An immunohistochemical study of neurofibrillary tangle formation in post-encephalitic Parkinsonism

Neurofibrillary tangle (NFT) formation is a feature of postencephalitic Parkinsonism (PEP) and Alzheimer's disease (AD). Tangle formation has been compared immunohistochemically in these 2 conditions. Staining patterns for tau protein, ubiquitin and beta/A4 amyloid protein were studied in frontal lobe, hippocampus, and midbrain in 2 classical cases of PEP, 2 cases of AD and 2 controls matched for age and sex. NFTs were present in all cases, but with varying frequency: all tangles were tau-positive and many were ubiquitinated. In the frontal cortex and hippocampus, irrespective of the case category, tangle formation was associated with beta/A4 amyloid deposition. A similar association was present in the 2 AD cases in the midbrain. However, in PEP tangle formation in the midbrain was not associated with adjacent beta/A4 amyloid deposition. This finding raises the possibility that the pathogenetic mechanism of tangle formation in PEP is different from that of AD, although the final cellular morphological expression of abnormality in both conditions is similar.