Pathological Findings of the Skeletal Muscles in a Racehorse Presenting with Malignant Hyperthermia-Like Symptoms after Halothane Anesthesia

Abstract

We performed pathological analysis of the skeletal muscles obtained from a racehorse that showed astasia after halothane anesthesia. Light microscopic examination revealed that skeletal muscle fibers had undergone degenerative changes such as coagulation necrosis, segmental rarefaction, and granular degeneration. Electron microscopic examination revealed damage of sarcomeres. Fragmentation of the actin filaments without Z-discs degeneration was seen in some areas in which rarefaction was observed under a light microscope. Electron microscopic examination demonstrated degenerated muscle fibers, which are commonly observed during the process of skeletal muscle degeneration. However, we also observed marked degeneration of the actin filaments. This change differed from the myofibril degradation process, explained so far, suggesting the existence of a mechanism by which actin filaments are predominantly degraded.