Endocrinology
Adrenal Insufficiency
Cortisol deficiency — Addison's, secondary failure, and the adrenal crisis emergency
Adrenal insufficiency is cortisol deficiency from adrenal destruction (primary Addison's) or pituitary failure (secondary). Primary causes hyperpigmentation from unopposed ACTH. ACTH stim test failed: cortisol <18 µg/dL after Synacthen confirms. Hydrocortisone replacement; adrenal crisis is life-threatening.
- Primary cause (developed world)Autoimmune (anti-21-hydroxylase)
- Secondary cause (most common)Chronic exogenous steroid use
- DiagnosisCortisol <18 µg/dL after 250 µg Synacthen
- HyperpigmentationPrimary only (high ACTH/POMC)
- ReplacementHydrocortisone 15-25 mg/day ± fludrocortisone
- Crisis treatmentIV hydrocortisone 100 mg + 1-2 L saline
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How adrenal insufficiency unfolds
The adrenal cortex makes three classes of steroid hormones from cholesterol: glucocorticoids (cortisol) in the zona fasciculata, mineralocorticoids (aldosterone) in the zona glomerulosa, and adrenal androgens (DHEA) in the zona reticularis. Cortisol production is governed by the HPA axis — hypothalamic CRH drives pituitary ACTH, which stimulates the adrenal cortex; rising cortisol feeds back to suppress both. Aldosterone, by contrast, is driven mainly by the renin-angiotensin system and serum potassium, not by ACTH.
In primary adrenal insufficiency (Addison's disease), the adrenal cortex itself is destroyed — most commonly by autoimmune attack (anti-21-hydroxylase antibodies, T-cell-mediated cortical destruction). Both cortisol AND aldosterone fall, while ACTH rises dramatically because the pituitary still gets the "make more cortisol" signal but the adrenal can't respond. The chronic ACTH surge produces a clinical fingerprint: hyperpigmentation. ACTH derives from pro-opiomelanocortin (POMC), the same precursor that yields melanocyte-stimulating hormone (MSH); when ACTH/POMC is sky-high, melanocyte-1 receptors on skin and mucosa are tonically activated, producing diffuse hyperpigmentation that's most striking in palmar creases, knuckles, buccal mucosa, and recent scars.
In secondary insufficiency, the pituitary or hypothalamus fails. ACTH falls, cortisol falls, but aldosterone is preserved (renin-angiotensin doesn't need ACTH) and hyperpigmentation is absent. The most common cause by far is chronic exogenous steroid therapy that suppressed and atrophied the HPA axis. After abrupt withdrawal or stress, the suppressed axis can't keep up.
Worked clinical example
A 38-year-old woman with type 1 diabetes presents to clinic with 6 months of progressive fatigue, anorexia, 7 kg weight loss, salt craving, lightheadedness when standing, and nausea. She's noticed her palmar creases and knuckles have darkened over the past year, and her gums look bluish. Exam: BP 96/58 supine, 78/52 standing (positive orthostasis), HR 96 supine, 112 standing, hyperpigmented buccal mucosa, dark palmar creases. Labs: Na 128 (low), K 5.7 (high), glucose 72, BUN 24, Cr 1.0, morning cortisol 2.1 µg/dL (low), ACTH 1,840 pg/mL (very high; normal 7-63).
This is primary adrenal insufficiency — the cortisol/ACTH combination is diagnostic without needing an ACTH stim test. Anti-21-hydroxylase antibodies return positive, confirming autoimmune Addison's disease. She's started on hydrocortisone 10 mg on waking, 5 mg at noon, 5 mg at 4 PM, plus fludrocortisone 0.1 mg daily for mineralocorticoid replacement. Counseling: take steroids daily, never miss doses, double or triple dose for fever or moderate illness, IM hydrocortisone 100 mg at home if vomiting or unable to take oral, ED visit for major stress, wear a steroid alert bracelet. At 4-week follow-up: BP 118/72, electrolytes normal, hyperpigmentation slowly fading. Her T1DM was a clue — she's now screened for autoimmune polyglandular syndrome type 2; thyroid and pernicious anemia panels are normal but will be repeated annually.
Primary vs secondary insufficiency — comparison
| Feature | Primary (Addison's) | Secondary (pituitary) |
|---|---|---|
| Site of failure | Adrenal cortex | Pituitary / hypothalamus |
| Most common cause | Autoimmune (~80% developed world) | Chronic exogenous steroid use |
| Cortisol | Low | Low |
| ACTH | High (often >200 pg/mL) | Low or inappropriately normal |
| Aldosterone | Low | Normal (preserved by RAAS) |
| Hyperpigmentation | Yes (POMC/MSH surge) | No |
| Sodium | Low | Low (mild) |
| Potassium | High | Normal |
| Salt craving | Common | Uncommon |
| Treatment | Hydrocortisone + fludrocortisone | Hydrocortisone alone |
Why adrenal insufficiency matters
- Insidious presentation. Vague fatigue and weight loss are dismissed for months — diagnosis often follows crisis.
- Adrenal crisis kills. Untreated crisis has 5-15% mortality; preventable with sick-day rules and patient education.
- Steroid taper failure. The most common cause is iatrogenic — abrupt withdrawal after >2 weeks of supraphysiologic steroids.
- Polyautoimmunity. ~50% of Addison's patients have or develop another autoimmune disease (thyroid, T1DM, vitiligo).
- Surgical stress dosing. Patients on chronic steroids need IV hydrocortisone perioperatively to prevent crisis.
- Pregnancy. Dose increases modestly in third trimester; stress dosing for delivery; close monitoring postpartum.
- Mental health overlap. Fatigue, depression, and weight loss mimic mood disorder — check morning cortisol.
Common misconceptions
- "Hyperpigmentation appears in all adrenal insufficiency." Only primary disease — secondary lacks the ACTH/POMC surge.
- "Wait for stim test before treating crisis." Never delay — give IV hydrocortisone, draw labs simultaneously, ask questions later.
- "Inhaled and topical steroids don't suppress." High-potency or high-dose courses can suppress the HPA axis significantly.
- "Fludrocortisone is always needed." Only in primary disease — aldosterone is preserved in secondary insufficiency.
- "You can stop steroids if you feel better." Replacement is lifelong; abrupt discontinuation precipitates crisis.
- "Addison's is rare and easy to miss." True but check morning cortisol in any patient with vague fatigue, weight loss, hyponatremia, or salt craving.
Frequently asked questions
Primary vs secondary adrenal insufficiency — how are they different?
Primary (Addison's disease) is destruction of the adrenal cortex itself. Cortisol AND aldosterone are deficient. ACTH rises dramatically (no negative feedback). Hyperpigmentation appears because ACTH and MSH share the POMC precursor — high ACTH means high MSH-like signaling. Hyponatremia, hyperkalemia, and orthostatic hypotension reflect aldosterone loss. Causes: autoimmune (~80% in developed world, anti-21-hydroxylase antibodies), TB, fungal, metastases, adrenal hemorrhage (Waterhouse-Friderichsen in meningococcemia), drugs (ketoconazole, etomidate), genetic. Secondary insufficiency is pituitary failure of ACTH production. Cortisol low, aldosterone preserved (RAAS-driven), ACTH low, NO hyperpigmentation, normal potassium, hyponatremia from cortisol deficiency alone. Causes: chronic steroid use (most common), pituitary tumor or surgery, Sheehan, infiltrative disease.
How is adrenal insufficiency diagnosed?
Step 1: morning cortisol (8 AM). Cortisol <3 µg/dL is diagnostic of adrenal insufficiency; >18 µg/dL effectively rules it out; intermediate values need confirmation. Step 2: ACTH stimulation test (cosyntropin/Synacthen) — give 250 µg IV/IM, measure cortisol at 30 and 60 minutes. Peak cortisol <18 µg/dL is diagnostic. Step 3: ACTH level — high (>2× normal) means primary (Addison's); low or normal means secondary. Aldosterone and renin localize further (low aldosterone + high renin = primary). Anti-21-hydroxylase antibodies confirm autoimmune etiology. Adrenal CT for non-autoimmune primary disease. Pituitary MRI for secondary disease.
Why does primary cause hyperpigmentation?
ACTH derives from a precursor protein called pro-opiomelanocortin (POMC), which is cleaved into multiple peptides including ACTH, melanocyte-stimulating hormone (α-MSH and β-MSH), β-endorphin, and lipotropin. ACTH itself also has weak MSH-like activity. In primary adrenal insufficiency, the destroyed cortex can't make cortisol, so negative feedback to the pituitary disappears. ACTH and POMC products surge — chronically high levels stimulate melanocortin-1 receptors on skin melanocytes, increasing melanin synthesis. Hyperpigmentation is generalized but most striking in sun-exposed areas, skin creases (palms, knuckles), buccal mucosa, gums, areolas, recent scars, and pressure points. It's a clinical fingerprint of primary disease that secondary insufficiency does not show.
What is adrenal crisis and how is it treated?
Adrenal crisis is acute, severe cortisol deficiency triggered by stress (infection, surgery, trauma, GI illness, missed steroid doses) in patients with known or unrecognized insufficiency. Features: hypotension (often shock unresponsive to fluids alone), hypoglycemia, hyponatremia, hyperkalemia in primary disease, fever, nausea/vomiting, abdominal pain, altered mental status. Mortality 5-15%. Treatment is immediate and does not wait for confirmation: 100 mg IV hydrocortisone bolus, then 50 mg every 6 hours (or 200 mg/24h continuous infusion). Aggressive IV saline (1-2 L in first hour) — dehydration is profound. Treat hypoglycemia with D50. Identify and treat trigger (often infection). High-dose hydrocortisone has intrinsic mineralocorticoid activity so fludrocortisone isn't needed initially. Taper to maintenance over 2-5 days as illness resolves.
How is chronic adrenal insufficiency treated?
Glucocorticoid replacement: hydrocortisone 15-25 mg/day divided (e.g., 10 mg on waking, 5 mg at noon, 5 mg at 4 PM) to mimic the natural circadian rhythm. Some use prednisone 3-5 mg daily. Avoid bedtime dosing (insomnia). Mineralocorticoid replacement (primary only): fludrocortisone 0.05-0.2 mg daily; monitor BP, electrolytes, renin. DHEA replacement (25-50 mg daily) is optional for women with reduced well-being. Sick-day rules are critical: double or triple the glucocorticoid dose for fever or moderate illness; injectable hydrocortisone (100 mg IM) at home for vomiting or inability to take oral; ED for surgery, trauma, or unresponsive illness. All patients carry steroid alert ID and emergency injection kit.
What causes chronic adrenal suppression from steroids?
Exogenous glucocorticoids (prednisone, dexamethasone, inhaled and topical at high cumulative doses) suppress hypothalamic CRH and pituitary ACTH through negative feedback. The adrenal cortex atrophies from disuse. After 2-3 weeks of supraphysiologic steroid use, abrupt withdrawal can cause symptomatic insufficiency. After months to years of use, recovery of the HPA axis can take 6-12+ months even after careful taper. Steroid taper should be slow (e.g., reduce by 10-20% every 2-4 weeks once below physiologic doses). Patients on long-term steroids need stress dosing for major illness or surgery. ACTH stim test guides return-to-function decisions. This is the most common cause of secondary adrenal insufficiency by far.
What's the prognosis and quality of life on treatment?
With proper replacement, life expectancy approaches normal. Modern lifespan in treated Addison's is 1-2 years below age-matched controls, mostly from adrenal crises (preventable with sick-day rules) and undertreatment. Quality of life is variable — many patients report ongoing fatigue, exercise intolerance, and mood symptoms despite replacement; this likely reflects the rigid dosing of synthetic glucocorticoids vs the body's exquisite minute-to-minute cortisol regulation. Modified-release hydrocortisone (Plenadren) and continuous subcutaneous hydrocortisone pumps are alternatives. Polyautoimmunity is common in Addison's — screen for thyroid disease, T1DM, vitiligo, pernicious anemia, premature ovarian failure (autoimmune polyglandular syndrome type 2). Pregnancy: increase dose modestly in third trimester; stress dosing for delivery.