Histology · Year 1 · from Histology
Case 3: Malignant Hyperthermia
Clinical Image
Source: Wikipedia - Malignant Hyperthermia - CC BY-SA 4.0
Case Presentation
A 28-year-old man undergoes general anesthesia for appendectomy. Twenty minutes after induction with sevoflurane (a volatile anesthetic), the anesthesiologist notes rising end-tidal CO2, tachycardia (HR 130), and masseter muscle rigidity. His temperature rapidly rises from 37C to 40C. Arterial blood gas shows pH 7.15 with elevated pCO2 and lactate. A diagnosis of malignant hyperthermia is immediately suspected. The volatile anesthetic is discontinued, 100% oxygen is administered, and dantrolene (a ryanodine receptor antagonist that blocks calcium release from the sarcoplasmic reticulum) is given intravenously. Active cooling measures are initiated. His temperature stabilizes and muscle rigidity resolves. He recovers fully. Subsequent genetic testing confirms a mutation in the RYR1 gene encoding the ryanodine receptor. His family members are counseled to undergo genetic testing before any surgery.
Key Learning Points
- Malignant hyperthermia results from mutations in the ryanodine receptor (RyR1), the calcium release channel in the sarcoplasmic reticulum
- Triggering agents (volatile anesthetics, succinylcholine) cause the mutant channel to open abnormally, releasing massive amounts of calcium
- Uncontrolled calcium release causes sustained muscle contraction (rigidity), generating enormous heat and depleting ATP
- Understanding the normal triad structure (T-tubule, terminal cisternae, RyR1) and excitation-contraction coupling explains this hypermetabolic crisis
- Dantrolene directly blocks RyR1, stopping calcium release and allowing the muscle to relax
Summary: Skeletal Muscle Disorders
These cases illustrate how understanding normal skeletal muscle structure and function is essential for understanding disease:
| Disorder | Structure Affected | Pathophysiology | Clinical Presentation |
|---|---|---|---|
| Duchenne MD | Dystrophin (sarcolemma-ECM link) | Membrane damage during contraction, muscle necrosis | Progressive weakness, pseudohypertrophy, elevated CK |
| Myasthenia Gravis | Acetylcholine receptors (NMJ) | Autoantibodies reduce receptor number, EPP fails to reach threshold | Fatigable weakness, ptosis, diplopia, improves with rest |
| Malignant Hyperthermia | Ryanodine receptor (SR) | Uncontrolled Ca2+ release, sustained contraction | Hyperthermia, rigidity, hypermetabolism during anesthesia |
Each condition affects a specific component of the muscle contraction apparatus, and understanding normal histology and physiology is essential for diagnosis and treatment.