Medical terms, defined.

Analgesic nephropathy is a chronic tubulointerstitial nephritis with renal papillary necrosis caused by long-term, high cumulative use of analgesics, classically combination phenacetin/aspirin/caffeine products and now chronic NSAID use....

Primary aldosteronism (Conn syndrome when due to an adenoma) is autonomous aldosterone overproduction by the adrenal zona glomerulosa, independent of the renin-angiotensin system. It causes hypertension, hypokalemia, metabolic alkalosis,...

Renal amyloidosis is extracellular deposition of misfolded, insoluble β-pleated sheet fibrils (Congo red positive, apple-green birefringence under polarized light) in the kidney, most commonly causing nephrotic syndrome. The main types a...

de Quervain (subacute granulomatous) thyroiditis is a self-limited, painful thyroid inflammation, typically following a viral URI, that presents with fever, tender diffusely enlarged thyroid, and elevated ESR. It classically progresses t...

Paraganglioma is a rare neuroendocrine tumor arising from extra-adrenal paraganglia (sympathetic chains or parasympathetic head/neck ganglia). Sympathetic tumors (abdomen/thorax/pelvis, e.g., organ of Zuckerkandl) usually secrete catecho...

Subacute thyroiditis (de Quervain, granulomatous, or subacute granulomatous thyroiditis) is a self-limited, post-viral inflammatory thyroid disease presenting with a painful, tender thyroid, elevated ESR, and transient thyrotoxicosis wit...

Hemophilia B (Christmas disease) is an X-linked recessive bleeding disorder caused by factor IX deficiency or dysfunction. It presents with hemarthroses, deep-tissue/muscle bleeding, and prolonged bleeding after trauma or surgery. Labs s...

Familial hypocalciuric hypercalcemia (FHH) is a benign autosomal dominant disorder caused by inactivating mutations of the calcium-sensing receptor (CaSR; CASR gene). It causes lifelong mild hypercalcemia with low urinary calcium excreti...

11β-hydroxylase deficiency is a form of congenital adrenal hyperplasia (autosomal recessive, CYP11B1 mutation) that blocks conversion of 11-deoxycorticosterone (DOC) to corticosterone and 11-deoxycortisol to cortisol. It causes decreased...

Protein C deficiency is an inherited (autosomal dominant) or acquired thrombophilia caused by reduced protein C, a vitamin K-dependent anticoagulant that inactivates factors Va and VIIIa. It presents with recurrent venous thromboembolism...

Pseudohypoparathyroidism (PHP) is a group of disorders of end-organ resistance to PTH, not deficient PTH. It causes hypocalcemia, hyperphosphatemia, and HIGH PTH. Type 1a is Albright hereditary osteodystrophy (AHO): short stature, round...

17α-hydroxylase deficiency (CYP17A1 mutation) is a rare form of congenital adrenal hyperplasia causing decreased cortisol and sex steroids but increased mineralocorticoids (11-deoxycorticosterone, corticosterone). Presents with hypertens...

Protein S deficiency is an inherited (autosomal dominant) or acquired thrombophilia caused by reduced levels or function of protein S, a vitamin K–dependent cofactor that enhances activated protein C (APC) inactivation of factors Va and...

Antithrombin III (ATIII) deficiency is an inherited (autosomal dominant) or acquired thrombophilia in which reduced ATIII activity causes unchecked thrombin and factor Xa activity, leading to recurrent venous thromboembolism (DVT/PE). It...

Hereditary elliptocytosis (HE) is an autosomal dominant red cell membrane cytoskeleton disorder, usually from defects in spectrin (alpha or beta) or protein 4.1, causing elliptical (oval/cigar-shaped) RBCs on smear. Most patients are asy...

Warm AIHA is the most common type of autoimmune hemolytic anemia, caused by IgG autoantibodies that bind RBCs at body temperature (37°C) and lead to extravascular hemolysis, mainly in the spleen. It is Coombs (direct antiglobulin test) p...

G6PD deficiency is an X-linked recessive enzymatic defect of the HMP (pentose phosphate) shunt that impairs NADPH and reduced glutathione production, making RBCs susceptible to oxidative stress. Triggers (infections, fava beans, sulfa dr...

Alpha thalassemia is an autosomal recessive disorder caused by deletion of one or more of the four α-globin genes (HBA1/HBA2 on chromosome 16), causing reduced α-chain synthesis. It produces a microcytic, hypochromic anemia with severity...

Beta thalassemia is an autosomal recessive disorder caused by reduced (β+) or absent (β0) synthesis of β-globin chains, producing a microcytic, hypochromic anemia. Excess unpaired α-chains precipitate in red cell precursors, causing inef...

Myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem cell disorders causing overproduction of one or more mature myeloid lineages (RBCs, platelets, granulocytes) with preserved maturation. Classic MPNs: CML (BCR-ABL1+), poly...

Marginal zone lymphoma (MZL) is an indolent B-cell non-Hodgkin lymphoma arising from post-germinal center memory B cells of the marginal zone. The classic form is extranodal MZL of mucosa-associated lymphoid tissue (MALT lymphoma), stron...

Arnold-Chiari malformation (Chiari malformation) is a congenital hindbrain anomaly in which the cerebellar tonsils (Type I) or tonsils plus vermis, medulla, and fourth ventricle (Type II) herniate through the foramen magnum. Type I is of...

Dandy-Walker malformation is a congenital posterior fossa anomaly characterized by cerebellar vermis agenesis/hypoplasia, cystic dilation of the fourth ventricle, and an enlarged posterior fossa with upward displacement of the tentorium,...

Neurofibromatosis type 1 (NF1, von Recklinghausen disease) is an autosomal dominant neurocutaneous disorder caused by loss-of-function mutations in the NF1 tumor suppressor gene (chromosome 17q11.2), which encodes neurofibromin, a negati...

Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder caused by loss-of-function mutations in the NF2 tumor suppressor gene (chromosome 22q12) encoding merlin (schwannomin). Hallmark is bilateral vestibular schwannomas (CN VII...

An arteriovenous malformation (AVM) is a congenital tangle of abnormal vessels (the "nidus") in which arteries shunt directly into veins with no intervening capillary bed. This creates a high-flow, low-resistance shunt with thin-walled v...

A lacunar infarct is a small (<15 mm) ischemic stroke caused by occlusion of a deep penetrating end-artery (e.g., lenticulostriate branches of MCA), usually from lipohyalinosis in chronic hypertension (or diabetes). It produces pure moto...

A berry (saccular) aneurysm is a focal outpouching at arterial branch points in the circle of Willis, most commonly the anterior communicating artery. Rupture causes subarachnoid hemorrhage ("worst headache of my life"). Associated with...

A watershed (border-zone) infarct is ischemic tissue injury in the junction zones between two major arterial territories, where perfusion is lowest. It occurs with global hypoperfusion (e.g., hypotension, cardiac arrest, shock) rather th...

A transient ischemic attack (TIA) is a transient episode of focal neurologic dysfunction caused by focal brain, spinal cord, or retinal ischemia WITHOUT acute infarction (tissue-based definition; no DWI lesion). Symptoms typically resolv...

Todd paralysis (postictal paralysis, Todd's palsy) is a transient focal motor weakness following a seizure, typically lasting minutes to hours (usually <48 hours) and resolving completely. It is a diagnosis of exclusion, and stroke must...

A febrile seizure is a seizure occurring in a child aged 6 months to 5 years with fever (≥38°C/100.4°F) without CNS infection, metabolic cause, or prior afebrile seizures. It is the most common childhood seizure type (2-5% of children)....

Lambert-Eaton myasthenic syndrome (LEMS) is a presynaptic neuromuscular junction disorder caused by autoantibodies against presynaptic voltage-gated calcium channels (P/Q-type), reducing acetylcholine release. It presents with proximal m...

Felty syndrome is the triad of rheumatoid arthritis (typically long-standing, seropositive, severe), splenomegaly, and neutropenia. It predisposes to recurrent bacterial infections and is strongly associated with HLA-DR4.

Inclusion body myositis (IBM) is the most common acquired inflammatory myopathy in patients >50 years old, presenting with slowly progressive, often asymmetric weakness of the finger flexors (grip) and quadriceps (falls, knee buckling),...

Pityriasis rosea is a self-limited papulosquamous eruption, typically in young adults, that begins with a single "herald patch" followed 1–2 weeks later by a diffuse rash of oval, salmon-colored scaly plaques in a "Christmas tree" patter...

Acanthosis nigricans is a dermatologic condition of symmetric, hyperpigmented, velvety, thickened plaques in flexural and intertriginous areas (neck, axillae, groin). It is most commonly a cutaneous marker of insulin resistance (obesity,...

Still disease usually means systemic-onset juvenile idiopathic arthritis (sJIA). Its hallmarks are quotidian (daily) spiking fevers, an evanescent salmon-pink rash, and arthritis. Adult-onset Still disease (AOSD) is the adult counterpart...

Melasma is an acquired, symmetric hyperpigmentary disorder of sun-exposed skin, especially the face (cheeks, forehead, upper lip), caused by increased melanin production/deposition. It is classically associated with pregnancy ("mask of p...

Calcium pyrophosphate deposition disease (CPPD, "pseudogout") is a crystal arthropathy caused by deposition of calcium pyrophosphate dihydrate (CPPD) crystals in joints and cartilage. It typically affects older adults, most often the kne...

Keratoacanthoma is a rapidly growing, dome-shaped, well-differentiated squamous cell neoplasm with a central keratin-filled crater, typically on sun-exposed skin of older adults. It grows over weeks to a few months and often regresses sp...

Psoriatic arthritis (PsA) is a seronegative spondyloarthropathy (RF/anti-CCP negative, HLA-B27 associated in axial disease) occurring in ~20-30% of patients with psoriasis. Classic features include asymmetric oligoarthritis, DIP involvem...

Zygomycosis (now mostly called mucormycosis) is an angioinvasive fungal infection caused by Mucorales order molds (Rhizopus, Mucor, Lichtheimia/Absidia), classically in diabetic ketoacidosis or neutropenia/immunocompromise. It presents a...

The fetal period spans week 9 of gestation (embryologic age; ~week 11 gestational age) until birth. It is characterized by growth and maturation of structures formed during the embryonic period (weeks 3–8), rather than by formation of ne...

Epidermolysis bullosa (EB) is a group of inherited blistering disorders caused by mutations in genes encoding structural proteins of the epidermis or dermoepidermal junction, leading to skin/mucosal fragility and blistering after minor t...

The mesonephric (Wolffian) duct is an embryonic paired duct that, under testosterone influence in males, develops into the epididymis, ductus (vas) deferens, seminal vesicles, ejaculatory duct, and appendix epididymis. In females, it reg...

Pierre Robin sequence (PRS) is a triad of micrognathia (small mandible), glossoptosis (posteriorly displaced tongue), and upper airway obstruction, usually with a U-shaped cleft palate. Fetal mandibular hypoplasia causes the tongue to si...

Hardy-Weinberg equilibrium describes a population in which allele and genotype frequencies remain constant from generation to generation. For a two-allele locus, p + q = 1 and p² + 2pq + q² = 1. It is the basis for calculating carrier fr...

The paramesonephric (Müllerian) ducts are paired embryonic structures that, in the absence of SRY/testosterone/AMH, develop into the fallopian tubes, uterus, cervix, and upper one-third of the vagina. In males, Sertoli cell–derived anti-...

DiGeorge sequence (22q11.2 deletion syndrome) results from failure of development of the 3rd and 4th pharyngeal pouches, causing thymic aplasia/hypoplasia (T-cell deficiency), hypoparathyroidism (hypocalcemia), and conotruncal cardiac de...