Motor innervation and fiber type pattern in amyotrophic lateral sclerosis and in Charcot‐Marie‐Tooth disease

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Abstract
A quantitive study of the terminal innervation ratio (TIR) was conducted using 18 amyotrophic lateral sclerosis (ALS) and 12 Charcot‐Marie‐Tooth disease (CMT) muscle biopsies. Morphometric and histochemical analyses of muscle fibers were performed in 9 ALS and 6 CMT biopsies. The results revealed that TIR and type grouping were significantly greater in CMT than in ALS. The proportion of type 3 fibers was higher in ALS, though the proportion of intermediate and type 0 fibers was significantly higher in CMT. The atrophy factor was significantly greater in type 3 than in types 1 and 2 fibers, but it was not significantly different in type 0 and intermediate fibers as compared to types 1 and 2. It appears, therefore, that CMT has a better capacity for collateral reinnervation than ALS. Type 0 and intermediate fibers may represent altered endproducts of successful collateral reinnervation.