What is the most likely diagnosis for a horse with rhabdomyolysis and a temperature of 107°F during gas anesthesia?

What is the most likely diagnosis for a horse with rhabdomyolysis and a temperature of 107°F during gas anesthesia?

• A. Malignant hyperthermia
• B. Heat stroke
• C. Tetanus
• D. Myositis

Answer: (A)

Extreme hyperthermia occurring during gas anesthesia with associated rhabdomyolysis is classic for malignant hyperthermia in horses. In susceptible horses, exposure to volatile inhaled anesthetics triggers an abrupt, uncontrolled release of calcium in skeletal muscle, causing sustained muscle contraction, rapid metabolism, and enormous heat production. The result is a rapid rise in body temperature and widespread muscle breakdown, which fits the scenario of a 107°F fever during anesthesia. Heat stroke would require environmental or heat exposure to cause the fever, not an anesthetic context. Tetanus causes muscle rigidity from a toxin but isn’t driven by anesthesia and doesn’t typically present with such an acute, anesthesia-associated temperature spike. Myositis can involve muscle inflammation and rhabdomyolysis, but it doesn’t explain the sudden hyperthermic crisis triggered by inhaled anesthesia. So the extreme intraoperative fever with rhabdomyolysis points to malignant hyperthermia.

Extreme hyperthermia occurring during gas anesthesia with associated rhabdomyolysis is classic for malignant hyperthermia in horses. In susceptible horses, exposure to volatile inhaled anesthetics triggers an abrupt, uncontrolled release of calcium in skeletal muscle, causing sustained muscle contraction, rapid metabolism, and enormous heat production. The result is a rapid rise in body temperature and widespread muscle breakdown, which fits the scenario of a 107°F fever during anesthesia.

Heat stroke would require environmental or heat exposure to cause the fever, not an anesthetic context. Tetanus causes muscle rigidity from a toxin but isn’t driven by anesthesia and doesn’t typically present with such an acute, anesthesia-associated temperature spike. Myositis can involve muscle inflammation and rhabdomyolysis, but it doesn’t explain the sudden hyperthermic crisis triggered by inhaled anesthesia.

So the extreme intraoperative fever with rhabdomyolysis points to malignant hyperthermia.