The Endocrine confusions that cost the most Step 1 points

Endocrine look-alikes cost points because the same symptoms can fit more than one disorder. For each pair, focus on the single clue that separates the two.

Hyperthyroidism vs Pheochromocytoma

Both can cause sweating, tachycardia, anxiety, and weight loss. Hyperthyroidism causes sustained metabolic overdrive with heat intolerance, tremor, goiter, hyperdefecation, low TSH, and high thyroid hormone. Pheochromocytoma causes episodic catecholamine surges with headache, sweating, palpitations, and severe paroxysmal hypertension. Do not choose based on adrenergic symptoms alone because the deciding clue is whether the pattern is continuous or episodic.

Hyperthyroidism vs Pheochromocytoma Thyroid excess is sustained metabolic overdrive; pheochromocytoma is episodic catecholamine storm. Open the comparison and video →

DKA vs HHS

Both cause dehydration and can present with marked hyperglycemia. DKA is separated by ketones, anion-gap metabolic acidosis, abdominal pain, and Kussmaul respirations. HHS is separated by hyperosmolality, altered mental status, absent or mild ketones, and little acidosis. Do not let the glucose level decide when the ketone and acid-base profile gives you the answer.

DKA vs HHS DKA is ketotic anion-gap acidosis; HHS is hyperosmolar dehydration with absent or mild ketones and little acidosis. Open the comparison and video →

Primary adrenal insufficiency vs Secondary adrenal insufficiency

Both can cause hypotension, fatigue, hyponatremia, and hypoglycemia. Primary adrenal insufficiency has high ACTH, hyperpigmentation, hyperkalemia, and loss of both cortisol and aldosterone. Secondary adrenal insufficiency has low ACTH, preserved aldosterone, normal potassium, and no ACTH-driven hyperpigmentation. Use ACTH, potassium, and skin pigmentation instead of relying on the shared sodium and energy symptoms.

Primary adrenal insufficiency vs Secondary adrenal insufficiency Primary has high ACTH and mineralocorticoid loss; secondary has low ACTH and preserved aldosterone. Open the comparison and video →

Central diabetes insipidus vs Nephrogenic diabetes insipidus

Both can cause polyuria, dilute urine, and hypernatremia when water access is limited. In central diabetes insipidus, low ADH production is the problem, so desmopressin causes the urine to concentrate. In nephrogenic diabetes insipidus, the kidney cannot respond to ADH, so the urine stays dilute after desmopressin. Use that response to decide whether the problem is hormone supply or kidney response.

Central diabetes insipidus vs Nephrogenic diabetes insipidus Central DI responds to desmopressin with urine concentration; nephrogenic DI stays dilute because the kidney cannot respond. Open the comparison and video →

Septic shock vs Adrenal crisis

Both can involve severe hypotension, and infection can trigger adrenal crisis. Septic shock is led by infection, with fever, high lactate, vasodilation, and poor perfusion. Adrenal crisis is separated by refractory hypotension plus cortisol-failure clues such as hyponatremia, hypoglycemia, sometimes hyperkalemia, and a history of steroid exposure. Do not exclude adrenal crisis just because you identify an infection.

Septic shock vs Adrenal crisis Sepsis is infection-led shock; adrenal crisis is refractory shock plus cortisol-failure clues and steroid history. Open the comparison and video →

Endogenous Cushing syndrome vs Exogenous glucocorticoid effect

Both can produce Cushingoid features. Endogenous Cushing syndrome comes from cortisol produced by pituitary, ectopic, or adrenal disease and has abnormal cortisol screening. Exogenous glucocorticoid effect comes from outside glucocorticoid exposure, which suppresses CRH, ACTH, and endogenous cortisol production. Check the medication history and ACTH-cortisol pattern before trying to localize a source.

Endogenous Cushing syndrome vs Exogenous glucocorticoid effect Endogenous Cushing makes cortisol internally; exogenous steroid use suppresses the axis from outside. Open the comparison and video →

Primary hyperparathyroidism vs Malignancy hypercalcemia

Both can cause the same hypercalcemia symptoms, including stones, bone pain, abdominal symptoms, psychiatric symptoms, polyuria, and constipation. Primary hyperparathyroidism has high or inappropriately normal PTH with elevated calcium. Malignancy hypercalcemia has suppressed PTH and may be associated with weight loss, a cancer history, PTHrP, or lytic bone lesions. Measure PTH with calcium because symptoms alone cannot separate them.

Primary hyperparathyroidism vs Malignancy hypercalcemia High PTH means parathyroid source; low PTH means look for malignancy or another non-PTH cause. Open the comparison and video →

Graves disease vs Subacute thyroiditis

Both can cause low TSH, elevated free T4 and T3, palpitations, weight loss, and heat intolerance. Graves disease actively makes new hormone, with a diffuse nontender goiter, eye findings, thyroid-stimulating antibodies, and high diffuse uptake. Subacute thyroiditis leaks stored hormone, with a painful tender thyroid after a viral illness and near-zero uptake. Do not rely on thyroid labs alone when the thyroid exam and radioactive iodine uptake reveal the cause.

Graves disease vs Subacute thyroiditis Graves actively makes new hormone with high uptake; thyroiditis leaks stored hormone with low uptake. Open the comparison and video →

Quick self-test

Name the diagnosis from the clue, then tap to check.

1. Weight loss, heat intolerance, tremor, goiter, hyperdefecation, low TSH, and high thyroid hormone.

   Hyperthyroidism · Hyperthyroidism vs Pheochromocytoma

2. Low ADH production from hypothalamic or posterior pituitary dysfunction with intact renal responsiveness.

   Central diabetes insipidus · Central diabetes insipidus vs Nephrogenic diabetes insipidus

3. Hypercalcemia with inappropriately high PTH, kidney stones, bone pain, or psychiatric/GI symptoms.

   Primary hyperparathyroidism · Primary hyperparathyroidism vs Malignancy hypercalcemia

4. Episodic headache, sweating, palpitations, and severe paroxysmal hypertension.

   Pheochromocytoma · Hyperthyroidism vs Pheochromocytoma

5. Pituitary or steroid-withdrawal cortisol deficiency with low ACTH, preserved aldosterone, and no ACTH-driven hyperpigmentation.

   Secondary adrenal insufficiency · Primary adrenal insufficiency vs Secondary adrenal insufficiency

6. Refractory hypotension despite fluids or pressors with steroid history, hyponatremia, hypoglycemia, and sometimes hyperkalemia.

   Adrenal crisis · Septic shock vs Adrenal crisis

7. Hyperthyroidism with diffuse goiter, eye findings, thyroid-stimulating antibodies, and high uptake.

   Graves disease · Graves disease vs Subacute thyroiditis

8. Ketones, anion gap metabolic acidosis, abdominal pain, Kussmaul respirations, and dehydration.

   DKA · DKA vs HHS

9. Renal resistance to ADH, classically from lithium, hypercalcemia, hypokalemia, or inherited collecting-duct defects.

   Nephrogenic diabetes insipidus · Central diabetes insipidus vs Nephrogenic diabetes insipidus

10. Infection-driven hypotension with fever, high lactate, vasodilation, and poor perfusion.

    Septic shock · Septic shock vs Adrenal crisis

11. Painful tender thyroid after viral illness with transient thyrotoxicosis and low uptake.

    Subacute thyroiditis · Graves disease vs Subacute thyroiditis

12. Extreme hyperglycemia, hyperosmolality, altered mental status, and absent or mild ketones.

    HHS · DKA vs HHS

How to make these stick

Practice each pair with fresh questions until you recognize the separating clue without hesitation. Keep going until the distinction feels automatic.