Evaluation of skeletal muscle during calf exercise by 31-phosphorus magnetic resonance spectroscopy in patients on statin medications

Abstract

Muscle pain is a common side effect of statin medications, but the cause is poorly understood. We characterized phosphocreatine (PCr) exercise recovery kinetics in 10 patients with hypercholesterolemia before and after a 4-week regimen of statin therapy using 31-phosphorus magnetic resonance spectroscopy ((31) P-MRS). (31) P spectra were obtained before, during, and after exercise on a calf flexion pedal ergometer. Creatine kinase (CK) serum levels were drawn before and after statin therapy. The mean metabolic recovery time constant in subjects increased from 28.1 s (SE = 6.5 s) to 55.4 s (SE = 7.4 s) after statin therapy. The unweighted mean of the pre/post-recovery time difference was -27.3 s (SE = 12.4 s; P = 0.02). Pre- and post-therapy CK levels were not significantly different (P = 0.50). Metabolic recovery time in the calf is prolonged in patients after statin use. This suggests that statins impair mitochondrial oxidative function, and (31) P MRS is a potential study model for statin-associated myopathy.

Copyright © 2010 Wiley Periodicals, Inc.

Figures

Figure 1

Photograph of a subject using the custom-built MRI-compatible pedal ankle ergometer during 31P-MRS acquisition.

Figure 2

Graph showing the variability in the amounts of phosphocreatine (PCr) and inorganic phosphate (Pi) during the rest, exercise, and recovery phases of calf exercise as measured by 31P MR spectroscopy in a 44 year old white man prior to statin therapy.

Figure 3

Graph comparing the fitted cumulative PCr metabolic recovery time constant in 10 subjects before and after statin therapy. There is a prolonged and blunted cumulative recovery curve following 4 weeks of statin therapy when compared to baseline.