<unk>  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<unk> . Historically, starting in 1917 an epidemic of<unk>  lethargica, also called von Economo's<unk>  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<unk>  lethargica with influenza has been made. Although<unk>  was occasionally seen during the acute<unk>  phase of<unk>  lethargica, it was often encountered in the<unk><unk>  phase. The onset of<unk>  can be delayed by several years from the resolution of<unk>  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.
Post-encephalitic parkinsonism
Cerebellar cognitive affective syndrome
Dopamine-responsive dystonia
Paraneoplastic cerebellar degeneration
Early myoclonic encephalopathy
Progressive supranuclear palsy
Levodopa-induced dyskinesia
Glycine encephalopathy