USMLE Step 1 & 2 Adrenal Disorders (Addison's, Cushing's)
Last updated: May 2, 2026
Adrenal Disorders (Addison's, Cushing's) questions are one of the highest-leverage areas to study for the USMLE Step 1 & 2. This guide breaks down the rule, the elements you need to recognize, the named traps that catch most students, and a memory aid that scales to test day. Read it once, then practice the same sub-topic adaptively in the app.
The rule
Adrenal disorders are localized by pairing the cortisol level with the ACTH level. Low cortisol with high ACTH means primary adrenal failure (Addison's); low cortisol with low/normal ACTH means secondary (pituitary) or tertiary (hypothalamic/exogenous-steroid) insufficiency. High cortisol with high ACTH means ACTH-dependent Cushing's (pituitary adenoma = Cushing disease, or ectopic ACTH from small-cell lung cancer or carcinoid); high cortisol with suppressed ACTH means ACTH-independent disease (adrenal adenoma, carcinoma, or exogenous glucocorticoid). Once you have the ACTH bucket, the next test (high-dose dexamethasone, CRH, imaging) follows automatically.
Elements breakdown
Primary adrenal insufficiency (Addison's)
Destruction of the adrenal cortex; loss of cortisol AND aldosterone.
- Low cortisol, high ACTH, low aldosterone
- Hyponatremia, hyperkalemia, mild non-anion-gap acidosis
- Hyperpigmentation of skin/buccal mucosa
- Autoimmune adrenalitis is the #1 cause in developed world
- Cosyntropin (ACTH-stim) test: cortisol fails to rise
Common examples:
- Autoimmune adrenalitis
- Tuberculous adrenalitis
- Waterhouse-Friderichsen (meningococcemia)
- Metastatic disease to adrenals
Secondary/tertiary adrenal insufficiency
Pituitary or hypothalamic failure, or chronic exogenous steroids suppressing the HPA axis.
- Low cortisol, low/normal ACTH
- Aldosterone preserved (RAAS still drives it)
- No hyperkalemia, no hyperpigmentation
- Hyponatremia possible from cortisol-mediated free-water retention
- Most common cause: abrupt steroid taper
Cushing disease (ACTH-dependent, pituitary)
ACTH-secreting pituitary adenoma, usually a microadenoma.
- High cortisol, high ACTH
- Suppresses with HIGH-dose dexamethasone
- Positive response to CRH stimulation
- MRI pituitary for the lesion
- Most common endogenous cause of Cushing's
Ectopic ACTH syndrome
Non-pituitary tumor secretes ACTH, classically small-cell lung carcinoma.
- High cortisol, very high ACTH
- Does NOT suppress with high-dose dexamethasone
- Blunted/absent response to CRH
- Rapid onset, profound hypokalemia, weight loss > weight gain
- CT chest/abdomen for source
ACTH-independent (adrenal) Cushing's
Adrenal adenoma, carcinoma, or bilateral hyperplasia autonomously producing cortisol.
- High cortisol, suppressed ACTH
- No suppression with any dose of dexamethasone
- Adrenal CT/MRI to localize
- Carcinoma: large (>4 cm), heterogeneous, may co-secrete androgens
Exogenous glucocorticoid (iatrogenic)
Most common cause of Cushingoid features overall.
- High clinical cortisol effect, but LOW measured cortisol
- Low ACTH (suppressed axis)
- Bilateral adrenal atrophy on imaging
- History of prednisone, inhaled/topical/intra-articular steroids
Common patterns and traps
The ACTH-First Localization Algorithm
Once cortisol abnormality is confirmed, ACTH is the single most useful next test. It splits the differential into ACTH-dependent versus ACTH-independent halves and dictates whether the next imaging study is pituitary MRI, chest/abdomen CT, or adrenal CT. Skipping ACTH and jumping to imaging is the single most common workup error tested.
A correct answer choice will say 'measure plasma ACTH' or 'serum ACTH level' as the next step after confirmed hypercortisolism or hypocortisolism, before any imaging.
The Hyperpigmentation Tell
In primary adrenal insufficiency, pituitary corticotrophs cleave POMC into ACTH and MSH-like fragments. Elevated ACTH/POMC products stimulate melanocytes, producing characteristic darkening of palmar creases, buccal mucosa, scars, and sun-exposed areas. Secondary insufficiency (low ACTH) does NOT cause hyperpigmentation — this is one of the cleanest exam discriminators.
A vignette mentioning 'darkening of the gums' or 'hyperpigmented palmar creases' alongside fatigue and hyponatremia is signaling primary Addison's, not pituitary disease.
The Steroid-Withdrawal Mimic
Patients on chronic glucocorticoids who taper too quickly, miss doses during illness, or have steroids stopped abruptly can present with adrenal crisis indistinguishable from Addison's clinically — except aldosterone is preserved (no hyperkalemia) and ACTH is low. The history of inhaled, topical, intra-articular, or oral steroids is the giveaway, and the test wants you to recognize this without ordering more labs.
A vignette with months of prednisone for autoimmune disease, recent rapid taper, now hypotensive and weak — the answer is stress-dose hydrocortisone, not 'check 21-hydroxylase antibodies.'
The Ectopic ACTH Pattern
A smoker with weight LOSS (not gain), profound hypokalemia, metabolic alkalosis, hyperglycemia, and hyperpigmentation, evolving over weeks rather than years, is classic ectopic ACTH from small-cell lung cancer. The cortisol levels are so high that mineralocorticoid receptor crossover causes the hypokalemic alkalosis. Failure to suppress with high-dose dexamethasone seals it.
A choice naming 'small cell carcinoma of the lung' or 'CT of the chest' will be correct when the picture is rapid-onset Cushingoid features with hypokalemia in a smoker.
The Adrenal Crisis Trigger
Known or suspected adrenal insufficiency plus a physiologic stressor (infection, surgery, trauma) precipitates crisis: hypotension refractory to fluids, hyponatremia, hyperkalemia, hypoglycemia. The exam wants immediate IV hydrocortisone and IV fluids BEFORE confirmatory testing — diagnosis can wait, treatment cannot.
A choice that says 'administer IV hydrocortisone and normal saline' will beat 'order cosyntropin stimulation test' when the patient is acutely hypotensive.
How it works
Picture Ms. Alvarez, a 38-year-old with central obesity, purple striae, proximal weakness, and new diabetes. Step one is to confirm hypercortisolism: 24-hour urinary free cortisol, late-night salivary cortisol, or low-dose dexamethasone suppression. Once confirmed, you measure ACTH. If ACTH is suppressed, the adrenal is autonomous — get an adrenal CT. If ACTH is high or inappropriately normal, you are ACTH-dependent, and the question becomes pituitary versus ectopic. High-dose dexamethasone suppresses pituitary adenomas (they retain some feedback) but not ectopic tumors; CRH stimulates pituitary ACTH but not ectopic. Inferior petrosal sinus sampling is the gold standard when biochemistry and MRI disagree. The exact same logic in reverse handles insufficiency: confirm low cortisol, then let ACTH localize the lesion above or at the adrenal.
Worked examples
Which of the following is the most likely underlying cause of this patient's presentation?
- A Autoimmune destruction of the adrenal cortex ✓ Correct
- B ACTH-secreting pituitary microadenoma
- C Chronic exogenous glucocorticoid use with abrupt cessation
- D Cortisol-secreting adrenal adenoma
Why A is correct: The triad of hyponatremia, hyperkalemia, and hypotension with hyperpigmentation of palmar creases, buccal mucosa, and an old scar is pathognomonic for primary adrenal insufficiency. Hyperpigmentation reflects elevated POMC-derived ACTH/MSH activity on melanocytes, which only occurs when ACTH is high — i.e., primary disease. In a developed-country setting without a TB or HIV history, autoimmune adrenalitis is the most common etiology and would be confirmed with 21-hydroxylase antibodies and a failed cosyntropin stimulation test.
Why each wrong choice fails:
- B: A pituitary ACTH-secreting adenoma causes Cushing disease (cortisol EXCESS), not deficiency, and would present with central obesity and striae rather than weight loss and hypotension. The cortisol of 3 µg/dL rules out hypercortisolism entirely. (The ACTH-First Localization Algorithm)
- C: Steroid-withdrawal insufficiency would suppress ACTH, so there would be NO hyperpigmentation, and aldosterone would be preserved — meaning no hyperkalemia. The hyperkalemia and pigmentation here mandate primary disease. (The Steroid-Withdrawal Mimic)
- D: A cortisol-secreting adenoma produces ACTH-independent Cushing's with hypertension, hyperglycemia, and weight gain — the opposite of this patient's hypotension, hypoglycemia, and weight loss. (The ACTH-First Localization Algorithm)
Which of the following is the most likely diagnosis?
- A Adrenal cortical carcinoma
- B Cushing disease (pituitary corticotroph adenoma) ✓ Correct
- C Ectopic ACTH syndrome from small-cell lung carcinoma
- D Exogenous glucocorticoid administration
Why B is correct: Confirmed hypercortisolism with elevated ACTH places this in the ACTH-dependent category. Suppression of cortisol by more than 50% with high-dose dexamethasone indicates retained negative feedback typical of a pituitary corticotroph adenoma, which still expresses glucocorticoid receptors. Combined with a 5-mm sellar lesion on MRI, this is textbook Cushing disease.
Why each wrong choice fails:
- A: Adrenal cortical carcinoma is ACTH-INDEPENDENT, so plasma ACTH would be suppressed (<5 pg/mL), not elevated to 92. It also typically presents with rapid virilization or feminization from co-secreted sex steroids and a large adrenal mass on imaging. (The ACTH-First Localization Algorithm)
- C: Ectopic ACTH classically does NOT suppress with high-dose dexamethasone and presents with rapid onset, profound hypokalemia, and weight loss in a smoker. The 75% suppression and the indolent course over six months argue against this. (The Ectopic ACTH Pattern)
- D: Exogenous glucocorticoid use suppresses both ACTH and endogenous cortisol — measured serum/urinary cortisol would be LOW, not markedly elevated. The lab pattern here rules out an iatrogenic cause. (The Steroid-Withdrawal Mimic)
Which of the following is the most appropriate next step?
- A Pituitary MRI with gadolinium
- B Bilateral adrenalectomy
- C CT of the chest, abdomen, and pelvis ✓ Correct
- D Begin hydrocortisone replacement therapy
Why C is correct: Hypercortisolism with markedly elevated ACTH that fails to suppress with high-dose dexamethasone, combined with rapid onset, severe hypokalemic metabolic alkalosis, hyperglycemia, weight loss, and a heavy smoking history, points to ectopic ACTH syndrome — most commonly from small-cell lung carcinoma. The next step is to localize the source with CT imaging of the chest, abdomen, and pelvis. Pituitary MRI is unhelpful because the disease is extracranial.
Why each wrong choice fails:
- A: Pituitary MRI is the right move when high-dose dexamethasone SUPPRESSES cortisol (suggesting Cushing disease). Here, only 12% suppression argues strongly against a pituitary source, so imaging the pituitary first wastes time and can mislead with incidental microadenomas. (The ACTH-First Localization Algorithm)
- B: Bilateral adrenalectomy is a salvage therapy for refractory hypercortisolism, not a diagnostic step, and it would miss the underlying lung malignancy that is the actual life-limiting disease.
- D: This patient has cortisol EXCESS, not deficiency — giving hydrocortisone would worsen the hypercortisolism. Hydrocortisone replacement is the answer for adrenal crisis, which presents with hypotension, hyperkalemia, and hypoglycemia. (The Adrenal Crisis Trigger)
Memory aid
"High ACTH points UP, low ACTH points DOWN." High ACTH = problem above the adrenal (pituitary tumor in Cushing's, adrenal destruction in Addison's making the pituitary scream). Low ACTH = problem at or below the pituitary level (autonomous adrenal in Cushing's, pituitary failure in Addison-like picture). For Addison vs. secondary: "Pigment & Potassium = Primary." Hyperpigmentation and hyperkalemia together nail the adrenal as the failing organ.
Key distinction
Cushing disease (pituitary adenoma) vs. ectopic ACTH (small-cell lung cancer): both have high cortisol and high ACTH. High-dose dexamethasone SUPPRESSES Cushing disease but NOT ectopic ACTH; CRH STIMULATES Cushing disease but NOT ectopic. Ectopic also tends to present with rapid onset, profound hypokalemic alkalosis, hyperpigmentation, and weight loss rather than the classic central obesity.
Summary
Pair cortisol with ACTH first — the ACTH bucket tells you whether the lesion is in the adrenal, pituitary, or somewhere ectopic, and dictates the next test.
Practice adrenal disorders (addison's, cushing's) adaptively
Reading the rule is the start. Working USMLE Step 1 & 2-format questions on this sub-topic with adaptive selection, watching your mastery score climb in real time, and seeing the items you missed return on a spaced-repetition schedule — that's where score lift actually happens. Free for seven days. No credit card required.
Start your free 7-day trialFrequently asked questions
What is adrenal disorders (addison's, cushing's) on the USMLE Step 1 & 2?
Adrenal disorders are localized by pairing the cortisol level with the ACTH level. Low cortisol with high ACTH means primary adrenal failure (Addison's); low cortisol with low/normal ACTH means secondary (pituitary) or tertiary (hypothalamic/exogenous-steroid) insufficiency. High cortisol with high ACTH means ACTH-dependent Cushing's (pituitary adenoma = Cushing disease, or ectopic ACTH from small-cell lung cancer or carcinoid); high cortisol with suppressed ACTH means ACTH-independent disease (adrenal adenoma, carcinoma, or exogenous glucocorticoid). Once you have the ACTH bucket, the next test (high-dose dexamethasone, CRH, imaging) follows automatically.
How do I practice adrenal disorders (addison's, cushing's) questions?
The fastest way to improve on adrenal disorders (addison's, cushing's) is targeted, adaptive practice — working questions that focus on your specific weak spots within this sub-topic, getting immediate feedback, and revisiting items you missed on a spaced-repetition schedule. Neureto's adaptive engine does this automatically across the USMLE Step 1 & 2; start a free 7-day trial to see your sub-topic mastery climb in real time.
What's the most important distinction to remember for adrenal disorders (addison's, cushing's)?
Cushing disease (pituitary adenoma) vs. ectopic ACTH (small-cell lung cancer): both have high cortisol and high ACTH. High-dose dexamethasone SUPPRESSES Cushing disease but NOT ectopic ACTH; CRH STIMULATES Cushing disease but NOT ectopic. Ectopic also tends to present with rapid onset, profound hypokalemic alkalosis, hyperpigmentation, and weight loss rather than the classic central obesity.
Is there a memory aid for adrenal disorders (addison's, cushing's) questions?
"High ACTH points UP, low ACTH points DOWN." High ACTH = problem above the adrenal (pituitary tumor in Cushing's, adrenal destruction in Addison's making the pituitary scream). Low ACTH = problem at or below the pituitary level (autonomous adrenal in Cushing's, pituitary failure in Addison-like picture). For Addison vs. secondary: "Pigment & Potassium = Primary." Hyperpigmentation and hyperkalemia together nail the adrenal as the failing organ.
What's a common trap on adrenal disorders (addison's, cushing's) questions?
Forgetting that exogenous steroids are the #1 cause of Cushingoid features
What's a common trap on adrenal disorders (addison's, cushing's) questions?
Calling hyperkalemia in secondary insufficiency (aldosterone is preserved — there shouldn't be any)
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