Ring fibers visualized by electron microscopy in a Japanese patient with malignant hyperthermia.

This report describes an episode of malignant hyperthermia (MH) in a 53-year-old Japanese man during general anesthesia that was triggered by isoflurane and succinylcholine. His past history and family history were unremarkable. From our analysis of ten exons, he had no recognizable mutation in the ryanodine receptor gene, but compatible with his MH reaction, he showed positive sensitivity to the Ca-induced Ca-release test. Histochemical and electron microscopic studies of muscle biopsy tissue demonstrated unusual "ring fibers," which have never before been reported to be associated with MH. The presence of ring fibers in this patient might indicate muscle regeneration, suggesting a recovery process from the MH episode.