Muscular dystrophies and myotonias
Stem
A 13-year-old boy, 40 kg, with Duchenne muscular dystrophy fell from his wheelchair and needs open reduction and internal fixation of a femoral shaft fracture. He has used a wheelchair for three years and takes daily deflazacort. His echocardiogram six months ago showed an ejection fraction of 45%. He has a large tongue, a weak cough, and no orthopnea. Potassium is normal.
Question
How will you plan and conduct his anesthetic?
Ideal answer
HeadlineThe threat is rhabdomyolysis with hyperkalemic arrest, so no succinylcholine and no volatile: propofol and remifentanil TIVA, while I support a weak heart and weak breathing.
- ECG, echo, respiratory function and a baseline CK. The CK helps if he later develops rhabdomyolysis; stress-dose steroids because he takes deflazacort.1
- No succinylcholine, no volatile, even at induction or unflushed machine. Both have caused hyperkalemic cardiac arrest and rhabdomyolysis in these boys.1,2
- Difficult airway ready; rocuronium only if needed, quantitatively monitored. Macroglossia; onset is delayed and the block prolonged, so a baseline before dosing.1
- Arterial line, slow induction titration, TEE available. His ejection fraction is reduced.1
- Femoral or fascia iliaca catheter; extubate awake, fully reversed. Opioid-sparing analgesia; non-invasive ventilation if his cough is poor, and early mobilization, because prolonged immobilization weakens him further.1
Watch for: hyperkalemia, dark urine and arrhythmias into the postoperative period.
Breaking down the answer
- Succinylcholine is the headline — its boxed warning describes acute rhabdomyolysis with hyperkalemia, ventricular dysrhythmias and death in apparently healthy children later found to have a myopathy, most often Duchenne.2
- Not classic MH — it is anesthesia-induced rhabdomyolysis: the unstable membrane breaks down, so volatiles are avoided entirely, including during machine washout.1 Nondepolarizers are safe.
- The heart decides the hemodynamics — cardiomyopathy and arrhythmias limit tolerance of propofol boluses and fluid shifts.1
- Respiratory reserve — weak cough and restrictive mechanics predict atelectasis; early aggressive weaning is favored.1
- Myotonic dystrophy is a different disease — autosomal dominant, with conduction block, restrictive lungs and aspiration risk; it is not MH-susceptible but carries its own drug traps.3
Follow-up question
Forty minutes into the case, you learn that the anesthesia machine had been used for a sevoflurane case and was not flushed. His heart rate climbs to 145, the T waves peak, the QRS widens, and the potassium returns at 7.4. What do you do?
Follow-up answer
HeadlineHyperkalemia from rhabdomyolysis triggered by volatile exposure; I say so to the room and call for help.
I remove the source: a clean circuit, or a bag with high-flow oxygen from a fresh source, and continue propofol. Intravenous calcium to stabilize the membrane, insulin with dextrose and bicarbonate to shift potassium, hyperventilation, and ACLS if he loses his pulse. CK, myoglobin, a blood gas and repeated potassium; urine output kept high. If he becomes rigid or hyperthermic with a rising CO2, dantrolene, because I cannot exclude MH in the moment. Potassium and rhythm every 10–15 minutes, then the ICU.
Pitfalls that cost points
- Calling Duchenne "MH-susceptible" and stopping there, instead of naming rhabdomyolysis and hyperkalemia.
- Reversing a myotonic patient with neostigmine, which can worsen myotonia.3
- Letting a myotonic patient get cold and shiver.3
Rapid-fire
Q: What happens if you give succinylcholine in myotonic dystrophy? A: Exaggerated contracture, masseter spasm, laryngospasm, or severe hyperkalemia.3
Q: What triggers myotonia under anesthesia? A: Hypothermia, shivering, succinylcholine, and electrical or mechanical stimulation; I keep him warm and deep enough to stay still.3
Q: What cardiac problem threatens a myotonic patient? A: Conduction disease up to complete heart block, so pacing must be ready.3
Q: Is regional anesthesia safe in Duchenne? A: Yes; spinal, epidural and caudal techniques have been reported without complications.1
Q: How do myotonic patients respond to sedatives and opioids? A: They are hypersensitive to respiratory depression and may emerge slowly, so I reduce doses and use multimodal analgesia.3
Numbers to know
| Item | Value |
|---|---|
| Myotonic dystrophy type 1 | About 1 in 8000; ~98% of cases3 |
| Mitral valve prolapse in type 1 | About 20%3 |
| Duchenne relaxants | Delayed onset, prolonged duration1 |
| Succinylcholine in Duchenne | Avoid (boxed warning)2 |
Links
- succinylcholine, Malignant hyperthermia, hyperkalemia, Heart failure and reduced ejection fraction, Scoliosis surgery
- OrphanAnesthesia recommendations for Duchenne muscular dystrophy; FDA succinylcholine boxed warning
Sources
- 1.Anaesthesia recommendations for patients suffering from Duchenne muscular dystrophy · OrphanAnesthesia (Anästh Intensivmed), 2014 · ai-online.info
- 2.QUELICIN (succinylcholine chloride) injection prescribing information · FDA / DailyMed · dailymed.nlm.nih.govBoxed warning: hyperkalemic rhabdomyolysis in children with undiagnosed myopathy, most often Duchenne.
- 3.Myotonic dystrophy · OpenAnesthesia (IARS), 2023 · openanesthesia.org
Facts on this page were checked against these sources on Oct 15, 2026. Guidelines change; confirm doses against current institutional protocols.