Parkinson's disease (PD) is a degenerative disorder of the central nervous system mainly affecting the motor system. Early in the course of the disease, the most obvious symptoms are movement-related; these include shaking, rigidity, slowness of movement and difficulty with walking and gait. Later, thinking and behavioral problems may arise, with dementiacommonly occurring in the advanced stages of the disease, and depression being the most common psychiatric symptom. Other symptoms include sensory, sleep, and emotional problems. The main motor symptoms are collectively called "parkinsonism", or a "parkinsonian syndrome".
The disease can be either primary or secondary. Primary Parkinson's disease has no known cause, although some atypical cases have a geneticorigin. Secondary parkinsonism is due to known causes like toxins. Many risks and protective factors have been investigated: the clearest evidence is for an increased risk in people exposed to certain pesticides and a reduced risk in tobacco smokers. The motor symptoms of the disease result from the death of cells in the substantia nigra, a region of the midbrain. This results in not enough dopamine in these areas. The reason for this cell death are poorly understood but involves the build-up of proteins into Lewy bodies in the neurons. Where the Lewy bodies are located is partly related to the expression and degree of the symptoms. Diagnosis of typical cases is mainly based on symptoms, with tests such as neuroimaging being used for confirmation. Treatments, typically the antiparkinson medications L-DOPA and dopamine agonists, improve the early symptoms of the disease. As the disease progresses and neurons continue to be lost, these medications become ineffective while at the same time produce a complication marked by involuntary writhing movements. Diet and some forms of rehabilitation have shown some effectiveness at improving symptoms. Surgery to place deep brain stimulation have been used to reduce...