… In the parkinsonian syndrome occur the typical lesions of encephalitis, perivascular cell infiltration, hemorrhages, exudation, areas of degeneration, and destruction of nerve cells. These lesions occur in many and diverse parts of the central nervous system, but the basal ganglions bear the brunt of the attack. There is also an atrophy and reduction in the number of cells, together with a depigmentation, of a particular part of the brain; namely, the substantia nigra.
There have not been a large number of necropsies performed in cases of the parkinsonian syndrome. We were surprised to find not more than twenty-five. McAlpine has reviewed the literature and cited the opinions of all who have studied the subject. Three quarters or more of these authorities are unanimous in asserting that in the parkinsonian syndrome a characteristic injury has been sustained by the substantia nigra. They point out that in every necropsy this particular nucleus is affected, and affected in a characteristic way. They report a reduction of its cells, an atrophy of the remaining ones, and a destruction and disintegration of the nuclear pigment. From this, they reason that in that particular nucleus is situated the lesion of the parkinsonian syndrome.
Livingston Hunt E, Cornwall LH. The Postencephalitic Parkinson Syndrome. JAMA. 2014;311(16):1696. doi:10.1001/jama.2013.279467