Caffeine impairs intramuscular energy balance in patients susceptible to malignant hyperthermia

Malignant hyperthermia (MH) is a metabolic myopathy with an abnormal release of calcium by the sarcoplasmic reticulum (SR), triggered by volatile anesthetics and succinylcholine. Similarly, caffeine enhances Ca2+ release by the SR in vitro. In a prospective, randomized study, high-energy phosphates were studied by intramuscular 31-phosphorus magnetic resonance spectroscopy (P-31-MRS) in 10 MH-susceptible (MHS) and 7 MH-nonsusceptible (MHN) subjects before and after injection of 0.5 ml caffeine (20 mM). Intramuscular energy balance, measured by the ratios of P-i/PCr and P-i/(gamma)-ATP, did not differ between MHS and MHN patients before and after intramuscular caffeine injection. However, within each group, P-i/PCr and P-i/(gamma)-ATP increased significantly only in the MHS group. Intramuscular caffeine injection seemed to impair the metabolic balance in MHS individuals. This may reflect a local calcium overload leading to consumption of high-energy phosphates and increase of inorganic phosphate. Intramuscular stimulation by caffeine and P-31-MRS may provide a valuable tool to investigate MH-related metabolic disturbances.