Approximately 1% of individuals over 50 years of age are affected by Parkinson’s disease (PD), which is probably the most common cause of progressive motor dysfunction among the elderly.
Histologically, it is characterized by loss of pigmented dopaminergic neurons of the pars compacta portion of the substantia nigra as well as loss of pigmented cells within the locus ceruleus and the dorsal motor nucleus of the vagus. Reactive astrocytosis and eosinophilic cytoplasmic inclusions (Lewy bodies) may be present as well.
The characteristic clinical findings include tremors at rest, bradykinesis, masked facies, hypophonia, shuffling gait, stooped posture, and what is commonly described as the “cog-wheel” type of rigidity. These patients may develop dementia up to 30% of the time, which may be due to the presence of concurrent AD.
Narrowing of the pars compacta portion of the substantia nigra may be detected on MRI and is best appreciated on T2-weighted images. The changes are often bilateral; however, unilateral cases do exist.