Becker and Duchenne muscular dystrophy: a comparative morphological study

It is important to be able to clearly differentiate between Duchenne (DMD) and Becker (BMD) muscular dystrophies in early childhood in order to offer more accurate prognostic information to parents. In response to this need, biopsies from BMD and DMD patients were compared to see which features, if any, allowed a differentiation to be made. Fifteen biopsies of vastus lateralis muscle from boys with the mild (BMD) X-linked muscular dystrophy were compared with 19 biopsies from patients with the severe (DMD) form using a variety of histochemical and morphometric parameters. Both forms showed many similarities including increases in fibre variation, percentages of Type 1 fibres, internal nuclei counts, split and fragmented fibres and groups of fibres attempting regeneration. Hypercontracted and necrotic fibres, interstitial inflammatory cells and endomysial connective tissue were more commonly increased in DMD. Fibre hypertrophy was initially prominent, particularly in DMD boys until 5 years of age and in BMD patients until approximately 10 years, thereafter the mean fibre sizes became smaller than normal. Type 2B deficiency was again common in DMD as well as occurring in some BMD cases. Nuclear aggregates and small group atrophy were more likely to be found in BMD. In the absence of morphological criteria to accurately discriminate between DMD and BMD, classification of young affected males with muscular dystrophy into one or other groups, remains a difficulty in the first decade of life.