Postanesthetic equine myopathy suggestive of malignant hyperthermia. A case report.

This study focuses on an equine case featuring signs of malignant hyperthermia, a dangerous reaction to certain medications used during general anesthesia. The researchers noted a halothane-anesthetized horse developed symptoms like increased carbon dioxide levels, increased skin temperature, heart rate, and elevated potassium, phosphate, and creatine kinase levels. After halting the halothane inhalation and providing treatments like cooling and oxygen hyperventilation, the horse recovered initially but subsequently developed myopathy affecting both hind legs and pigmenturia. The condition was improved with oral dantrolene, IV fluids, and hydrocortisone. Eventually, muscle tests were performed and deemed normal, but the root cause of the post-anesthetic myopathy remains unidentified.

Study Objectives

• The primary purpose of this research was to analyze an anomaly in equine medicine, where a horse displayed indicators of malignant hyperthermia post-anesthetic recovery. The investigators aimed to understand if these signs could predict myopathy occurring after anesthesia.

Methods

• The horse was under halothane anesthesia when it began to show clinical symptoms of malignant hyperthermia: surging levels of carbon dioxide (PaCO2), body temperature, and heart rate, and amplified serum concentrations of potassium, inorganic phosphate, and creatine kinase.
• Reactively, halothane administration was stopped immediately, the horse was intensely cooled with ice and cold fluids, and hyperventilated with 100% oxygen. This helped in primary recovery.
• However, the recovery was marred with the onset of bilateral hindlimb myopathy (muscle disease) and pigmenturia (presence of pigments in urine).
• The research team treated the myopathy employing oral dantrolene, intravenous fluids, and hydrocortisone leading to its resolution.
• Finally, a caffeine-halothane challenge was conducted on muscle tissue from the horse, procured two weeks after the episode. The results of the test fell within expected parameters for horses, suggesting normal muscle function.

Conclusions

• The intraoperative abnormalities proved predictive of potential postanesthetic myopathy. In other words, particular anomalies occurring during the operation were determining factors or signals for the likelihood of the horse developing the muscle disease after the anesthesia.
• Despite the rigorous steps taken to manage and comprehend the situation, the root cause behind the case of postanesthetic myopathy in this horse remains elusive. This mystery encourages further investigation to uncover the underlying trigger of such occurrences.