Delayed Emergence of Isolated Secondary Adrenal Insufficiency: A Case Report

Secondary adrenal insufficiency (SAI) is a rare condition caused by adrenocorticotropic hormone (ACTH) deficiency, which disrupts ACTH secretion by the pituitary gland and can lead to chronic hyponatremia. However, idiopathic delayed onset of isolated adrenal insufficiency without triggering factors is an unusual finding and poses a challenging diagnosis. We present the case of an 80-year-old woman with hypothyroidism, hypertension, previous tobacco use, and squamous cell carcinoma of the ankle who presented with weakness and fatigue. Blood work showed hyponatremia (126 mmol/L), nonfasting blood glucose of 139 mg/dL, and elevated erythrocyte sedimentation rate (ESR, 83 mm/hr). Initial treatment included urea administration and water restriction. Initial imagining included a CT of the chest which revealed mediastinal lymphadenopathy, leading to suspicion of the syndrome of inappropriate antidiuretic hormone (SIADH) from malignancy. Despite increasing urea and adding NaHCO₃, sodium levels dropped further. Tolvaptan was administered but showed no improvement. Endocrinology recommended hydrocortisone sodium succinate (Solu-Cortef) leading to sodium normalization and symptom resolution. A full pituitary workup revealed low dehydroepiandrosterone sulfate (DHEA-S), and abdominal CT showed atrophic adrenal glands. MRI of the sella turcica was normal with no evidence of a mass. The patient was discharged on an oral course of Solu-Cortef with stable sodium levels (139 mEq/L). This is among the first reported cases of unprovoked isolated adrenal insufficiency with abnormal cortisol, ACTH, DHEA-S levels, and normal renin and aldosterone levels. Diagnosis is often delayed due to nonspecific symptoms. Once identified, corticosteroid replacement therapy is the gold standard for management.