Postencephalitic Parkinson entities

Clinic

• It 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 Economo's 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 Alzheimer's disease. Nevertheless, the senile plaques common in Alzheimer's disease are not found.