Endocrine High-Yield Notes for Step 1

Comprehensive vocabulary flashcards covering the high-yield endocrine topics for the USMLE Step 1 based on clinical vignettes, laboratory, and histological features of various endocrine disorders.

Primary adrenal insufficiency (Addison's disease)

Adrenal cortex destruction (often autoimmune or TB) leading to deficiency of cortisol and aldosterone; characterized by hyponatremia, hyperkalemia, hypotension, and hyperpigmentation due to elevated ACTH.

Secondary adrenal insufficiency

Condition caused by low ACTH (e.g., pituitary dysfunction) resulting in low cortisol and androgens, but normal aldosterone levels because aldosterone is regulated by the renin-angiotensin system.

Waterhouse-Friderichsen syndrome

Acute adrenal insufficiency and shock resulting from adrenal hemorrhage associated with Neisseria meningitidis sepsis.

Renal artery stenosis

Decreased kidney perfusion usually caused by atherosclerosis ($>40$ years) or fibromuscular dysplasia ($<40$ years), triggering renin release and secondary hyperaldosteronism; presents with abdominal bruits and increased creatinine after starting lisinopril.

Primary hyperaldosteronism (Conn syndrome)

Adrenal adenoma or bilateral hyperplasia causing excess aldosterone, which leads to sodium retention, potassium loss, hypertension, and suppressed renin levels.

21-hydroxylase deficiency

The most common congenital adrenal hyperplasia; causes shunting to androgens, leading to ambiguous genitalia, hypoglycemia, hyperkalemia, and elevated levels of $17\text{-hydroxyprogesterone}$.

11-beta hydroxylase deficiency

Enzyme deficiency causing excess $11\text{-deoxycorticosterone}$ (which acts like aldosterone) and high androgens, resulting in hypertension, hypokalemia, and virilization.

Ectopic ACTH production

ACTH secretion by non-pituitary tumors (e.g., small cell lung cancer), leading to Cushing syndrome, metabolic alkalosis, and hyperpigmentation; labs show cortisol and ACTH that do not suppress with high-dose dexamethasone.

Exogenous Cushing syndrome

Cushingoid features (e.g., moon facies, abdominal striae) caused by steroid use; characterized by low ACTH and CRH due to negative feedback and a lack of hyperpigmentation.

Pheochromocytoma

Adrenal medulla tumor causing episodic headaches, palpitations, and hypertension; diagnosed by urine or plasma metanephrines and treated with alpha-blockers before beta-blockers.

Neuroblastoma

Adrenal medulla tumor in children originating from neural crest cells; associated with $N\text{-myc}$ amplification, elevated $VMA$ and $HVA$ in urine, and an abdominal mass that crosses the midline.

Primary hyperparathyroidism

Usually caused by a parathyroid adenoma, leading to high calcium, low phosphate, bone cysts, and subperiosteal bone resorption.

Secondary hyperparathyroidism

High PTH triggered by chronic kidney disease (CKD) due to phosphate retention and low calcium; labs show low calcium and high phosphate.

PTHrP (Parathyroid hormone-related peptide)

A peptide secreted by squamous cell carcinoma or renal cell carcinoma that mimics PTH, leading to hypercalcemia and suppressed endogenous PTH.

Sarcoidosis-associated hypercalcemia

A form of hypervitaminosis D where noncaseating granulomas activate vitamin D, leading to high calcium, low PTH, and elevated $1,25(OH)_2$ vitamin D.

Hypomagnesemia

Low magnesium levels that impair the release and action of PTH, causing secondary hypocalcemia and renal potassium wasting.

Rickets

Vitamin D deficiency in children causing defective mineralization of osteoid; presents with bowed legs, craniotabes, rachitic rosary, and widened growth plates.

Sheehan syndrome

Postpartum pituitary infarction following hemorrhage, leading to failure of lactation (low prolactin), amenorrhea, adrenal insufficiency, and hypothyroidism.

Prolactinoma

Most common pituitary adenoma; excess prolactin inhibits GnRH causing low LH/FSH, amenorrhea, galactorrhea, and infertility. Treated with dopamine agonists like cabergoline.

Acromegaly

GH-secreting pituitary adenoma causing coarse facial features and large hands; screened with $IGF\text{-}1$ and confirmed by an oral glucose suppression test where GH fails to suppress.

Carcinoid syndrome

Neuroendocrine tumor (often small intestine) that secretes serotonin after liver metastasis, causing flushing, diarrhea, right-sided heart murmurs, and elevated urine $5\text{-HIAA}$.

Hashimoto thyroiditis

Common autoimmune hypothyroidism associated with anti-TPO antibodies and lymphocytic infiltrate on biopsy; increased risk for thyroid lymphoma.

Subacute thyroiditis (de Quervain)

Granulomatous inflammation of the thyroid following a viral illness; presents with a painful thyroid and elevated ESR.

Graves’ disease

Autoimmune stimulation of TSH receptors by thyroid-stimulating immunoglobulins, leading to hyperthyroidism, exophthalmos, and diffusely increased RAIU scan.

Papillary thyroid carcinoma

Most common thyroid cancer; histological features include Orphan Annie nuclei, psammoma bodies, and nuclear grooves.

Medullary thyroid carcinoma

Tumor of parafollicular C cells producing calcitonin; associated with $RET$ mutations and MEN 2A/2B.

Cretinism

Congenital hypothyroidism due to thyroid dysgenesis; presents with macroglossia, umbilical hernia, hypotonia, and intellectual disability if untreated.

MEN 1

Multiple Endocrine Neoplasia type 1; involves the "3 Ps": Parathyroid adenomas, Pancreatic tumors (like gastrinomas), and Pituitary adenomas.

Central diabetes insipidus

ADH deficiency due to hypothalamic or pituitary injury; presents with polyuria and high serum osmolality ($>285\text{ mOsm/kg}$) that responds to desmopressin.

SIADH

Syndrome of inappropriate ADH secretion causing water retention and euvolemic hyponatremia; labs show low serum osmolality and inappropriately high urine sodium and osmolality.

SGLT2 inhibitor

Diabetes medication (e.g., empagliflozin) that increases renal glucose excretion; side effects include UTIs and vaginal candida infections.

Hyperosmolar hyperglycemic state (HHS)

Severe hyperglycemia in T2DM ($>600\text{ mg/dL}$) causing extreme dehydration and confusion without ketosis.

Diabetic ketoacidosis (DKA)

T1DM complication featuring abdominal pain, Kussmaul breathing, and fruity breath; labs show a high anion gap, low bicarbonate, and hyperkalemia despite low total body potassium.

Glucagonoma

Pancreatic alpha-cell tumor presenting with hyperglycemia, weight loss, and necrolytic migratory erythema.

Ghrelin

Hormone secreted by the stomach that stimulates appetite and gastric motility; levels are abnormally elevated in Prader-Willi syndrome.