Post-encephalitic parkinsonism
Post-encephalitic parkinsonism is a disease believed to be caused by a viral illness that triggers degeneration of the nerve cells in the substantia nigra. Overall, this degeneration leads to clinical parkinsonism.
Historically, starting in 1917 an epidemic of encephalitis lethargica, also called von Economos encephalitis or "sleepy-disease" occurred, possibly related to the 1918 Spanish flu pandemic; however, even with the use of modern molecular diagnostic tests on appropriate corpses, no firm link between encephalitis lethargica with influenza has been made.  Although parkinsonism was occasionally seen during the acute
encephalitic phase of encephalitis lethargica, it was often encountered in the post-encephalitic phase. The onset of post-encephalitic
parkinsonism can be delayed by several years from the resolution of encephalitis lethargica.
The brain regions affected contain neurofibrillary tangles, similar to those seen in Alzheimers disease. Nevertheless, the senile plaques common in Alzheimers disease are not found.

References
Evidente V, Gwinn K (1998). "Post-encephalitic parkinsonism". J Neurol Neurosurg Psychiatry. 64 (1): 5. doi:10.1136/jnnp.64.1.5. PMC 2169890. PMID 9436719.


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