Primary hyperaldosteronism induces congruent alterations of sodium homeostasis in different skeletal muscles: a 23Na-MRI study

Abstract

Background: Sodium homeostasis is disrupted in many cardiovascular diseases, which makes non-invasive sodium storage assessment desirable. In this regard, sodium MRI has shown its potential to reveal differences in sodium content between healthy and diseased tissues as well as treatment-related changes of sodium content. When different tissues are affected disparately, simultaneous assessment of these compartments is expected to provide better information about sodium distribution, reduce examination time, and improve clinical efficiency.

Objectives: The objectives were (1) to investigate sodium storage levels in calf and pectoral muscle in healthy controls and patients and quantify changes following medical treatment and (2) to demonstrate homogeneous disruption in skeletal muscle sodium storage in patients with primary hyperaldosteronism (PHA).

Methods: We assessed sodium storage levels (relative sodium signal intensity, rSSI) in the calf and pectoral muscles of eight patients with PHA prior and after treatment and 12 age- and sex-matched healthy volunteers.

Results: Calf and pectoral muscle compartments exhibited similar sodium content both in healthy subjects (calf vs pectoral rSSI: 0.14 ± 0.01 vs 0.14 ± 0.03) and PHA patients (calf vs pectoral rSSI: 0.19 ± 0.03 vs 0.18 ± 0.03). Further, we observed similar treatment-related changes in pectoral and calf muscles in the patients (proportional rSSI change calf: 26%; pectoral: 28%).

Conclusion: We found that sodium was distributed uniformly and behaved equally in different skeletal muscles in Conn's syndrome. This allows to measure both heart and skeletal muscle sodium signals simultaneously by a single measurement without repositioning the patient. This increases 23Na-MRI's clinical feasibility as an innovative technique to monitor sodium storage.

Figure 1

Exemplary ROI placement in the pectoral muscle (A and B) and in the calf (C). The colored overlay in (B) visualizes the parts of the FOV that were used for sodium quantification. In the calf, two ROIs (ROI near (N), ROI far (F)) were averaged to determine rSSI values (C). FOV, field of view; ROI, region of interest; rSSI, relative sodium signal intensity.

Figure 2

The experimental setup for the calf as well as the reference vials below the coil are shown (A). The vial on the left contained 100 mmol/L of NaCl and was used to calculate the rSSI maps. The same setup was used for the chest, with the patients in prone position. (B) and (C) provide a comparison of the calf muscles of a HC and a PHA patient prior treatment, whereas (D) and (E) demonstrate exemplary images of the pectoral muscle and the heart, correspondingly. HC, healthy controls; PHA, primary hyperaldosteronism; rSSI, relative sodium signal intensity.

Figure 3

(A) rSSI values of the pectoral and calf muscle for each individual are plotted (Spearman’s rho 0.63; P  = 0.001). Of note, two HC had the same pair of values, thus only 11 HC are visible. (B) Bland–Altman plot of rSSI measurements comparing calf and pectoralis major showing excellent agreement. (C) Intra-individual changes in pectoralis major and calf rSSIs following PHA-directed treatment. Each patient is represented by one color. Solid line represents the pectoral muscle, the corresponding dashed line the calf muscle of a respective patient. HC, healthy controls; PHA, primary hyperaldosteronism; rSSI, relative sodium signal intensity.