Endocrine Abstracts

Introduction: Idiopathic Isolated Adrenocorticotropic hormone (ACTH) deficiency (IIAD) is a rare cause of secondary adrenal insufficiency. It can present with a variety of clinical symptoms, mainly chronic fatigue and euvolemic hyponatraemia, and may coexist with autoimmune disease, most commonly Hashimoto’s thyroiditis. Radiographically, an empty sella turcica image can be seen. We present 3 cases of isolated ACTH deficiency.

Case 1: A 47-year-old woman was referred for investigation of adrenal insufficiency due to low morning cortisol levels in a laboratory test performed in the context of investigation of hypertension. Hormone lab tests showed morning Cortisol <1μg/dl, ACTH 6.8 pg/ml (NL 7-64). The rest of pituitary axes were intact. Tetracosactrin (250μg) stimulation test showed a maximum cortisol response of 8.56μg/dl. Pituitary on imaging was normal. The patient was set on hydrocortisone replacement therapy while continuing to receive her antihypertensive treatment.

Case 2: A 45-year-old man, with no previous history, had an episode of confusion during febrile diarrheal syndrome. During his hospitalization he also presented episodes of hypoglycemia. The initial hormonal test showed very low basal serum cortisol levels (morning <0.2μg/dl) and ACTH (1 pg/ml), while in the glucagon test there was no cortisol response (maximum value = 0.2μg/dl). The rest of hypothalamic-pituitary axes were intact. Pituitary imaging test was negative. At the same time, the patient was also diagnosed with autoimmune primary hypothyroidism and treated with thyroxine one week after the initiation of hydrocortisone replacement.

Case 3: A 74-year-old man with hyperthyroidism due to Graves’ disease treated with methimazole was hospitalized for fever and hyponatremia (Na = 124). The hormonal tests revealed low levels of cortisol (morning <0.7μg/dl) and ACTH (4 pg/ml), as well as thyrotoxicosis [TSH 0.017, FT4 1.74 (FT 0.80-1.28 mg/dl)]. Corticosteroid deficiency was confirmed by a subsequent stimulation test with 250μg tetracosactrin (maximum cortisol response 5.56μg/dl) and a glucagon test (maximum cortisol response 1μg/dl). The rest of pituitary axes were intact and pituitary MRI showed no anatomical damage. The patient was treated with hydrocortisone.

Conclusion: • The diagnosis of IIAD is often missed and becomes apparent after a triggering event such as fever or thyrotoxicosis.

• The presence of hyponatraemia or hypoglycaemia should raise the suspicion of adrenocortical insufficiency

• The etiology of IIAD remains unclear, although the coexistence of autoimmune thyroid disease is common.