Enzyme histochemistry of skeletal muscle. 3. Neurogenic muscular atrophies.

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Abstract
There are 2 fiber types in human skeletal muscle. Type-I fibers are rich in certain oxidative enzymes such as reduced nicotinamide adenine dinucleatide (NADH) diaphorase and poor in phosphorylase and type-D rich in phosphorylase and adenosine triphosphatase (ATPase) but poor in oxidative enzymes. Muscle biopsies from 7 patients with severe infantile spinal muscular atrophy (Werdnig-Hoffmaim''s disease) and from 8 patients with benign infantile spinal muscular atropy were studied by enzyme hlstochemistry. The small atrophic fibers demonstrated strong and weak reactions for a particular enzyme in both groups of patients indicating that the atrophy was one of fully differentiated mature muscle and not arrested development of embryonic muscle. If a case of Wardnig-Hoffmaim''s disease is paralyzed at birth, atrophy probably started after the 26th wk. of gestation. A preponderance of type-H fibers was seen in the majority of biopsies. Large fibers showing a uniformly strong staining reaction for both phos-phorylase and NADH diaphorase were seen in some biopsies suggesting that both enzyme systems may have a pattern of uniform activity in the early fetal stages. It Is unlikely that these large fibers correspond to Wohlfart ''b'' fibers. Histochemically the large fibers are type-H and, the WohlJEart V fibers are type-I. These large fibers appeared in large groups or even whole bundles in some biopsies. Wohlfart ''b'' fibers which form a small proportion of the total fibers are scattered singly throughout the muscle instead of appearing in clusters. Abnormally large fibers are not seen in the experimental animal probably due to the totality of denervation. The denervation is slow in the human.