AbstractBody components were measured noninvasively in patients with neuromuscular disease by using dual‐energy X‐ray absorptiometry (DXA), capable of separately analyzing fat, bone, and muscle content. In all patients with muscle atrophy of myogenic or neurogenic origin, muscle mass was markedly reduced. Although all three components (fat, muscle, and bone) were decreased in neurogenic atrophy patients, fat mass alone was increased significantly in myogenic atrophy patients. The fat/muscle ratio (f/m) was significantly higher in myogenic atrophy patients than in the normal controls and neurogenic atrophy patients. The higher f/m ratio in myogenic atrophy patients seems to reflect a marked fat infiltration into atrophied skeletal muscles of patients with primary muscular disease. Using DXA, it is possible to distinguish clearly between myogenic atrophy from neurogenic atrophy, opening the way to an evaluation of the severity of quantitative and qualitative muscle changes in neuromuscular disease. © 1994 John Wiley & Sons, Inc.