A 28-year-old female with a family history of malignant hyperthermia (her father had an MH crisis during surgery) is scheduled for elective laparoscopic cholecystectomy. She is asymptomatic and has never undergone general anesthesia. Which investigation is most appropriate to determine her MH susceptibility status before surgery?

Explanation

## Preoperative Investigation for MH Susceptibility Screening ### Clinical Context: Asymptomatic Family History **Key Point:** In a patient with a positive family history of MH but no prior anesthetic exposure, muscle biopsy with CHCT is the most appropriate definitive investigation to determine MH susceptibility before elective surgery. **High-Yield:** CHCT is indicated when: 1. Positive family history of MH 2. Patient is asymptomatic (no clinical signs at rest) 3. Definitive diagnosis needed for future anesthetic planning 4. Patient is a candidate for muscle biopsy (no contraindications) ### Why CHCT Over Other Options in This Scenario | Investigation | Role in Preoperative Screening | Utility in This Case | |---------------|--------------------------------|----------------------| | **CHCT** | Gold standard for MH susceptibility | YES — definitive diagnosis before surgery | | **Genetic testing** | Emerging; identifies mutations | Partial — negative test does not exclude MH | | **Baseline CK** | Screening tool (weak); elevated in some MHS | Weak — non-specific, may be normal in MHS | | **Core temperature** | Not diagnostic | No — resting temperature is normal in MHS | **Clinical Pearl:** The distinction between preoperative screening and acute diagnosis: - **Preoperative:** CHCT is the definitive test to guide anesthetic technique (avoid triggering agents) - **Acute MH crisis:** CK, myoglobin, ABG, electrolytes guide acute management; CHCT done later for confirmation ### Genetic Testing: Why Not First-Line in Preoperative Screening? **Warning:** Genetic testing has limitations in preoperative screening: - **Incomplete penetrance:** Not all carriers of RYR1/CACNA1S mutations are MH-susceptible - **Incomplete gene coverage:** 15–20% of MH-susceptible patients have no identified mutation - **Negative test does not exclude MH:** A negative genetic test cannot safely exclude MH susceptibility - **Positive test requires confirmation:** Even a positive mutation requires CHCT for functional confirmation **Mnemonic: CHCT Preoperative — Confirmatory, Helps plan, Contracture test, True gold standard** ### Anesthetic Management Based on CHCT Result ```mermaid flowchart TD A[Preoperative MH Screening]:::outcome --> B[CHCT Performed]:::action B --> C{CHCT Result?}:::decision C -->|MHS Positive| D[Avoid triggering agents]:::action C -->|MHS Negative| E[Standard anesthesia safe]:::action D --> F[Use TIVA + non-depolarizing agents]:::action D --> G[Have dantrolene available]:::action E --> H[Routine GA with any agent]:::action ``` **Clinical Pearl:** If CHCT is positive, anesthesia plan changes to: - Total intravenous anesthesia (TIVA) with propofol - Non-depolarizing neuromuscular blockers (avoid succinylcholine) - Dantrolene readily available - Increased monitoring (core temperature, CK, myoglobin post-op)