Medical terms, defined.

Bence Jones proteins are free monoclonal immunoglobulin light chains (kappa or lambda) found in the urine, classically associated with multiple myeloma and other plasma cell dyscrasias. They are not detected by standard urine dipstick (w...

1,3-β-glucan synthase is a fungal cell wall enzyme that synthesizes β-(1,3)-D-glucan, an essential structural polysaccharide. It is the molecular target of the echinocandin class of antifungal drugs (caspofungin, micafungin, anidulafungin).

CYP51 (lanosterol 14α-demethylase) is a fungal cytochrome P450 enzyme essential for converting lanosterol to ergosterol, a critical component of the fungal cell membrane. It is the molecular target of azole antifungal drugs. Inhibition o...

14α-demethylase (lanosterol 14α-demethylase, CYP51) is a fungal cytochrome P450 enzyme that converts lanosterol to ergosterol, an essential component of the fungal cell membrane. It is the molecular target of azole antifungal drugs. Inhi...

Nystatin is a polyene antifungal used primarily for Candida infections, particularly oral thrush, esophageal candidiasis, and cutaneous/vaginal candidiasis. It is not absorbed systemically when given orally, so it is used topically or as...

Lanosterol is a tetracyclic triterpenoid that serves as the first sterol intermediate in cholesterol biosynthesis, formed from squalene via squalene epoxide cyclization. It is a key precursor from which cholesterol is synthesized through...

Ergosterol is the principal sterol in fungal cell membranes, analogous to cholesterol in human cell membranes. It maintains membrane fluidity and integrity in fungi and is the key target of several major classes of antifungal drugs.

Flucytosine (5-FC) is an antifungal pyrimidine analog used primarily in combination with amphotericin B for severe systemic fungal infections, especially cryptococcal meningitis. It works by being converted intracellularly into fluoroura...

Polyenes are antifungal agents (e.g., amphotericin B, nystatin) that bind ergosterol in fungal cell membranes, creating pores that cause leakage of cellular contents and fungal death. Amphotericin B is used for severe systemic fungal inf...

Zileuton is a 5-lipoxygenase (5-LOX) inhibitor used in the treatment of chronic asthma. By blocking 5-LOX, it prevents the conversion of arachidonic acid to leukotrienes, reducing bronchoconstriction and inflammation. It is less commonly...

Selective estrogen receptor modulators (SERMs) are drugs that act as estrogen receptor agonists in some tissues and antagonists in others, allowing tissue-specific modulation of estrogenic effects. Key examples include tamoxifen, raloxif...

Serum sickness-like reaction (SSLR) is a type III hypersensitivity-like reaction occurring days after exposure to certain drugs (classically cefaclor, amoxicillin, or other antibiotics), presenting with fever, urticarial/serpiginous rash...

Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disease characterized by production of autoantibodies (notably ANA and anti-dsDNA) that cause multisystem inflammation and tissue damage. It predominantly affects women of childb...

Subacute combined degeneration (SCD) is a neurological disorder caused by vitamin B12 (cobalamin) deficiency, resulting in demyelination of the dorsal columns and lateral corticospinal tracts of the spinal cord. It presents with a combin...

Loratadine is a second-generation H1 antihistamine used to treat allergic rhinitis, conjunctivitis, and urticaria. Unlike first-generation antihistamines (e.g., diphenhydramine), it has minimal CNS penetration, resulting in significantly...

Second-generation H1 antihistamines (e.g., loratadine, cetirizine, fexofenadine, desloratadine) selectively block peripheral H1 receptors with minimal CNS penetration, making them less sedating than first-generation agents. They are firs...

Chikungunya is a mosquito-borne viral illness caused by an alphavirus (Togaviridae family), transmitted by Aedes aegypti and Aedes albopictus mosquitoes. It presents with abrupt high fever and severe, often debilitating polyarthralgia, d...

Hutchinson teeth are peg-shaped, widely spaced upper central incisors with a notched biting edge, caused by congenital syphilis. They are one component of Hutchinson's triad, which also includes interstitial keratitis and sensorineural d...

Asplenia is the absence of splenic function, either anatomic (surgical splenectomy, congenital absence) or functional (sickle cell disease autosplenectomy). It causes impaired clearance of encapsulated organisms (S. pneumoniae, H. influe...

HbC disease is a hemoglobinopathy caused by a point mutation in the β-globin gene (codon 6, glutamic acid → lysine; GAG→AAG), producing hemoglobin C. Homozygotes (HbCC) have a mild chronic hemolytic anemia with splenomegaly and numerous...

The Tzanck smear is a rapid cytologic test used to diagnose vesiculobullous skin disorders, most notably herpes simplex virus (HSV) and varicella-zoster virus (VZV) infections. It involves scraping the base of a fresh vesicle and stainin...

T-cell Acute Lymphoblastic Leukemia/Lymphoma (T-ALL) is an aggressive malignancy of immature T-cell precursors, commonly presenting in adolescent males as a mediastinal (thymic) mass causing superior vena cava syndrome. It is classified...

Terminal deoxynucleotidyl transferase (TdT) is a DNA polymerase expressed in immature pre-B and pre-T lymphocytes (lymphoblasts). It is a key immunohistochemical marker used to distinguish acute lymphoblastic leukemia/lymphoma (ALL/LBL)...

Argyll Robertson pupils are small, irregular pupils that constrict with accommodation (near vision) but fail to constrict in response to light—classically described as 'accommodates but does not react.' This finding is a classic sign of...

Allylamines are antifungal drugs (e.g., terbinafine, naftifine) that inhibit fungal squalene epoxidase, blocking ergosterol synthesis and causing toxic accumulation of squalene within the fungal cell. They are primarily used for dermatop...

Keratoconjunctivitis sicca (dry eye syndrome) results from decreased tear production or increased tear evaporation, leading to dryness and irritation of the cornea and conjunctiva. It is a hallmark feature of Sjögren syndrome but can als...

Rifamycins (rifampin, rifabutin, rifapentine) are antibiotics that inhibit bacterial DNA-dependent RNA polymerase, blocking transcription. They are first-line agents for tuberculosis and are also used for prophylaxis against Neisseria me...

AL (primary) amyloidosis results from clonal plasma cell dyscrasias that produce misfolded immunoglobulin light chains (lambda > kappa), which deposit as amyloid fibrils in tissues. It commonly affects the heart, kidneys, liver, peripher...

Adult T-cell leukemia/lymphoma (ATLL) is a peripheral T-cell neoplasm caused by HTLV-1 (Human T-lymphotropic virus 1) infection, endemic to Japan, the Caribbean, and parts of Africa. It classically presents with the tetrad of hypercalcem...

Adult T-cell Leukemia/Lymphoma (ATLL) is an aggressive malignancy of mature CD4+ T-cells caused by infection with Human T-lymphotropic virus type 1 (HTLV-1). It is endemic in regions like Japan, the Caribbean, and parts of Africa, and tr...

MALToma (mucosa-associated lymphoid tissue lymphoma) is a type of extranodal marginal zone B-cell lymphoma that arises in mucosal tissues, most commonly the stomach. It is strongly associated with chronic inflammatory conditions, particu...

Sulfadiazine is a sulfonamide antibiotic that inhibits dihydropteroate synthase, blocking folate synthesis in bacteria and parasites. It is classically combined with pyrimethamine for treating toxoplasmosis, especially in immunocompromis...

IL-8 (CXCL8) is a chemokine primarily responsible for neutrophil chemotaxis and activation at sites of acute inflammation. It is released by macrophages, endothelial cells, and epithelial cells in response to infection or tissue injury,...

IκB kinase (IKK) is an enzyme complex that phosphorylates IκB, the inhibitory protein bound to NF-κB. Phosphorylation marks IκB for ubiquitination and proteasomal degradation, releasing NF-κB to translocate to the nucleus and activate tr...

PAX8 is a transcription factor critical for the development of the thyroid, kidney, and Müllerian (female reproductive) tract. It serves as an important immunohistochemical marker in surgical pathology for identifying tumors of thyroid,...

Pope's blessing (also called 'hand of benediction') describes the characteristic hand posture seen with certain median nerve lesions, particularly proximal lesions at the wrist/elbow, when the patient attempts to make a fist. Due to loss...

Epidemic typhus is a severe rickettsial disease caused by Rickettsia prowazekii, transmitted by the human body louse (Pediculus humanus corporis). It presents with high fever, severe headache, myalgias, and a centrifugal maculopapular/pe...

Endemic (murine) typhus is a febrile illness caused by Rickettsia typhi, transmitted via flea feces (Xenopsylla cheopis) from rats to humans. It presents with fever, headache, and a centrifugal maculopapular rash, and is typically milder...

Rhabdoviridae is a family of bullet-shaped, enveloped, negative-sense single-stranded RNA viruses, the most clinically important member being Rabies virus. It causes rabies, a near-universally fatal encephalitis transmitted via animal bi...

N protein (nucleocapsid protein) is a structural protein found in many RNA viruses, including coronaviruses, paramyxoviruses, and rhabdoviruses (e.g., rabies). It binds and encapsidates the viral genomic RNA, protecting it and forming th...

NSP4 (Non-Structural Protein 4) is a rotavirus enterotoxin that plays a central role in the pathogenesis of rotavirus-induced diarrhea, the leading cause of severe gastroenteritis in infants and young children worldwide. It acts as a vir...

Acute megakaryoblastic leukemia (AML-M7, FAB classification) is a rare subtype of acute myeloid leukemia characterized by proliferation of malignant megakaryoblasts. It is strongly associated with Down syndrome (children <3 years old) an...

Acute monocytic leukemia (AML FAB M5) is a subtype of acute myeloid leukemia characterized by proliferation of monoblasts/monocytes, often associated with gum infiltration, skin involvement, and extramedullary (soft tissue) masses. It is...

Helminths are multicellular parasitic worms, classified into three main groups: nematodes (roundworms), cestodes (tapeworms), and trematodes (flukes). They cause significant global disease burden, often via fecal-oral transmission, skin...

Tazobactam is a beta-lactamase inhibitor combined with piperacillin to extend its antibacterial spectrum. It irreversibly inhibits many bacterial beta-lactamase enzymes, protecting piperacillin from degradation. It has no significant int...

Bortezomib is a first-in-class proteasome inhibitor used primarily to treat multiple myeloma and mantle cell lymphoma. It works by inhibiting the 26S proteasome, leading to accumulation of pro-apoptotic factors and cell cycle regulators,...

Andexanet alfa is a recombinant modified factor Xa decoy protein used as a reversal agent for bleeding associated with the factor Xa inhibitors apixaban and rivaroxaban. It works by binding and sequestering these anticoagulants, restorin...

Piperacillin is an extended-spectrum (antipseudomonal) penicillin, typically combined with the beta-lactamase inhibitor tazobactam, used to treat serious infections including those caused by Pseudomonas aeruginosa, gram-negative rods, an...

Argatroban is a direct thrombin inhibitor (DTI) used as an anticoagulant, most notably in patients with heparin-induced thrombocytopenia (HIT). It binds directly to the active site of thrombin (factor IIa), inhibiting both free and clot-...

Idarucizumab is a humanized monoclonal antibody fragment that serves as a specific reversal agent for dabigatran, a direct thrombin inhibitor. It binds dabigatran with much higher affinity than dabigatran binds thrombin, rapidly neutrali...