Malignant hyperthermia is a potentially life-threatening metabolic disorder that occurs primarily in dogs; however, it can also affect cats.
An autosomal dominant mutation documented in dogs results in sustained calcium release, which leads to persistent muscle contraction and subsequent elevation in body temperature (1).
The most common triggers of malignant hyperthermia appear to be volatile anesthetic agents (eg, halothane, isoflurane, sevoflurane) and depolarizing neuromuscular blocking agents (eg, succinylcholine). Stress, excitement, or exercise can also trigger episodes in some patients. A malignant hyperthermia–like syndrome has also been reported secondary to ingestion of hops (2).
Animals with malignant hyperthermia may show no clinical signs until an episode is triggered. Susceptible dogs sometimes have hypertrophied muscles, a hyperactive temperament, and a resting rectal temperature that is high-normal to slightly elevated. Serum CK activity might be mildly elevated.
An episode of malignant hyperthermia can occur minutes to a few hours after a triggering event, and clinical signs include the following:
tachypnea
tachycardia
fever
limb muscle rigidity
myoglobinuria
Severe metabolic acidosis can occur, and respiratory or cardiac arrest can happen quickly.
Diagnosis of malignant hyperthermia is through recognition of clinical signs during anesthesia. In anesthetized patients, increased CO2 production appears to be the earliest indicator.
Treatment consists of immediate cessation of potentially triggering anesthesia or neuromuscular blocking agents, in conjunction with hyperventilation with oxygen. Measures to lower body temperature (eg, IV fluid therapy, cool water lavage or enemas, and ice packs) are also used. IV fluids should not contain calcium. Dantrolene, a muscle relaxant that works by blocking calcium release, can be administered at 2–3 mg/kg, IV, as a bolus; boluses can be repeated until clinical signs subside, up to a cumulative dose of 10 mg/kg (3, 4, 5).
Dantrolene can also be used as a preventative in patients with previous episodes.
The prognosis for dogs and cats with malignant hyperthermia is guarded but may be improved by early recognition and treatment.
For other metabolic myopathies in dogs and cats, see the Overview for this chapter.
For More Information
Also see pet owner content regarding malignant hyperthermia in dogs and malignant hyperthermia in cats.
References
Roberts MC, Mickelson JR, Patterson EE, et al. Autosomal dominant canine malignant hyperthermia is caused by a mutation in the gene encoding the skeletal muscle calcium release channel (RYR1). Anesthesiology. 2001;95(3):716-725. doi:10.1097/00000542-200109000-00026
Becker J, Brutlag AG, Hovda L, Rendahl A, Tart KM. A retrospective evaluation of hops ingestion in 177 dogs (2005-2018). J Vet Emerg Crit Care (San Antonio). 2023;33(3):348-353. doi:10.1111/vec.13282
Brunson DB, Hogan KJ. Malignant hyperthermia: a syndrome not a disease. Vet Clin North Am Small Anim Pract. 2004;34(6):1419-1433. doi:10.1016/j.cvsm.2004.05.010
Chohan AS, Greene SA. Anesthesia case of the month. Malignant hyperthermia. J Am Vet Med Assoc. 2011;239(7):936-940. doi:10.2460/javma.239.7.936
Kirmayer AH, Klide AM, Purvance JE. Malignant hyperthermia in a dog: case report and review of the syndrome. J Am Vet Med Assoc. 1984;185(9):978-982.
