Facioscapulohumeral muscular dystrophy: muscle fiber type analysis with particular reference to small angular fibers.

Muscle biopsies from 14 patients with facioscapulohumeral muscular dystrophy (FSHD) aged from 5 to 45 years were studied histochemically with fiber type analysis, focusing on small angular fibers (SAF) to clarify their significance. There were no duration-related or age-dependent histopathological differences between child and adult patients. Variations in fiber size and SAF were observed in all, myonecrosis with occasional phagocytosis in 10 and regenerating fibers in 12 biopsies. Cellular responses including inflammatory cell infiltration (7 biopsies) and connective tissue proliferation (8 biopsies), and fiber architectural changes (9 biopsies) were additional common findings. Although SAF are also commonly seen in patients with Kugelberg-Welander disease and amyotrophic lateral sclerosis, in FSHD they were mostly type 2C fibers which frequently exhibit alkaline phosphatase-positive activity. Therefore SAF in FSHD are mostly the products of a regeneration rather than denervation process.