A 57-year-old male was admitted with one-week of nausea and diarrhoea, while continuing his digoxin for atrial fibrillation. He was bradycardic, hypotensive, and had a widespread hyperpigmented rash involving the buccal mucosa, limbs, and torso.

Initial laboratory investigations were significant for hyponatremia (sodium 121 mmol/L), hyperkalemia (potassium 6.6 mmol/L), and a significant acute kidney injury. He was admitted to the intensive care unit for vasopressors and urgent dialysis, with an initial diagnosis of digoxin toxicity.

An early morning cortisol was requested for increasing vasopressor requirements, which returned low at 46 nmol/L. On commencement of stress dose hydrocortisone, vasopressor requirements diminished. The patient initially denied consumption of exogenous steroids and over-the-counter supplements. A punch-biopsy of the hyperpigmented lesion on the upper limb showed cutaneous hyperpigmentation thought secondary to Addison’s disease, given the clinical context. However, an ACTH later returned suppressed at 1 pmol/L, and the patient had normal serum aldosterone (438 pmol/L) and renin levels (34 mu/L). Adrenal antibodies also returned negative at <40.

A further three patients have also presented with unexplained, isolated adrenal insufficiency, over a two-year period- i) a 67-year-old female with severe, symptomatic hyponatremia (sodium 109 mmol/L); ii) a 61-year-old male with fatigue, early morning cortisol of 19 nmol/L, but paradoxically Cushingoid-appearing; and iii) a 67-year-old female with weight gain, deterioration in hypertension and glycaemic control, with a morning cortisol of 3.0 nmol/L.

A unifying diagnosis in this case series has been made and will be presented as an important diagnosis for Endocrinologists to be aware of.