Probable hypothyroid myopathy: glycogen-deficient type 2b fibers

Described herein is a case of hypothyroid myopathy with selective atrophy and glycogen depletion of type 2b fibers shown by light and electron microscopy. Although the pathogenesis of such findings is obscure, it is possible that hypothyroidism in conjunction with a superimposed process might explain paradoxically glycogen-deficient fibers.