Skeletal muscle characteristics of people with multiple sclerosis

To compare the single-fiber characteristics and muscle weakness of persons with multiple sclerosis (MS) with that of healthy persons without MS.

Descriptive.

A university-based exercise physiology laboratory.

Fourteen subjects (7 controls, 7 people with relapsing-remitting MS; Expanded Disability Status Scale median score, 6.0; range, 2.5-6.5).

Not applicable.

Singe muscle fiber myosin heavy chain (MHC) distribution, myosin adenosine triphosphatase fiber type, and single muscle fiber cross-sectional area (CSA).

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.

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.