1500+ medical terms, defined.

Chancroid is a sexually transmitted genital ulcer disease caused by Haemophilus ducreyi, characterized by painful, soft, ragged ulcers and tender suppurative inguinal lymphadenopathy. It is distinguished from the painless chancre of prim...

Cytomegalovirus is human herpesvirus 5, an enveloped double-stranded DNA virus that is usually asymptomatic in immunocompetent hosts but causes serious disease in neonates and the immunosuppressed. It produces characteristic 'owl's eye'...

Rhagades are linear scars radiating from the corners of the mouth, nose, and anus, produced by healing of the perioral inflammatory lesions of congenital syphilis. They are a late stigma of untreated congenital infection.

Hematogenous means spread through the bloodstream. It describes the route by which infections and metastatic tumours reach distant organs, in contrast to lymphatic, contiguous, or direct-inoculation spread.

Conjunctival suffusion is redness of the conjunctiva from dilated vessels without purulent discharge or exudate. It is a classic and relatively specific sign of leptospirosis.

Leptospirosis is a zoonotic spirochaetal infection caused by Leptospira interrogans, acquired through water contaminated with animal urine. It causes a biphasic illness of fever, myalgia, and conjunctival suffusion that may progress to W...

A louse is a wingless ectoparasitic insect that feeds on blood; human species are the head louse, body louse, and pubic louse. The body louse, Pediculus humanus corporis, is the vector for epidemic typhus, trench fever, and louse-borne r...

Erythema chronicum migrans is the expanding annular rash of early localized Lyme disease, often with central clearing producing a target or bull's-eye appearance. It appears days to a month after an Ixodes tick bite and is diagnostic eno...

Mycobacterium marinum is a slow-growing non-tuberculous mycobacterium acquired from aquariums, swimming pools, and fish handling that causes a granulomatous skin infection of the hands and arms. It classically produces nodules that ascen...

Mycobacterium scrofulaceum is a non-tuberculous mycobacterium that causes cervical lymphadenitis (scrofula) in young children, typically producing a painless, unilateral, enlarging neck mass. Treatment is surgical excision rather than an...

Mycobacterium intracellulare is, with Mycobacterium avium, one of the two organisms of Mycobacterium avium complex (MAC). It causes chronic pulmonary disease in patients with structural lung disease and disseminated infection when the CD...

Combination antiretroviral therapy is the use of at least three active antiretroviral drugs from two or more classes to suppress HIV replication. Combination is essential because monotherapy invariably selects resistance given the error-...

Lepromatous leprosy is the diffuse, multibacillary form of Hansen disease resulting from a weak Th1 and predominant Th2 response to Mycobacterium leprae. It causes symmetric skin lesions, leonine facies, and glove-and-stocking neuropathy...

Lymphangitis is inflammation of lymphatic channels, typically appearing as tender red streaks tracking proximally from a site of infection toward regional nodes. Acute bacterial lymphangitis is most often caused by Streptococcus pyogenes.

Oxygen tension is the partial pressure of oxygen dissolved in a gas or fluid, written PO2 and measured in mmHg. It is the driving force for oxygen diffusion and is distinct from oxygen content, which is dominated by haemoglobin-bound oxy...

The Ghon complex is the combination of a subpleural parenchymal granuloma (Ghon focus) with involvement of the draining hilar lymph nodes, formed during primary tuberculosis. When it calcifies and fibroses it is called a Ranke complex.

Carbol fuchsin is the primary red dye of the Ziehl-Neelsen acid-fast stain, retained by organisms whose mycolic acid-rich cell walls resist decolorization with acid-alcohol. Acid-fast bacilli appear red against a blue methylene blue coun...

Miliary tuberculosis is widespread haematogenous dissemination of Mycobacterium tuberculosis producing innumerable small granulomas throughout the lungs and other organs. The chest radiograph shows a diffuse pattern of tiny nodules resem...

Mycolic acids are very long-chain branched fatty acids that make up the waxy outer layer of the mycobacterial cell wall. They confer acid-fastness, resistance to desiccation and disinfectants, and slow growth, and their synthesis is the...

Undulant fever is the characteristic relapsing, rising-and-falling fever pattern of brucellosis. It is acquired from unpasteurized dairy products or contact with infected livestock and is accompanied by drenching sweats, myalgia, and art...

The deerfly (Chrysops species) is a biting fly that transmits Francisella tularensis, the agent of tularaemia, and Loa loa, the African eye worm. Deerfly bite is one of several routes by which tularaemia is acquired.

Dermacentor is a hard tick genus, including the American dog tick and Rocky Mountain wood tick, that transmits Rickettsia rickettsii, Francisella tularensis, and Colorado tick fever virus. It also causes tick paralysis through a neurotox...

The reticuloendothelial system, now more properly called the mononuclear phagocyte system, is the network of tissue macrophages derived from monocytes that filter blood and lymph and phagocytose pathogens, debris, and senescent cells. It...

The Warthin-Starry stain is a silver impregnation technique that renders thin, poorly staining bacteria black against a golden background. It is used to demonstrate spirochaetes, Bartonella henselae, Helicobacter pylori, and the agent of...

Burkholderia pseudomallei is a gram-negative soil and water saprophyte of Southeast Asia and northern Australia that causes melioidosis. It produces abscesses in lung, liver, spleen, and skin, and can reactivate years after exposure, ear...

Convalescent describes the recovery phase of an illness, after the peak of symptoms and before full return to health. In pertussis it names the third stage, in which the paroxysmal cough gradually diminishes over weeks to months.

Paroxysmal means occurring in sudden, recurrent, self-limited attacks with return to baseline between episodes. It describes the second stage of pertussis and many episodic conditions across medicine.

Catarrhal refers to inflammation of a mucous membrane with profuse mucus production. It names the first stage of pertussis, which resembles a common cold, is the most contagious period, and is the only stage in which antibiotics shorten...

Rationalization is an immature ego defence mechanism in which a person invents an acceptable but false explanation to justify unacceptable feelings or behaviour. It differs from intellectualization, which avoids emotion by focusing on fa...

A watershed area is a border zone supplied by the most distal branches of two arterial territories, making it the first region to become ischaemic when perfusion falls. In the colon the classic watershed points are the splenic flexure (G...

Watershed areas of the colon are the border zones where one major artery's territory ends and the next begins, supplied only by fine terminal branches and therefore first to become ischaemic. The two classic colonic points are the spleni...

Cooper's ligament most often means the pectineal ligament, a strong fibrous band along the pectineal line of the superior pubic ramus, lying deep and inferior to the inguinal ligament and used as an anchor in hernia repair. The same name...

Pyocyanin is a blue-green phenazine pigment produced by Pseudomonas aeruginosa that gives its colonies and infected exudate a characteristic colour. It is a virulence factor that generates reactive oxygen species and damages host tissue.

Legionella pneumophila is a facultative intracellular gram-negative rod transmitted by inhaling aerosols from contaminated water systems. It causes Legionnaires disease, a severe atypical pneumonia often accompanied by diarrhoea, confusi...

Coccidioides immitis and posadasii are dimorphic fungi endemic to the south-western United States that cause coccidioidomycosis, or valley fever. In tissue they form large spherules packed with endospores, which is diagnostic.

Facultative intracellular organisms can survive and replicate inside host cells, particularly macrophages, but are also able to grow extracellularly and on artificial media. Their intracellular niche means control depends on cell-mediate...

A zoonotic infection is one transmitted from vertebrate animals to humans, either directly, through animal products, or via an arthropod vector. Identifying the animal exposure is often the fastest route to the diagnosis.

Francisella tularensis is a highly infectious, facultative intracellular gram-negative coccobacillus causing tularaemia, acquired from rabbits, ticks, and deerflies. As few as ten organisms can cause disease, making it a category A biote...

Brucella species are small, aerobic, facultative intracellular gram-negative coccobacilli acquired from unpasteurized dairy products or livestock contact. They cause brucellosis, characterized by undulant fever, drenching sweats, and ost...

A bubo is a markedly swollen, exquisitely tender lymph node, classically in the groin, axilla, or neck. Buboes are the defining feature of bubonic plague and also occur in chancroid, lymphogranuloma venereum, and tularaemia.

The type III secretion system is a needle-like molecular syringe used by gram-negative bacteria to inject effector proteins directly from their cytoplasm into a host cell. It is often called the injectisome and is a key virulence determi...

Dicyclomine is an antimuscarinic antispasmodic used to relieve intestinal smooth muscle spasm, chiefly in irritable bowel syndrome. Its adverse effects are the predictable anticholinergic set: dry mouth, blurred vision, constipation, and...

Hyoscyamine is the levorotatory isomer of atropine, a naturally occurring belladonna alkaloid used as an antimuscarinic antispasmodic. It reduces gastrointestinal and urinary smooth muscle tone and secretions.

Antispasmodics are drugs that relieve smooth muscle spasm of the gut, chiefly antimuscarinics such as dicyclomine and hyoscyamine and direct smooth muscle relaxants such as peppermint oil. They are used for the cramping abdominal pain of...

Xerostomia is dry mouth from reduced salivary flow. The commonest cause is medication with anticholinergic activity, and the most important disease cause is Sjogren syndrome.

Dyspepsia is chronic or recurrent upper abdominal pain or discomfort centred in the epigastrium, often with early satiety, bloating, or nausea. Most cases are functional, but alarm features require prompt endoscopy to exclude malignancy.

Serratia marcescens is a motile, non-lactose-fermenting gram-negative rod of the Enterobacteriaceae that produces a red pigment, prodigiosin. It is an opportunistic nosocomial pathogen causing pneumonia, urinary tract infection, and bact...

Facultative describes an organism able to use an alternative mode of metabolism or lifestyle when conditions require. A facultative anaerobe can generate energy by aerobic respiration when oxygen is present and by fermentation or anaerob...

Tenosynovitis is inflammation of a tendon and its surrounding synovial sheath, producing pain on movement, swelling along the tendon, and tenderness. Infectious tenosynovitis of the flexor tendon sheath of the hand is a surgical emergency.

Cervicofacial actinomycosis is a chronic granulomatous infection of the jaw and neck caused by Actinomyces israelii, producing a firm, indurated mass with draining sinus tracts that discharge yellow sulfur granules. It is classically pre...