Multiple sclerosis is well defined clinically by signs and symptoms referable to almost any part of the central nervous system. Pathologically, it is characterized by numerous plaques scattered throughout the neural axis and involving essentially the white matter. The main feature of the plaque is the destruction of the myelin sheaths, with some sparing of the axis-cylinders and ganglion cells, and a replacement of the destroyed parenchyma by an excessive increase in glia. Occasionally cases of this protean disease are encountered which do not conform to the classic description and which offer diagnostic difficulties, such as those marked by the atrophy of muscles. Of a series of 20 cases of multiple sclerosis which came to necropsy, 12 showed atrophy of one or more groups of muscles or of a whole extremity; atrophies of this nature also occurred in 17 of 110 other cases of multiple sclerosis observed clinically at Montefiore