The muscle biopsy in AMC is diagnostic in the rare myopathies that cause AMC and in cases of denervation atrophy (provided an affected muscle is sampled). Denervation changes include classic individual or group myofiber atrophy. A significant proportion of biopsies show type 1 fiber predominance , which is probably the end result of denervation and collateral reinnervation. In the rest of AMC cases the muscle biopsy shows nonspecific findings such as myofiber atrophy and replacement of lost muscle with fibroadipose tissue. In some cases, muscle wastes so that only fibroadipose tissue remains. This probably gave rise to the notion of amyoplasia (., agenesis or absence of development of muscle). The term amyoplasia is used in literature to identify a clinical subset of AMC, not as a pathological diagnosis. There is no evidence of agenesis of muscle in AMC cases with detailed pathological studies.