We encountered an 83-year-old man with 3-repeat dominant grain-like tau deposition. Tau-positive lesions exhibited apparent similarity to argyrophilic grains in terms of their distribution in the ambient gyrus, amygdala, and dorsomedial temporal tip and the characteristic comma-like morphology. The abundant oligodendroglial tau immunoreactivities were 3-repeat dominant. Tuft-shaped astrocytes showed partial 3-repeat tau immnoreactivities. These grain-like structures, as well as tuft-shaped astrocytes and oligodendroglia, exhibited predominant 3-repeat tau immunoreactivity, suggesting that grain-like structures and their characteristic distribution are mutually linked and not unique to 4-repeat tau deposition. pTDP immunoreactivity, extensive macrophage infiltration, and spongiosis were associated with these 3-repeat tau deposits.
Keywords: 3-repeat tau; TDP-43; ambient gyrus; amygdala; astrocytic tau immunoreactivity; grain; oligodendroglial tau immunoreactivity; temporal tip.