A girl with progressive fatigue and hyponatremia: answer

During the last few months preceding admission, the patient's mother noticed progressive fatigue and weakness as well as a craving for salt. Clinical examination revealed moderate hyperpigmentation, particularly at the elbows, knees, palmar creases and buccal mucosa. The patient’s mother noted that, contrary to previous years, the patient’s suntan had not faded, even by the middle of the fall.

Typical but not specific symptoms and hyperpigmentation suggested the diagnosis of adrenal insufficiency despite a normal plasma K⁺ concentration.

The patient was asked to perform an adrenocorticotropic hormone (ACTH) stimulation test 1 week after admission, when she was clinically and biochemically stable. This test revealed elevated ACTH (result 273 pg/ml, normal range 9–52 pg/ml) and very low cortisol levels (1.0 mg/dl before and 1 h after ACTH administration). The aldosterone level was low (0.8 ng/dl), but the renin level was in the normal range. The test for antibodies to the adrenals was negative. An abdominal ultrasound scan and magnetic resonance imaging revealed no pathology of the adrenals. These results are consistent with a diagnosis of Addison’s disease. The patient was subsequently treated with hydrocortisone (15 mg/m²/day) and fludrocortisone (1 mg/day). She remained stable with normal Na⁺ and K⁺ levels and was discharged with guidelines on stress dose of hydrocortisone in the case of coincidental illness or surgery. She has been closely followed up and remains in good health at 6 months post-diagnosis.