Does a long preclinical period occur in Parkinson's disease?

Parkinson's disease is a neurological disease which involves the selective destruction of some brain cells preferentially over others. The brain is able to compensate for considerable damage, and the available evidence suggests that the symptoms of Parkinson's disease appear only after the destruction of neurons (nerve cells) surpasses the brain's ability for compensation. Parkinson's disease largely results from the destruction of special brain cells within a region called the substantia nigra; by some estimates as many as 90 percent of these neurons may be destroyed before the brain can no longer compensate and disease symptoms appear. Therefore, the disease is present, and destroying neurons in the substantia nigra, long before it is recognized by the patient and physician. Evidence is accumulating that the drug selegiline may significantly slow the progression of Parkinson's disease, and so the initiation of treatment prior to the onset of symptoms might provide important clinical benefit. Just how long is Parkinson's disease present before the symptoms actually appear? Since there is no reliable test for the presence of Parkinson's disease, there is no way of answering with certainty. However, estimates may be made on the basis of neuropathological observations of brain tissue specimens obtained at autopsy. The characteristic pathological observation in Parkinson's disease is the Lewy body, which is a structure visible in the cytoplasm of some brain cells under the microscope. Lewy bodies are also found in cells of the substantia nigra of about 10 percent of people over age 60 who do not have symptoms of Parkinson's disease. If the assumption is made that Lewy bodies represent an early stage in the long progression towards brain cell destruction, then calculations suggest that the delay between the appearance of Lewy bodies and the development of the symptoms of Parkinson's disease must be about 30 years. The cells of the substantia nigra may be examined, of course, only at autopsy, and so other means must be found to diagnose Parkinson's disease in its presymptomatic stages. The search is underway to evaluate many techniques of medical imaging, biochemical analysis, and genetic screening for the diagnosis of presymptomatic Parkinson's disease. (Consumer Summary produced by Reliance Medical Information, Inc.)