Rapid Quantitative Assessment of Muscle Sodium Dynamics After Exercise Using 23Na‐MRI in Dysferlinopathy and Healthy Controls

Abstract

ABSTRACT Background Dysferlin plays a key role in cell membrane repair; its absence or malfunction in patients with dysferlin‐deficient limb girdle muscular dystrophy leads to muscle fibre death. Muscle magnetic resonance (MR) imaging allows non‐invasive and repeatable measurements that can report on pathological changes observed in dysferlinopathy patients (DP). We aimed to demonstrate the feasibility of utilising volume‐localised 23Na spectroscopy as a novel approach to characterise muscle Na+ content and biexponential T2* at rest, and dynamically post‐exercise, in patients with dysferlinopathy and in matched healthy controls. Methods Adult DP and age and sex matched healthy volunteers (HV) were recruited and scanned on a 3 T clinical MR scanner. Following baseline scans, participants performed physiotherapist‐guided isometric dorsiflexion contractions until tibialis anterior (TA) muscle exhaustion. Dynamic volume‐localised sodium‐23 (23Na)‐ and proton (1H)‐MR scans were acquired serially for 35 min post‐exercise. MR data were analysed to determine TA lipid content, change in TA sodium content, biexponential sodium T2* properties and TA water 1H T2. Results Ten DP (mean age ± standard deviation [SD]: 38.0 ± 10.8 years; 80% female) and 10 HV (mean age ± SD: 38.9 ± 11.5 years) were scanned. Baseline muscle water 1H T2 and sodium concentration were significantly higher in DP compared to matched controls (1H T2 DP [SD] = 33.8 [2.7] ms, 1H T2 HV = 29.3 [1.1] ms, p < 0.001; [23Na]DP = 36.2 [11.4] mM, [23Na]HV = 19.6 [3.1] mM, p < 0.001). 1H T2 and sodium content in healthy controls showed significant post‐exercise elevation with a slower time‐to‐peak for sodium content compared to 1H T2. 1H T2 and sodium content change post‐exercise was highly variable in the DP group. Notably, 23Na dynamics in one DP with normal muscle fat fraction were similar to HV. Biexponential 23Na T2* was measured at baseline in HV (T2*slow = 13.4 [2.3] ms, T2*fast = 2.2 [1.3] ms), and DP (T2*slow = 14.0 [1.5] ms and T2*fast = 1.0 [0.5] m). Equivalent measurements post‐exercise revealed an increase in the fraction of the slow‐relaxing component in HV (p < 0.05), consistent with oedematous changes. Conclusions Assessment of TA muscle fat fraction, 1H T2, sodium content and sodium T2* relaxation properties revealed differences at baseline and in post‐exercise dynamics between patients with dysferlinopathy and matched controls. Post‐exercise 23Na recovery dynamics followed a well‐defined time course in HV. Heterogeneous alterations in sodium content and MR relaxation properties in DP may reflect altered ion homeostasis associated with chronic muscle damage.

Keywords

• biomarkers
• dysferlinopathy
• imaging
• muscle MRI
• muscular dystrophy
• sodium MRI