Morphological changes of motor units in Duchenne's muscular dystrophy.

We studied the intramuscular motor innervation in 19 muscle biopsy specimens from boys with Duchenne's muscular dystrophy and the fiber-type pattern was analyzed in nine biopsy specimens. The main change in motor innervation was a longitudinal displacement of motor end plates that could reach 10 mm and the presence of numerous unemployed axons ending freely within connective tissue. There was no increased collateral ramification of subterminal axons and the terminal innervation ratio was normal. The fiber-type pattern was characterized by a random variation of fiber diameters, a slight predominance of type 1 fibers, and an impared type differentiation in many fibers. The morphological data do not support the possibility of denervation and collateral reinnervation that could be related to the late component potentials found in Duchenne's muscular dystrophy.