Muscle sodium content in patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Abstract

BACKGROUND: Muscle fatigue and pain are key symptoms of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). Although the pathophysiology  is not yet fully understood, there is ample evidence for hypoperfusion which may  result in electrolyte imbalance and sodium overload in muscles. Therefore, the  aim of this study was to assess levels of sodium content in muscles of patients  with ME/CFS and to compare these to healthy controls. METHODS: Six female  patients with ME/CFS and six age, BMI and sex matched controls underwent  (23)Na-MRI of the left lower leg using a clinical 3T MR scanner before and after  3 min of plantar flexion exercise. Sodium reference phantoms with solutions of  10, 20, 30 and 40 mmol/L NaCl were used for quantification. Muscle sodium content  over 40 min was measured using a dedicated plugin in the open-source DICOM viewer  Horos. Handgrip strength was measured and correlated with sodium content.  RESULTS: Baseline tissue sodium content was higher in all 5 lower leg muscle  compartments in ME/CFS compared to controls. Within the anterior extensor muscle  compartment, the highest difference in baseline muscle sodium content between  ME/CFS and controls was found (mean ± SD; 12.20 ± 1.66 mM in ME/CFS versus  9.38 ± 0.71 mM in controls, p = 0.0034). Directly after exercise, tissue sodium  content increased in gastrocnemius and triceps surae muscles with + 30% in ME/CFS  (p = 0.0005) and + 24% in controls (p = 0.0007) in the medial gastrocnemius  muscle but not in the extensor muscles which were not exercised. Compared to  baseline, the increase of sodium content in medial gastrocnemius muscle was  stronger in ME/CFS than in controls with + 30% versus + 17% to baseline at 12 min  (p = 0.0326) and + 29% versus + 16% to baseline at 15 min (p = 0.0265). Patients  had reduced average handgrip strength which was associated with increased average  muscle tissue sodium content (p = 0.0319, R(2) = 0.3832). CONCLUSION: Muscle  sodium content before and after exercise was higher in ME/CFS than in healthy  controls. Furthermore, our findings indicate an inverse correlation between  muscle sodium content and handgrip strength. These findings provide evidence that  sodium overload may play a role in the pathophysiology of ME/CFS and may allow  for potential therapeutic targeting.