We're completing our endocrine journey with adrenal disorders - conditions affecting the small but mighty glands that sit atop our kidneys and orchestrate our response to stress. I'll guide you through the complex layers of adrenal physiology, from cortisol excess in Cushing's syndrome to life-threatening cortisol deficiency in Addison's disease. Understanding adrenal function is crucial as these glands produce hormones essential for life, and their dysfunction can present with dramatic, sometimes fatal consequences. Let's explore the intricate world of adrenal regulation!
🩺 Adrenal Physiology and Hormones
The adrenal glands consist of two functionally distinct parts: the cortex producing steroid hormones and the medulla producing catecholamines, each with unique regulatory mechanisms.
Adrenal Cortex Layers
- Zona glomerulosa: Aldosterone (mineralocorticoid)
- Zona fasciculata: Cortisol (glucocorticoid)
- Zona reticularis: Androgens (DHEA, androstenedione)
- Cholesterol-derived steroid hormones
- No storage - synthesis on demand
Adrenal Medulla
- Neural crest origin (modified sympathetic ganglion)
- Produces catecholamines: Epinephrine (80%), norepinephrine (20%)
- Stimulated by sympathetic nervous system
- Fight-or-flight response
- Pheochromocytoma: Catecholamine-secreting tumor
| Hormone | Primary Regulation | Major Functions | Clinical Disorders |
|---|---|---|---|
| Cortisol | HPA axis (CRH → ACTH → cortisol) | Stress response, metabolism, immune modulation, blood pressure | Cushing's syndrome, Addison's disease |
| Aldosterone | RAAS system (angiotensin II, potassium) | Sodium retention, potassium excretion, blood pressure | Hyperaldosteronism, hypoaldosteronism |
| Adrenal Androgens | ACTH (partial regulation) | Weak androgens, precursor for sex steroids | Congenital adrenal hyperplasia, adrenal tumors |
| Catecholamines | Sympathetic nervous system | Fight-or-flight, cardiovascular, metabolic | Pheochromocytoma |
🔄 Cushing's Syndrome: Causes and Pathophysiology
Cushing's syndrome results from chronic glucocorticoid excess, which can be ACTH-dependent or ACTH-independent, with important diagnostic and therapeutic implications.
ACTH-Dependent (80%)
- Cushing's disease: Pituitary adenoma (70%)
- Ectopic ACTH: Small cell lung cancer, carcinoid
- Ectopic CRH: Very rare
- Bilateral adrenal hyperplasia
- High ACTH levels
ACTH-Independent (20%)
- Adrenal adenoma: Cortisol-producing
- Adrenal carcinoma: Often mixed hormone secretion
- Micronodular hyperplasia: Primary pigmented
- Exogenous glucocorticoids: Most common cause overall
- Low ACTH levels
Pseudo-Cushing's
- Alcohol-induced
- Depression/anxiety
- Obesity
- Poorly controlled diabetes
- Physiological stress
Clinical Features of Hypercortisolism
| Feature | Prevalence | Pathophysiology | Clinical Significance |
|---|---|---|---|
| Central obesity | 90% | Increased visceral fat deposition | Moon facies, buffalo hump, truncal obesity |
| Hypertension | 85% | Mineralocorticoid effect, increased vascular sensitivity | Major cardiovascular risk factor |
| Glucose intolerance | 80% | Insulin resistance, increased hepatic gluconeogenesis | Overt diabetes in 20-30% |
| Skin changes | 75% | Protein catabolism, impaired healing | Thin skin, purple striae, easy bruising |
| Muscle weakness | 60% | Protein catabolism, myopathy | Proximal muscle weakness |
| Psychological | 50% | Direct CNS effects | Depression, irritability, cognitive changes |
🔍 Cushing's Syndrome: Diagnosis
Diagnosing Cushing's syndrome requires a stepwise approach: first confirm hypercortisolism, then determine the cause through dynamic testing and imaging.
Diagnostic Algorithm
| Step | Tests | Interpretation | Next Steps |
|---|---|---|---|
| 1. Screen | 24h UFC, late-night salivary cortisol, 1mg DST | 2/3 tests abnormal suggests Cushing's | Proceed to confirmation if screening positive |
| 2. Confirm | 48h 2mg DST, CRH test, midnight serum cortisol | Differentiates true Cushing's from pseudo-Cushing's | Proceed to differential diagnosis if confirmed |
| 3. Differential | Plasma ACTH, high-dose DST, CRH test, IPSS | Distinguishes pituitary, ectopic, adrenal causes | Imaging based on biochemical results |
| 4. Localize | Pituitary MRI, adrenal CT, chest/abdomen CT | Identifies tumor location | Surgical planning |
Key Diagnostic Tests
Screening Tests
- 24h UFC: >3x upper limit of normal
- 1mg DST: Cortisol >1.8 mcg/dL
- Late-night salivary cortisol: Elevated
- High sensitivity but lower specificity
- Perform 2-3 different tests
Differential Tests
- Plasma ACTH: High (ACTH-dependent) vs low (ACTH-independent)
- High-dose DST: Suppression suggests pituitary source
- CRH test: Rise in ACTH suggests pituitary source
- IPSS: Gold standard for pituitary vs ectopic
💊 Cushing's Syndrome Management
Treatment depends on the cause of Cushing's syndrome and aims to normalize cortisol levels while preserving normal pituitary-adrenal function when possible.
Treatment Approaches by Cause
| Cause | First-line Treatment | Alternative Options | Special Considerations |
|---|---|---|---|
| Cushing's Disease (pituitary) | Transsphenoidal surgery | Medication, bilateral adrenalectomy, radiation | Post-op adrenal insufficiency common, requires monitoring |
| Adrenal Adenoma | Unilateral adrenalectomy | Laparoscopic approach preferred | Contralateral adrenal suppression, requires steroid coverage |
| Adrenal Carcinoma | Complete surgical resection | Mitotane, chemotherapy, radiation | Poor prognosis, often metastatic at diagnosis |
| Ectopic ACTH | Resect primary tumor | Medical therapy, bilateral adrenalectomy | Depends on tumor type and resectability |
Medical Therapy Options
Steroidogenesis Inhibitors
- Ketoconazole: Multiple enzyme inhibition
- Metyrapone: 11-beta-hydroxylase inhibitor
- Etomidate: IV for severe Cushing's
- Osilodrostat: New 11-beta-hydroxylase inhibitor
- Monitor LFTs, adrenal function
Other Agents
- Pasireotide: Somatostatin analog
- Mifepristone: Glucocorticoid receptor antagonist
- Cabergoline: Dopamine agonist
- Combination therapy often needed
- Bridge to definitive treatment
🔄 Primary Adrenal Insufficiency (Addison's Disease)
Addison's disease results from adrenal cortex destruction leading to cortisol, aldosterone, and adrenal androgen deficiency, with autoimmune etiology being most common.
Causes
- Autoimmune: 80-90% in developed countries
- Tuberculosis: Leading cause in developing world
- Metastases: Lung, breast, melanoma
- Hemorrhage: Waterhouse-Friderichsen syndrome
- Genetic: Adrenoleukodystrophy, CAH
- Infiltrative: Amyloidosis, sarcoidosis
Autoimmune Features
- Anti-21-hydroxylase antibodies (most specific)
- Associated with other autoimmune diseases
- Autoimmune polyglandular syndrome type 2
- Female predominance (2:1)
- Usually presents age 30-50
Clinical Presentation
- Fatigue, weakness, weight loss
- Hyperpigmentation
- Hypotension, salt craving
- GI symptoms (nausea, vomiting)
- Hypoglycemia
- Often diagnosed during adrenal crisis
Diagnostic Approach
| Test | Finding in Addison's | Interpretation | Clinical Utility |
|---|---|---|---|
| Morning cortisol | Low (<3 mcg/dL diagnostic, <10 suspicious) | Low cortisol suggests adrenal insufficiency | Initial screening test |
| ACTH stimulation test | Low baseline, inadequate response (<18-20 mcg/dL) | Confirms adrenal insufficiency | Gold standard diagnostic test |
| Plasma ACTH | High (>100 pg/mL) | Distinguishes primary from secondary | High ACTH = primary adrenal insufficiency |
| Renin and aldosterone | High renin, low aldosterone | Mineralocorticoid deficiency | Guides fludrocortisone replacement |
| Adrenal antibodies | Positive in autoimmune cases | Identifies autoimmune etiology | Screen for associated autoimmune conditions |
💊 Adrenal Insufficiency Management
Lifelong hormone replacement is required for primary adrenal insufficiency, with glucocorticoid and mineralocorticoid components, plus stress dosing during illness.
Replacement Therapy
| Hormone | Medication | Typical Dose | Monitoring | Special Considerations |
|---|---|---|---|---|
| Glucocorticoid | Hydrocortisone | 15-20 mg/day (2/3 AM, 1/3 PM) or Prednisone 3-5 mg/day |
Clinical symptoms, weight, BP Avoid over-replacement |
Circadian dosing mimics physiology |
| Mineralocorticoid | Fludrocortisone | 0.05-0.2 mg/day | BP, electrolytes, renin level | Only in primary AI, salt craving guide |
| Androgen* | DHEA | 25-50 mg/day | Clinical well-being, libido | Consider in women with low libido, fatigue |
*Androgen replacement is optional and primarily considered for women with persistent fatigue or low libido despite adequate glucocorticoid and mineralocorticoid replacement.
Stress Dosing Guidelines
Minor Stress
- Fever (<38.5°C), minor infection
- Double or triple usual dose
- For 2-3 days until recovery
- Examples: Cold, dental procedure
- No need for parenteral administration
Major Stress
- Fever (>38.5°C), major surgery, trauma
- IV hydrocortisone 50-100 mg q8h
- Continuous infusion may be better
- Taper quickly as stress resolves
- Always have emergency injection available
⚠️ Other Adrenal Disorders
Beyond cortisol disorders, the adrenal glands can produce excess aldosterone or catecholamines, each with distinct clinical presentations and management.
Primary Hyperaldosteronism
- Causes: Aldosterone-producing adenoma (60%), bilateral hyperplasia (40%)
- Presentation: Hypertension, hypokalemia, metabolic alkalosis
- Screening: Aldosterone:renin ratio (>20-30)
- Confirmatory: Salt loading, captopril test
- Treatment: Surgery (adenoma), spironolactone (hyperplasia)
Pheochromocytoma
- Rule of 10s: 10% bilateral, 10% extra-adrenal, 10% malignant, 10% familial
- Presentation: Episodic hypertension, headache, sweating, palpitations
- Diagnosis: Plasma or urine metanephrines
- Localization: CT/MRI, MIBG scan
- Treatment: Alpha-blockade pre-op, then surgical resection
Congenital Adrenal Hyperplasia (CAH)
| Enzyme Deficiency | Hormone Pattern | Clinical Features | Treatment |
|---|---|---|---|
| 21-hydroxylase (90-95%) | Low cortisol, aldosterone High androgens, 17-OHP |
Salt-wasting or simple virilizing Ambiguous genitalia (females) |
Glucocorticoids, mineralocorticoids |
| 11-beta-hydroxylase (5-8%) | Low cortisol, high androgens High 11-deoxycortisol, DOC |
Hypertension, hypokalemia Virilization |
Glucocorticoids |
| 17-alpha-hydroxylase (rare) | Low cortisol, androgens High DOC, corticosterone |
Hypertension, hypokalemia Sexual infantilism |
Glucocorticoids, sex hormones |
🧠 Key Takeaways
- Adrenal cortex produces cortisol, aldosterone, and androgens
- Cushing's syndrome results from chronic glucocorticoid excess
- Addison's disease is primary adrenal insufficiency, most often autoimmune
- Diagnosis requires stepwise testing: screen → confirm → differentiate → localize
- Adrenal crisis is life-threatening and requires immediate IV hydrocortisone
- Lifelong replacement therapy needed for adrenal insufficiency
- Stress dosing is crucial during illness or procedures
- Other important disorders: hyperaldosteronism, pheochromocytoma, CAH
🧭 Conclusion
We've completed our comprehensive exploration of adrenal disorders, student—from the dramatic presentations of Cushing's syndrome to the insidious onset of Addison's disease and the explosive nature of pheochromocytoma. Remember that adrenal disorders span the spectrum from subtle chronic illness to life-threatening emergencies, requiring both diagnostic precision and therapeutic vigilance. I encourage you to master the art of adrenal testing interpretation and the crucial principles of glucocorticoid replacement and stress dosing. Excellent work completing the endocrine and metabolic disorders section! Next, we'll move to hematology, starting with anemias and their diverse causes.
In adrenal disorders, the margin between adequate replacement and over-treatment is narrow, and the consequences of under-treatment during stress can be fatal - careful monitoring and patient education are paramount.