Two Hurt More Than One: Severe Hyponatraemia and Rhabdomyolysis as Presenting Features of Addison’s Disease

Addison's disease (AD) is characterized by non-specific symptoms and electrolyte disorders, namely hyponatraemia and hyperkalaemia; rhabdomyolysis is uncommon. AD may manifest at onset with a life-threatening adrenal crisis which is triggered by stressful events. We describe the case of a young man who was hospitalized for severe myalgia and fatigue. Severe hypotonic hyponatraemia, rhabdomyolysis and hypotension were found; hormonal assessment unexpectedly revealed primary adrenal insufficiency. Saline infusion and intravenous hydrocortisone significantly improved the patient's condition and normalized sodium and muscle enzyme levels; thereafter, he was switched to oral steroid therapy. The autoimmune origin of AD was ascertained by the positivity of adrenal cortex autoantibodies and 21b-hydroxylase autoantibodies. The association of hyponatraemia and rhabdomyolysis may be the initial finding of an as yet unknown AD, which requires proper investigation and treatment.