Can secondary degeneration accelerate the formation of neurofibrillary tangles? A case of hemispheric infarction showing asymmetric degeneration of the substantia nigra, red nuclei, inferior olivary nuclei and dentate nuclei with concomitant changes of progressive supranuclear palsy.

A case of hemispheric infarction involving the territory of the right middle cerebral artery and the thalamus showed conspicuous asymmetric degeneration in the substantia nigra, red nuclei, inferior olivary nuclei and dentate nuclei with concomitant changes of progressive supranuclear palsy (PSP). The right substantia nigra and red nucleus showed loss of neurons and proliferation of astrocytes. The right olivary nucleus was hypertrophic, while the neuronal loss and astrocytosis in the dentate nucleus were predominant on the contralateral side. Modified Gallyas-Braak staining revealed the extensive distribution of neurofibrillary tangles (NFTs), threads and intraglial argyrophilic structures in the globus pallidus, subthalamic nuclei, cerebral cortex and dentate nuclei, as well as in the affected brain stem nuclei, with a distinct predominance on the affected side. In this case, the one-sided predominance of the extended degeneration in these brain stem and cerebellar areas is considered, in addition to the PSP changes, to be due to secondary retrograde degeneration via the nigrostriatal and dentato-rubro-thalamic pathways following the hemispheric infarction, and to also be the result of disruption of the dentato-olivary fiber connections. In addition, because of the predominant distribution of NFTs on the more degenerated side, it is surmised that the formation of NFTs may be accelerated by secondary degeneration.