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 (31P‐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 Pi/PCr and Pi/γ‐ATP, did not differ between MHS and MHN patients before and after intramuscular caffeine injection. However, within each group, Pi/PCr and Pi/γ‐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 31P‐MRS may provide a valuable tool to investigate MH‐related metabolic disturbances. Muscle Nerve 28: 353–358, 2003