Treatment of Parkinson's disease

Pharmacotherapy with levodopa for Parkinson's disease provides symptomatic benefit, but fluctuations in (or loss of) response may eventually occur. Dopamine agonists are also helpful and, when taken with low doses of levodopa, often provide sustained benefit with fewer side effects; novel agonists and new methods for their administration are therefore under study. Other therapeutic strategies are being explored, including the use of type B monoamine oxidase inhibitors to reduce the metabolic breakdown of dopamine, catechol-O-methyltransferase inhibitors to retard the breakdown of levodopa, norepinephrine precursors to compensate for deficiency of this neurotransmitter, glutamate antagonists to counteract the effects of the subthalamic nucleus, and various neurotrophic factors to influence dopaminergic nigrostriatal cells. Surgical procedures involving pallidotomy are sometimes helpful. Those involving cerebral transplantation of adrenal medullary or fetal mesencephalic tissue have yielded mixed results; benefits may relate to the presence of growth factors in the transplanted tissue. The transplantation of genetically engineered cell lines will probably become the optimal transplantation procedure. The cause of Parkinson's disease may relate to oxidant stress and the generation of free radicals. It is not clear whether treatment with selegiline hydrochloride (a type B monoamine oxidase inhibitor) delays the progression of Parkinson's disease, because the drug also exerts a mild symptomatic effect. Daily treatment with vitamin E (a scavenger of free radicals) does not influence disease progression, perhaps because of limited penetration into the brain.