A glucose-6-phosphate dehydrogenase stain for frozen human skeletal muscle biopsy specimens. A sensitive indicator of fiber degeneration.

The glucose-6-phosphate dehydrogenase (G6PD) stain was adapted to skeletal muscle by using homogenate assays and quantitative cytochemical stains to determine the "correct" localization. For both feline and human skeletal muscles, the appropriate level of phenazine methosulfate eliminated fiber typing, which was falsely localizing the rate-limiting, bound reduced form of NADPH rather than the soluble G6PD. Use of a viscous solution of polyvinyl alcohol was necessary to prevent enzyme diffusion. Under these conditions, G6PD produced a mild myoplasmic stain with even sarcoplasmic reticulum granularity in human biopsy specimens. Fibers that were degenerating or regenerating by hematoxylin-eosin or alkaline phosphatase stains yielded an intense myoplasmic G6PD stain. Additional degenerating fibers were also often detectable with G6PD staining. No increased staining was found in denervated or atrophic fibers. Absence of staining (after 2 hours) was not a reliable indicator of G6PD deficiency, although it could be used for preliminary screening of muscle biopsy specimens.