Use of magnetic resonance imaging and 31p-spectroscopy to explore muscle energetics in fibromyalgia patients

Background: Fibromyalgia (FM) is defined as a chronic syndrome characterized by diffuse pain. FM patients generally complain of muscle fatigue during physical activities and symptoms worsening after exercise. Some studies have explored muscle performances in FM patients. Similarly, we reported that all variables of muscle performances were decreased in FM patients as compared to the controls [1]. We found that muscle impairment predominated over aerobic processes. The 31P nuclear magnetic resonance spectroscopy (NMRS) appears especially useful to study muscle energy metabolism because it is non-invasive and allows the exploration during exercise.
Objectives: The purposes were: (1) to determine the maximal transverse section (MTS) of calf muscles by Magnetic Resonance Imaging (MRI) in order to calculate the individual mechanical loads of exercise without requiring the measurement of the maximal voluntary torque; (2) to monitor, by 31P-NMRS, high-energy phosphate metabolism and intracellular pH at rest, during exercise and recovery periods by means of continuous spectra acquisitions with an adequate temporal resolution; (3) to determine an original efficacy muscular index with the help of the ergometric and spectroscopic parameters; (4) to explore the oxidative pathway by means of determination of the PCr rephosphorylation time constant.
Methods: Eight women with fibromyalgia (FM) and 30 healthy volunteers were included in this study. MRI of the dominant leg was acquired in order to determine the MTS of calf muscles and thus to calculate the different loads of exercise (dynamic plantar flexions). Subjects performed 3-6 bouts of 2 minutes with workload increments until exhaustion. Spectra were acquired continuously at rest, during the exercise and recovery periods. The analysis concerned the gamma-, alpha- and beta- ATP, Pi, PCr peaks, and intracellular pH. At the end of the exercise, the muscular efficacy index and the PCr re-phosphorylation time constant were calculated.
Results: The MTS of the ankle plantar flexors reached respectively 43 cm² and 36.7 cm² in the control and FM groups (p > 0.05). No significant difference (p > 0.05) was observed between both groups in spectroscopic data registered at rest [10.7 (control) vs 9.1 (FM) for PCr/Pi rest ; 7.01 (control) vs 6.99 (FM) for pHrest] and at the end of exercise [1.18 (control) vs 0.68 (FM) for PCr/Pi end ; 6.89 (control) vs 6.81 (FM) for pHend]. However, the muscular efficacy index was significantly reduced in FM patients (1.25) in comparison with control group (2.46) (p < 0.05). Two patients presented an index extremely low (0.3 and 0.4). The PCr time constant was not different between control subjects (27.7 s) and FM patients (25.6 s) (p > 0.05).
Conclusion: Our original protocol, not based on maximum voluntary contraction assessment, did not indicate any abnormalities in glycolytic and oxydative pathways in FM patients. We demonstrated a low efficiency of chemical to mechanical energy shift in FM patients. These results suggested a deconditioning syndrome without primitive muscular abnormalities in FM patients and displayed the importance of aerobic muscular rehabilitation.
References: [1]Maquet D, Croisier JL, Renard C, Crielaard JM. Muscle performance in patients with fibromyalgia. J Bone Spine. 2002;69:293-9.