD sufferers, as well as other loss of motor control and dexterity.
The cause of Parkinson's disease remains unknown. It is known that in PD there is a shortage in the production of the neurotransmitter dopamine. Other neurotransmitters such as acetylcholine, noradrenaline and serotonin are also affected in some patients with PD. At present there is no cure for PD. The main stay of treatment is to try and replace the depleted dopamine levels by administering L-dopa or giving drugs that prevent the breakdown of L-dopa (COMT inhibitors). The exact cause of the failure to maintain the dopamine balance is unknown. However, a number of factors - including heredity, head injuries and exposure to certain toxins - have been mooted.
The progress of the disease has been characterized of featuring an "on/off" process, periods where therapy and medication prove ineffective against the disease. There is growing interest in the use of the 'anti- alzheimer' drugs (acetylcholinesterase inhibitors) and antidepressants such as the selective serotonin re-uptake inhibitors as patients may have coexisting memory failure and depression.
Some advances in surgical procedure such as the transplant of foetal cells to replace the damaged dopamine producing cells have led to hope that a cure may eventually be developed, but this is, as yet, not on the immediate horizon.