Pick-body-like inclusions in corticobasal degeneration differ from Pick bodies in Pick's disease

In corticobasal degeneration (CBD), tau-positive cytoplasmic inclusions resembling Pick bodies (PBs) appear in the cerebral cortex. Tau immunoreactivity in PBs is expressed mainly on filamentous elements, whereas that of PB-like inclusions in CBD is expressed on granules, which are densely packed mainly in the periphery of inclusions. PBs are clearly detectable by conventional Bodian silver impregnation but negative for the Gallyas-Braak (G-B) method and for PS262, which recognizes phosphorylation at Ser 262 of the entire tau sequence. Almost all PBs are negative for Ex10, which recognizes 4-repeat tau specifically. In contrast to PBs, PB-like inclusions in CBD could not be detected by the Bodian method, but were positive for the G-B method, PS262 and Ex10. In summary, PBs and PB-like inclusions exhibit distinct differences. These results are useful for the argument of an overlap between PiD and CBD as well as discussion of the phenotypic resemblance of PB-like inclusions bearing types of FTDP-17 to Pick's disease.