Parkinson's disease, which mostly affects older people but can occur at any age, results from the gradual degeneration of nerve cells in the portion of the midbrain that controls body movements. The first signs are likely to be barely noticeable -- a feeling of weakness or stiffness in one limb, perhaps, or a fine trembling of one hand when it is at rest. Eventually, the shaking worsens and spreads, muscles tend to stiffen, and balance and coordination deteriorate. Depression, cognitive issues, and other mental or emotional problems are common as well.
Parkinson's disease usually begins between the ages of 50 and 65, striking about 1% of the population in that age group; it is slightly more common in men than in women. Medication can treat its symptoms, and the disorder is not directly life-threatening.
Therapeutic interventions should begin in the early stages of the disease in order to enhance mobility and quality of life.
T Kuaffman, J Barr, M Moran; Geriatric Rehabilitation Manual 2nd Edition, 2007