Progress and Prospects in Parkinson's Research/Monitoring Parkinson's Disease/Measurement of Parkinson's Disease Progression/What is PD?

The Wikipedia entry for Parkinson's disease says that "the most obvious symptoms are motor-related, including tremor, rigidity, slowness of movement, and postural instability".

But also in its first paragraph it indicates that there are also many non-motor symptoms of this "degenerative disorder of the central nervous system that impair motor skills, cognitive processes, and other functions."

Therefore an adequate description of the disease and the characteristics of its progression must recognise that it involves the degeneration of centres beyond merely those that control movement. Indeed the loss of dopamine signalling and the appearance of movement disorders due to the degeneration of the cells of the substantia nigra are believed to be a comparatively late stage of the disease. "..Recent evidence of Lewy body pathology in other neuronal populations preceding nigral involvement suggests that the preclinical phase may be much longer." The authors of reference 2 cite evidence of impairment of a variety of areas of both the central and peripheral nervous systems, perhaps on occasion as early as 20 years before motor symptoms appear, that give rise, amongst other things, to constipation, anxiety disorders, rapid eye movement sleep behaviour disorder (RBD), anaemia, olfactory impairment and depression.

The characteristic pathology of the affected parts of the nervous system, whether central or peripheral, involves the aggregation of the protein alpha-synuclein. .  This suggests that Parkinson's disease is more usefully understood in terms of its extensive alpha-synuclein pathology rather than the overt symptoms in which movement dysfunction tends to take centre stage. (But see and )