A 38-year-old woman presents with progressive fatigue, weight loss, and hyperpigmentation over 3 months. Examination reveals darkening of skin creases and mucous membranes. Laboratory investigations show: Na⁺ 128 mEq/L, K⁺ 5.8 mEq/L, fasting glucose 72 mg/dL, and morning cortisol 3 μg/dL (normal: 10–20 μg/dL). ACTH level is 420 pg/mL (normal: 10–50 pg/mL). What is the most appropriate next step in management?

Explanation

## Clinical Diagnosis and Rationale This patient presents with **primary adrenal insufficiency (Addison's disease)** based on: - Classic triad: hyperpigmentation (elevated ACTH stimulating melanocytes), electrolyte abnormalities (hyponatremia Na⁺ 128, hyperkalemia K⁺ 5.8), and hypoglycemia (fasting glucose 72 mg/dL) - Low morning cortisol (3 μg/dL; normal 10–20) with markedly elevated ACTH (420 pg/mL; normal 10–50) confirms **primary** adrenal failure - The high ACTH reflects loss of negative feedback due to cortisol deficiency ## Why Immediate Hydrocortisone Replacement Is the Next Step **Key Point:** In a biochemically confirmed case of primary adrenal insufficiency, the **most appropriate next step is to start hydrocortisone replacement immediately and refer to endocrinology** — not to delay treatment for imaging. Untreated adrenal insufficiency can rapidly progress to an Addisonian crisis (cardiovascular collapse, shock, death). **High-Yield (Harrison's Principles of Internal Medicine, 21st ed.):** Once the diagnosis of primary adrenal insufficiency is established biochemically (low cortisol + high ACTH), treatment must not be delayed. The standard of care is: 1. **Hydrocortisone** 15–25 mg/day in divided doses (or stress-dose hydrocortisone 100 mg IV if in crisis) 2. **Fludrocortisone** for mineralocorticoid replacement (to address hyponatremia and hyperkalemia) 3. Referral to endocrinology for etiological workup (CT abdomen, autoimmune antibodies, TB workup) as an **outpatient or concurrent** step — not as the immediate priority **Clinical Pearl:** CT abdomen is important for identifying the underlying cause (TB, autoimmune, malignancy) but is an **investigative/etiological** step, not the immediate management priority. In a stable patient, imaging can be arranged concurrently or shortly after initiating replacement therapy. Delaying treatment to obtain imaging first risks precipitating an adrenal crisis. ## Why Other Options Are Incorrect - **Option A (CT abdomen):** Useful for etiology but NOT the most appropriate *next* step — treatment takes priority over imaging in confirmed adrenal insufficiency. - **Option B (Plasma renin/aldosterone):** May be useful to confirm mineralocorticoid deficiency but is not the immediate next step when the diagnosis is already clear. - **Option D (High-dose dexamethasone suppression test):** This test is used to evaluate **Cushing's syndrome** (cortisol excess), not adrenal insufficiency. It is entirely inappropriate here. ## Management Algorithm | Priority | Action | |----------|--------| | **Immediate** | Start hydrocortisone replacement; refer to endocrinology | | **Concurrent/Soon** | Add fludrocortisone for mineralocorticoid deficiency | | **Etiological workup** | CT abdomen, anti-adrenal antibodies, TB workup | **Reference:** Harrison's Principles of Internal Medicine, 21st ed., Chapter on Adrenal Insufficiency; KD Tripathi Essentials of Medical Pharmacology, 8th ed.