Myokymia and the Motor Unit

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Abstract
A patient was seen who developed myokymia acutely. The electromyographic picture revealed the typical trains of motor unit potentials in the gastrocnemii at rest. A biopsy of the gastrocnemius muscle at a time when myokymia was present showed some interesting histochemical changes. A population of fibers was seen which was entirely depleted of glycogen. These were scattered throughout the biopsy and did not occur in clumps. In one region of the biopsy, the glycogen depleted fibers were all type IIA and in another area all were type IIB. Many type I fibers stained more darkly than usual with the PAS stain for glycogen. These results parallel experimental work in animals and suggest that in man muscle fibers of a given motor unit are uniform in histochemical type. It also suggests that subunits do not exist in man.