A 32-year-old male patient develops sudden onset muscle rigidity, tachycardia (HR 140/min), and core temperature rise to 39.2°C during general anesthesia with succinylcholine and sevoflurane. Anesthesia is immediately discontinued. Which investigation is most appropriate to confirm the diagnosis of malignant hyperthermia at this stage?

Explanation

## Investigation of Choice for Confirming Malignant Hyperthermia ### The Caffeine Halothane Contracture Test (CHCT) **Key Point:** The muscle biopsy with CHCT remains the gold-standard diagnostic test for malignant hyperthermia susceptibility. It is the most specific and sensitive confirmatory investigation. **High-Yield:** CHCT involves: 1. Obtaining a fresh muscle biopsy (typically from vastus lateralis) 2. Exposing isolated muscle strips to caffeine and halothane 3. Measuring contracture response — abnormal contracture in MHS (malignant hyperthermia susceptible) patients 4. Sensitivity and specificity both >99% when properly performed ### Why CHCT is the Gold Standard | Aspect | CHCT | Genetic Testing | CK/Myoglobin | ABG/Electrolytes | |--------|------|-----------------|--------------|------------------| | **Timing** | Can be done acutely or within weeks | Weeks to months | Acute (supportive only) | Acute (supportive only) | | **Diagnostic** | Confirms MH susceptibility | Identifies mutation (not all MH patients have known mutations) | Reflects muscle damage, not MH | Reflects acute complications, not MH | | **Gold Standard** | YES | Emerging, not yet standard | No | No | | **Specificity** | >99% | High but incomplete gene coverage | Non-specific | Non-specific | **Clinical Pearl:** While genetic testing is increasingly used and can be done in parallel, it is NOT yet the standard confirmatory test because: - Not all MH-susceptible individuals carry identified RYR1 or CACNA1S mutations - Negative genetic test does not exclude MH susceptibility - CHCT remains the reference standard for definitive diagnosis **Mnemonic: CHCT Gold Standard — Caffeine Halothane Contracture Test** - **C** — Confirmatory (gold standard) - **H** — Halothane exposure on muscle - **C** — Contracture response measured - **T** — Test of susceptibility ### Acute Management vs. Diagnostic Confirmation **Important Distinction:** - **During acute episode:** Treat with dantrolene, supportive care, ABG, CK, myoglobin, electrolytes (options 3 and 4 are acute management tools) - **After stabilization:** Perform CHCT to confirm MH susceptibility for future anesthetic planning **Warning:** Do NOT delay dantrolene administration while awaiting confirmatory tests. CHCT is done AFTER the acute crisis is managed, typically within 2–4 weeks.