Endocrine Abstracts

Adrenal insufficiency is serious, life-threatening condition. Classical features include nausea, malaise, weight loss and hypotension. It is usually diagnosed at a late stage only when it presents as adrenal crisis. We report a patient with autoimmune adrenal insufficiency who presented with chronic hyponatremia and a repeatedly normal serum cortisol level. A 66-year-old female was referred to endocrinology with a 12-month history of hyponatraemia (Na 125–131 mmol/l). She was feeling tired and sometimes dizzy. There was no weight loss. She was not taking any steroid or opioid therapy. On examination, she was euvolemic with no postural hypotension. Other systemic examination was normal. Investigations showed Na 125 mmol/l, K 4.3 mmol/l, with normal renal function, serum osmolality: 265 mmol/kg, urinary osmolality 375 mmol/kg, urinary sodium: 50 mmol/l, TSH: 1.51 mU/l, 0900 h cortisol 378 nmol/l (RR: 185–624 nmol/l). CT head and CT chest, abdomen and pelvis were normal. She was diagnosed with Idiopathic SIADH; she was treated with fluid restriction and briefly with demeclocycline. She travelled to Australia on holiday, where she was admitted for a saline infusion. A year later she re-presented with hyponatraemia. Further investigation showed Na 122 mmol/l, 0900 h cortisol 312 nmol/l, with no significant response in a short Synacthen test (basal cortisol 237 nmol/l, 30 min 245 nmol/l and 60 min 242 nmol/l), with ACTH 612 ng/l (RR: <50 ng/l), indicating adrenal insufficiency. Adrenal antibodies were detected. Addison’s disease was diagnosed. She was treated with hydrocortisone and fludrocortisone. She felt much better after starting treatment; the sodium level rose to 142 mmol/l after treatment. This patient demonstrates that adrenal insufficiency may occur as a chronic condition, with hyponatremia and malaise but without weight loss or hypotension, and with no progression or crisis. ACTH responsiveness was significantly impaired without any change in the basal cortisol level. Clinicians should not rely on a normal basal cortisol level for excluding adrenal insufficiency in hyponatraemia, but should also consider the ACTH level or a short Synacthen test. It is not clear why autoimmune disease should damage ACTH-responsiveness before it affects basal cortisol secretion; a similar finding has been made in the context of adrenal metastasis.