Malignant hyperthermia (MH) is a subclinical myopathy in which general anesthesia triggers an uncontrollable contraction of skeletal muscle that leads to a life-threatening hypercatabolic state and increase in body temperature. The disease is primarily autosomal dominant; mutations in receptors (especially ryanodine receptor type 1) predispose to volatile anesthetic agents or succinylcholine causing an accumulation of intracellular calcium in skeletal muscle that leads to its overactivation and hypermetabolism. In the acute setting, diagnosis is based mainly on clinical presentation and end-tidal capnography, which reveals an increase in end-tidal CO2. Immediate treatment measures involve stopping the triggering agent and administration of dantrolene. In nonacute settings, there are specific diagnostic tools (e.g., caffeine halothane contracture test) to confirm suspected cases. MH is a lethal disease and has a high mortality rate if left untreated.
Epidemiological data refers to the US, unless otherwise specified.
- Inherited susceptibility: primarily autosomal dominant with reduced penetrance
- Triggering agents
Administration of triggering substances → calcium release from intercellular compartments or delay in its reuptake → ↑ calcium in muscle cells → ↑ contractility of the skeletal muscle → ↑ metabolism → ↑ oxygen consumption in addition to ↑ CO2 production, heat, and lactate (malignant hyperthermia) → mixed respiratory and metabolic acidosis → uncoupled oxidative phosphorylation → breakdown of the cell's energy supply → cell death
- Early signs
- Late signs
Although the rise in body temperature is usually a late sign in malignant hyperthermia, it may occur as an early sign in severe cases!
The diagnosis is based on clinical presentation (e.g., muscle and jaw rigidity, hyperthermia) with an increase in end-tidal CO2 and signs of muscle breakdown. Confirmatory tests are reserved for stabilized patients and to prophylactically investigate those with a positive family history.
- See differential diagnosis of drug-induced hyperthermia.
- Acute porphyria crisis
- Levodopa withdrawal syndrome
The differential diagnoses listed here are not exhaustive.
- Discontinuation of potential triggering agents
Immediate administration of dantrolene (ryanodine receptor antagonist)
- Mechanism of action
- Adverse effects
- Cooling measures (e.g., ice packs, cool water blankets, ice-water immersion, IV iced saline, forced air cooling) 
- Increase respiratory minute volume by at least 3-fold.
- Ventilation with 100% O2
- Expedited completion of surgery
Dantrolene directly deals with distressed muscle.