Endocrine Abstracts

Introduction: We report a patient with hypokalaemia secondary to Cushing’s syndrome (CS) to reinforce this commonly forgotten association.

Case report: A 57 years old lady with newly diagnosed hypertension, hyperlipidaemia and diabetes mellitus presented with persistent hypokalaemia for evaluation. She had tinea corporis but otherwise did not look Cushingoid. Investigations: K 2.6 (RI: 3.50–5 mmol/l), HCO₃ 35 (RI: 19–31 mmol/l), Urine K/Cr 8.1. Both renin and aldosterone were suppressed. 24 h urinary free cortisol (UFC) was elevated at 1811 (RI: 59–413 nmol/day); 0800 h cortisol after 1 mg overnight dexamethasone suppression test (DST) was elevated at 1156 nmol/l. The patient denied taking any liquorice or corticosteroids. ACTH dependent CS was made with ACTH level of 12.1 pmol/l. Overnight 8 mg DST suppressed the cortisol to more than 50% (1223 nmol/l→ 351 nmol/l). Brain imaging revealed a lytic lesion epicentered in the body of the sphenoid bone, involving the sella and clivus, suspicious for a chordoma. BIPSS was not performed as interpretation may be difficult given the proximity of the lesion to the pituitary. Spironolactone was started to block the mineralocorticoid (MC) effect of cortisol and she was promptly referred to neurosurgery.

Discussion: Activation of MC receptors by cortisol is normally limited due to its conversion to inactive cortisone at the sites of aldosterone action by the enzyme 11-β-hydroxysteroid dehydrogenase type 2 (11-β-HSD2). In ACTH-dependent CS, cortisol secretion exceeds the metabolic capacity of 11-β-HSD2. ACTH inhibits 11-β-HSD2 and there may also be hypersecretion of nonaldosterone mineralocorticoids such as deoxycorticosterone (DOC) and corticosterone. Excess MC activity leads to sodium retention, hypertension, hypokalaemia, metabolic alkalosis, low plasma aldosterone and renin activity. Besides CS, other differentials to consider include 11-β-HSD2 deficiency, liquorice ingestion, Liddle’s syndrome, DOC-secreting tumour and certain forms of congenital adrenal hyperplasia.

Conclusion: CS presents with hypokalaemia. Earlier diagnosis and management may improve outcome.