"Grumose degeneration" of Trétiakoff.

We reviewed Trétiakoff's "grumose degeneration (GD)" which described pathologic cellular change in the substantia nigra (SN). This term has been occasionally used up to the mid-1960s by Greenfield et al.; it has rarely been used after the 1970s. This study emphasises the following: (1) after the 1970s, GD has sometimes been signalled in the SN under various names, such as "spheroid with foamy appearance", "granular spheroid", "saccular structure", or "foamy spheroid body"; (2) the ultrastructure of GD is unknown, being entirely different from that of typical axonal swellings (so-called "spheroids"); (3) more attention should be paid to GD in the SN because its nature has remained unclarified since the original description; and (4) "GD" in the cerebellar dentate nucleus is essentially different from Trétiakoff's GD.