Parkinson’s disease [James Parkinson] , a slowly progressive degenerative neurological disorder characterized by resting tremor, pill rolling of the fingers, a masklike facies, shuffling gait, forward flexion of the trunk, loss of postural reflexes, and muscle rigidity and weakness. It is usually an idiopathic disease of people over 60 years of age; it may occur in younger people, however, especially after acute encephalitis or carbon monoxide or metallic poisoning, particularly by reserpine or phenothiazine drugs. Typical pathological changes are destruction of neurons in basal ganglia; loss of pigmented cells in the substantia nigra; and depletion of dopamine in the caudate nucleus, putamen, and pallidum, structures in the neostriatum that normally contain high levels of the neurotransmitter dopamine. Signs and symptoms of Parkinson’s disease, which include resting tremor, bradykinesias, drooling, increased appetite, intolerance to heat, oily skin, emotional instability, and defective judgment, are increased by fatigue, excitement, and frustration. Palliative and symptomatic treatment of the disease focuses on correcting the imbalance between depleted dopamine and abundant acetylcholine in the striatum because dopamine normally appears to inhibit excitatory cholinergic activity in this brain area. Levodopa, a dopamine precursor that crosses the blood-brain barrier, may be used, but many patients experience side effects, such as nausea, vomiting, insomnia, orthostatic hypotension, and mental confusion. Carbidopa-levodopa, which contains an inhibitor of the enzyme dopa decarboxylase, limits peripheral metabolism of levodopa and thus causes fewer side effects. Anticholinergic drugs, such as benztropine mesylate, biperiden, procyclidine, and trihexyphenidyl, may be used as therapeutic agents but often cause ataxia, blurred vision, constipation, dryness of the mouth, mental disturbances, slurred speech, and urinary urgency or retention. Amantadine hydrochloride, an antiviral drug with antiparkinsonian activity, promotes the accumulation of dopamine in extracellular or synaptic sites, but the therapeutic effectiveness may not last more than 3 months in some patients; side effects, such as mental confusion, visual disturbances, and seizures, occur infrequently. Also called paralysis agitans.
