Muscle CT scans in preclinical cases of Duchenne and Becker muscular dystrophy

Skeletal muscle CT scans were performed in patients with Duchenne (DMD) as well as Becker muscular dystrophy (BMD) in the preclinical or early clinical stage, at the levels of the 3rd lumbar vertebra, the mid thigh, and the maximum circumference of the calf. Only slight intramuscular low density areas and muscular atrophy were ascertained on gross visual inspection from the age of 3 years onward in DMD. However, the mean CT numbers calculated for individual muscles clearly decreased with increasing age in all muscles except anterior and posterior tibialis, which indicated them to be well preserved. Comparison of the rates of decrease in the CT numbers revealed that a rapid change in the paravertebral group commenced in the muscles on the lateral side, while among the adductors of the thigh, gracilis tended to be comparatively well preserved; this is the pattern of muscle involvement characteristic of symptomatic patients. In BMD, the atrophic change was extremely slight, and the CT numbers of the muscles were higher than the corresponding values for DMD in the same age group. CT numbers represent more objective indices for the assessment of muscular lesions as compared with gross visual inspection of skeletal muscle CT scans at the preclinical stage.