Parkinsonism: Symptoms and Defect
Parkinsonism is a progressive neurodegenerative disease that adversely affects motor neuron control. Major early symptoms are tremor at rest, bradykinesia, muscle rigidity, and flat facial affect. If untreated, the condition worsens, leading eventually to complete immobility and early mortality. The prevalence is approximately 2% in persons older than 65 years. A genetic predisposition seems likely, but environmental factors (including viral infections and neurotoxins) may play a role. The most distinctive neuropathologic finding is progressive loss of dopaminergic neurons of the pars compacta of the substantia nigra. Projections of dopaminergic neurons from the substantia nigra correlate with motor and cognitive deficits. Degeneration of dopaminergic neurons in the nigrostriatal tract causes loss of inhibitory dopamine action on striatal GABAergic neurons and leads to excessive cholinergic neuron excitation of these striatal neurons. Drugs such as levodopa (increases dopaminergic activity) can help.