What is Parkinson's Disease?

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Parkinson’s disease is a progressive brain disorder named after James Parkinson, M.D., the British physician who first described its symptoms in 1817. It is referred to as a movement disorder because it causes a shaking of the hands and other body parts referred to as a tremor, overall slowing of body movements, and muscle stiffness.

It affects about 1.5 million people in the United States, many of whom eventually suffer from memory loss, dementia, hallucinations and delusions.

If you have Parkinson’s disease, cells in the area of the brain called the substantia nigra fail to produce enough dopamine, a substance necessary for smooth and coordinated movements. This loss of dopamine leads to the signature symptoms of Parkinson’s disease: rhythmical shaking (tremor), stiffness, shuffling, slowness of movement, balance problems, small or cramped handwriting, loss of facial expression and soft, mumbled speech.

Although Parkinson’s disease is often thought of as a neurological disorder affecting movement, and these symptoms are the clinical hallmarks of a diagnosis of Parkinson’s disease, it is also associated with a sometimes disabling, often overlooked non-movement psychological condition known as cognitive impairment. This non-movement impairment can affect memory and attention span as well as the ability to plan and organize. Some patients already have some evidence of cognitive impairment when first diagnosed, and as the disease advances, the ability to recognize people and objects and communicate with others may become increasingly difficult, especially in the later stages.

Now that researchers and clinicians are aware of the effects of Parkinson’s disease on thinking and memory, many experts believe that nearly all patients will ultimately develop some degree of cognitive impairment.

Diagnostic challenges

Diagnosing cognitive impairment in Parkinson’s disease patients is made challenging by the fact that it is often difficult to determine whether certain symptoms are due to Parkinson’s disease or another disorder. For instance, slowed response time could also be a complication of Alzheimer’s disease. And significant cognitive impairment could arise from Lewy body dementia rather than Parkinson’s or Alzheimer’s disease.

Lewy body dementia is associated with the abnormal accumulation in the brain of the protein alpha-synuclein. Its function in healthy brains is still unknown, but it’s of great interest to researchers because it forms protein clumps that are a hallmark of Parkinson’s. Scientists now believe that Lewy body dementia—rather than Alzheimer’s disease—is responsible for many cases of dementia in patients with Parkinson’s disease.

Treating patients with Parkinson’s disease when there are no signs of cognitive impairment is already a complex task. But treating patients with Parkinson’s disease when evidence of cognitive impairment is present is even more complicated. Some medications commonly used to treat classic Parkinson’s disease, such as levodopa and dopamine agonists, can worsen cognitive impairment and increase hallucinations, delusions and agitation. This is especially true in patients with Parkinson’s disease who also have dementia.

Treating psychotic symptoms with antipsychotic medication (neuroleptics) is also complicated because most of these drugs block dopamine receptors in order to improve hallucinations and delusions, which, in turn, can further impair the movement disorder caused by the primary dopamine deficiency of Parkinson’s.