Skeletal muscle characteristics of people with multiple sclerosis

Objective: To compare the single-fiber characteristics and muscle weakness of persons with multiple sclerosis (MS) with that of healthy persons without MS. Design: Descriptive. Setting: A university-based exercise physiology laboratory. Participants: Fourteen subjects (7 controls, 7 people with relapsing-remitting MS; Expanded Disability Status Scale median score, 6.0; range, 2.5-6.5). Interventions: Not applicable. Main Outcome Measures: Singe muscle fiber myosin heavy chain (MHC) distribution, myosin adenosine triphosphatase fiber type, and single muscle fiber cross-sectional area (CSA). Results: The distribution of MHC I, MHC IIa, MHC IIx, and total hybrid fibers (I/IIa+I/IIa/IIx+IIa/IIx) did not differ between the 2 groups. However, the distribution of MHC I/IIa/IIx fibers was greater (P<.040) in the MS group (MS: 6% vs controls: 2%). MS subjects also had a greater proportion (P<.002) of MHC IIx-dominant IIa/IIx fibers (MS: 46% vs controls: 13%). Single-fiber CSA and fiber type, for all fiber types, did not differ between groups. Conclusions: These data suggest that, in general, moderately impaired MS subjects with documented muscle weakness have similar MHC and fiber-type characteristics as age-matched sedentary controls. The data indicate that the quality of skeletal muscle, with regard to MHC distribution, is unaffected by MS.