Does muscular dystrophy increase the risk of malignant hyperthermia?

Muscular Dystrophy and Malignant Hyperthermia Risk

Patients with muscular dystrophy, particularly Duchenne (DMD) and Becker (BD), do NOT have an increased risk of true malignant hyperthermia, but they ARE at high risk for a life-threatening malignant hyperthermia-like syndrome that mimics MH and requires the same urgent avoidance of triggering anesthetic agents. 1

Critical Distinction: MH-Like Syndrome vs. True MH

DMD and malignant hyperthermia are genetically distinct diseases. 1 The key understanding is:

• True MH susceptibility is caused by mutations in the ryanodine receptor (RYR1) or calcium channel genes (CACNA1S), occurring in approximately 1:2,000 to 1:3,000 individuals 2, 3
• Muscular dystrophies result from dystrophin gene defects, not RYR1 mutations 4, 5
• Systematic analysis found no increased risk of true MH susceptibility in DMD/BD patients compared to the general population 4

However, one older study using contracture testing found positive results in 2 of 5 DMD patients and 1 of 2 BMD patients 6, though this conflicts with more recent systematic reviews 4.

The Life-Threatening MH-Like Syndrome

Despite being genetically distinct, patients with DMD are at increased risk for extreme hyperthermic events and rhabdomyolysis when exposed to certain anesthetics, especially inhaled agents such as halothane, isoflurane, and sevoflurane. 1 This syndrome:

• Mimics malignant hyperthermia clinically with hyperthermia, rhabdomyolysis, hyperkalemia, and potential cardiac arrest 1, 4
• Can occur intraoperatively or postoperatively 4, 5
• Has caused sudden death from hyperkalemic cardiac arrest in previously undiagnosed DMD patients 1
• Results from disruption of unstable dystrophic muscle cell membranes rather than true MH pathophysiology 4, 5

Absolute Contraindications in Muscular Dystrophy

Succinylcholine

Succinylcholine is absolutely contraindicated in patients with DMD and BD. 1, 4 This depolarizing muscle relaxant:

• Disrupts unstable cell membranes in dystrophic muscle 1
• Causes acute rhabdomyolysis, life-threatening hyperkalemia, and cardiac arrest 1, 4
• Has been linked to sudden death in young patients with previously unsuspected DMD 1

Inhaled Anesthetic Agents

Inhaled anesthetic agents should be considered contraindicated for patients with DMD. 1 These agents:

• Include halothane, isoflurane, sevoflurane, and desflurane 1
• Can trigger disease-related cardiac complications or the MH-like syndrome 4
• May cause rhabdomyolysis even in the absence of succinylcholine 4

Clinical Management Algorithm

Preoperative Evaluation

For any patient with known or suspected muscular dystrophy requiring anesthesia:

1. Obtain mandatory anesthesiology and pulmonology consultations before any procedure 1
2. Perform comprehensive pulmonary evaluation: FVC, MIP, MEP, PCF, and SpO2 in room air 1
3. Refer to cardiology for clinical evaluation and optimization of cardiac therapies 1
4. Discuss advance directives and resuscitation parameters preoperatively, as DMD is progressive and potentially fatal 1

Anesthetic Technique Selection

Use total intravenous anesthesia (TIVA) with non-triggering agents exclusively. 1 This approach:

• Avoids all volatile inhaled anesthetics 1
• Eliminates succinylcholine from the anesthetic plan 1
• Uses non-depolarizing muscle relaxants if neuromuscular blockade is required 4, 5

Monitoring Requirements

Continuous intraoperative monitoring must include:

• SpO2 monitoring continuously 1
• Blood or end-tidal carbon dioxide levels whenever possible 1
• Full monitors and safety measures per American Academy of Pediatrics and American Society of Anesthesiologists guidelines 1

Personnel and Setting

Procedures must be performed:

• With an anesthesiologist experienced in DMD management in attendance 1
• In optimal medical settings (postanesthetic care unit or operating room) 1
• With a respiratory therapist skilled in noninvasive positive pressure ventilation (NPPV) 1
• With ICU availability for postprocedure management 1

Emergency Preparedness

Dantrolene must be immediately available wherever general anesthesia is administered, as it is the specific antagonist for both true MH and can be beneficial in MH-like reactions. 1, 2, 3 Initial dosing:

• 2-3 mg/kg initially, then 1 mg/kg every 5 minutes until treatment goals are reached 2
• Continue until end-tidal CO2 is <6 kPa with normal minute ventilation and core temperature is <38.5°C 2

Common Pitfalls to Avoid

Do not assume safety based on previous uneventful anesthetics. 2 Numerous reports document patients receiving several apparently uneventful anesthetics before experiencing their first reaction 2.

Do not delay treatment if an MH-like reaction is suspected. 1, 2 Early recognition and prompt action are essential, as delayed diagnosis is associated with increased mortality and complications 1, 2.

Do not misinterpret early signs such as increased end-tidal CO2 and tachycardia as being due to other causes, as this delays life-saving treatment 2.

Do not use "trigger-free" anesthetic machines without proper preparation. Ensure volatile anesthetics are completely removed from the circuit and fresh gas flow is used to flush the system before use in dystrophic patients 1.