This study investigates the sodium content in the calf muscle and the skin obtained via 23Na-magnetic resonance imaging in patients with chronic adrenal insufficiency compared to healthy controls.

Patients with chronic adrenal insufficiency depend on lifelong glucocorticoid and mineralocorticoid replacement therapy. Monitoring is based on clinical and laboratory parameters reflecting hemodynamic stability, electrolyte status and plasma renin concentration. Reduced subjective well-being is however often described by these patients in absence of clinical or laboratory abnormalities and is thus a strong indicator of the gap between the concept of adequate hormone substitution and patients' requirements. This study investigates the sodium content in the calf muscle and the skin obtained via 23Na-magnetic resonance imaging (MRI) in patients with chronic adrenal insufficiency compared to age-, sex- and BMI- matched healthy controls. The aim of the study is to evaluate the potential role of 23Na-MRI for monitoring of hormone replacement by investigating tissue sodium concentrations in patients with adrenal insufficiency.

Inclusion Criteria:

• Age > 18 years
• Written informed consent
• Chronic adrenal insufficiency (first diagnosis > 6months), stable hormone replacement therapy with glucocorticoids (no dose-adjustment >50mg hydrocortisone within the last 8 weeks) and mineralocorticoids (only primary adrenal insufficiency)! Or healthy control (no adrenal insufficiency, normal serum-electrolytes, normotensive blood pressure, no medication with a known influence on the electrolyte balance)!

Exclusion Criteria:

• Pregnancy or breast-feeding
• Metal-implant (not MRI-compatible)
• Claustrophobia
• Chronic internistic disease (hypertension, heart failure, liver cirrhosis)
• Polydipsia (>4l/d)
• Long-term medication that can cause a hyponatraemia (for example diuretics)