IM16.1-17 | Diarrheal Disorders — Glossary

5-aminosalicylic acid; first-line maintenance and active treatment for mild-to-moderate UC; acts locally in colonic mucosa to reduce inflammation via inhibition of prostaglandin synthesis and NF-κB; formulations include sulfasalazine (with sulfapyridine carrier — more side effects) and mesalamine (5-ASA only — preferred).

A quantitative test for fat malabsorption; the patient consumes a standardised 100 g/day fat diet for 3 days; total stool fat is measured; >7 g/day indicates fat malabsorption (steatorrhoea); >14 g/day = significant malabsorption.

Diarrhoeal illness lasting less than 2 weeks; predominantly infectious aetiology; most episodes self-resolve within 3–5 days.

A complication of invasive Entamoeba histolytica infection in which amoebae spread via the portal circulation to the liver, forming a large cavity filled with 'anchovy-sauce' pus; presents with fever, right hypochondrial tenderness, hepatomegaly, and intercostal tenderness; diagnosed by ultrasound; treated with metronidazole.

The first-line serological test for coeliac disease; sensitivity ~97%, specificity >95% in patients with normal serum IgA; measures IgA antibodies against tissue transglutaminase 2 (tTG2), the autoantigen in coeliac disease.

Monoclonal antibodies targeting tumour necrosis factor alpha; infliximab (IV) and adalimumab (SC) are the licensed agents in IBD; indications: moderate-severe UC/CD refractory to immunomodulators; mandatory TB screening before starting (reactivation risk); risk of serious infections and lymphoma.

Thiopurine immunomodulatory drugs used for maintenance of remission in IBD; azathioprine is metabolised to 6-MP (active moiety); inhibit purine synthesis and lymphocyte proliferation; dose: azathioprine 2–2.5 mg/kg/day, 6-MP 1–1.5 mg/kg/day; TPMT activity must be checked before starting; bone marrow suppression is the major toxicity.

Enzyme immunoassay (EIA) or NAAT/PCR detecting C. difficile toxins A and B or the organism's glutamate dehydrogenase (GDH); the appropriate test for post-antibiotic colitis; standard stool cultures do not reliably detect C. difficile and should NOT be ordered for this indication.

A glycoprotein tumour marker associated with colorectal carcinoma; elevated in approximately 60–70% of colorectal cancers; not sensitive or specific enough for diagnosis; useful for post-treatment monitoring and detecting recurrence.

A protein toxin of Vibrio cholerae that ADP-ribosylates the Gs-alpha subunit of adenylate cyclase, constitutively activating it to produce massive intracellular cAMP; drives CFTR-mediated chloride and water secretion.

Diarrhoeal illness lasting more than 4 weeks; predominantly non-infectious causes including IBD, malabsorption, functional disorders, and secretory tumours.

An anaerobic spore-forming bacterium producing toxins A and B that cause colitis; associated with recent broad-spectrum antibiotic use (especially clindamycin, fluoroquinolones, cephalosporins); presents with watery to bloody diarrhoea, fever, and lower abdominal pain; diagnosis: stool GDH + toxin ELISA or PCR.

A chronic inflammatory bowel disease characterised by transmural, skip-lesion inflammation that can involve any segment of the GI tract from mouth to anus; associated with non-caseating granulomas, fistulae, and perianal disease.

Collections of neutrophils within intestinal crypts visible on histology; a hallmark of ulcerative colitis; also seen in infectious colitis but persistent crypt abscesses in the clinical context of chronic IBD are diagnostic.

An intracellular protozoan parasite causing self-limiting watery diarrhoea in immunocompetent individuals; in HIV patients with CD4 <200 cells/μL, it causes severe chronic diarrhoea that is life-threatening; diagnosed by modified Ziehl-Neelsen stain on stool; treatment in HIV = ART to restore immunity.

A cross-sectional imaging technique using CT with oral neutral contrast (typically water) to optimally distend and visualise the small bowel; used for assessing Crohn's disease extent, strictures, fistulae, and mesenteric involvement.

The characteristic rapid, straight-line shooting movement of Vibrio cholerae on hanging-drop preparation, driven by its single polar flagellum; distinguishes V. cholerae from other bacteria and intestinal organisms; used for presumptive diagnosis in district hospitals and outbreak settings before culture confirmation.

Passage of ≥3 loose or liquid stools per day, or stool weight >200 g/day, representing a change from baseline bowel habit.

Palpation of the rectal ampulla and surrounding structures through the anal canal using a lubricated, gloved index finger; detects rectal masses, tenderness, blood/mucus, and anal sphincter tone; essential in any patient with chronic diarrhoea, rectal bleeding, or suspected colorectal malignancy.

A luminal amoebicide used after metronidazole (tissue amoebicide) in amoebiasis treatment; eradicates intraluminal cysts to prevent recurrence and transmission; dose 500 mg TDS × 10 days.

An aversive reaction to alcohol in the presence of drugs that inhibit aldehyde dehydrogenase (e.g., metronidazole, tinidazole); acetaldehyde accumulates, causing flushing, nausea, vomiting, and palpitations; patients taking metronidazole must strictly avoid alcohol during treatment and for 48 hours after completion.

Histological assessment of duodenal mucosal architecture for coeliac disease diagnosis; Marsh 0 = normal; Marsh 1 = increased intraepithelial lymphocytes; Marsh 2 = crypt hyperplasia; Marsh 3a/b/c = partial/subtotal/total villous atrophy — diagnostic of active coeliac disease.

Diarrhoea with visible blood and/or mucus in the stool, indicating mucosal invasion or inflammation; a distinct clinical entity from watery diarrhoea.

An intestinal protozoan parasite causing amoebiasis; trophozoites invade the colonic mucosa producing flask-shaped ulcers and bloody diarrhoea; trophozoites with ingested red blood cells on stool microscopy are pathognomonic.

Painful, indurated, erythematous nodules typically over the anterior shins; a non-specific extraintestinal manifestation seen in IBD (more common with Crohn's disease), sarcoidosis, TB, streptococcal infection, and drug reactions.

Engulfment of intact red blood cells by a phagocytic cell; in the context of stool microscopy, pathognomonic for Entamoeba histolytica trophozoites — no other intestinal protozoan ingests intact erythrocytes.

A protein released by neutrophils in inflamed intestinal mucosa; measured in stool; elevated in IBD and infectious enteritis; low (<50 µg/g) effectively excludes significant intestinal inflammation and supports IBS diagnosis; used to triage patients for colonoscopy.

White blood cells visible on stool microscopy; their presence indicates mucosal inflammation or invasion (invasive bacterial diarrhoea, IBD); their absence in watery diarrhoea suggests secretory or osmotic mechanism without mucosal invasion.

Transfer of stool from a healthy donor into the GI tract of a recipient to restore the disrupted gut microbiome; approved indication: recurrent C. difficile infection (90% cure rate for recurrent disease); investigational in UC, CD, and other microbiome-associated conditions.

The infective stage of Giardia intestinalis; oval, 8–19 µm, with 4 nuclei and visible median bodies on iodine staining; found in formed stool; intermittently excreted — three separate stool samples on different days achieve ~90% sensitivity.

The motile, pathogenic stage of Giardia intestinalis; pear-shaped (pyriform), bilaterally symmetrical, 10–20 µm long; two nuclei giving an 'owl-eye' appearance; four pairs of flagella; ventral adhesive disc; characteristic 'tumbling' or 'falling-leaf' motility on fresh wet preparation.

Passage of bright red or maroon blood per rectum; indicates lower GI bleeding or rapid upper GI bleeding; when seen with mucus in diarrhoeal context = dysentery.

A microangiopathic complication of STEC (Shiga toxin-producing E. coli) infection characterised by the triad: haemolytic anaemia (fragmented RBCs), thrombocytopaenia, and acute kidney injury; primarily affects children; management is supportive — avoid antibiotics and antimotility agents.

A microbiological technique for demonstrating bacterial motility in a fresh liquid specimen; a drop of specimen is placed on a coverslip and suspended over a hollow-ground slide, allowing direct microscopic observation of living organisms.

A non-invasive test for carbohydrate malabsorption (lactose, fructose) or small intestinal bacterial overgrowth (SIBO); after ingestion of a substrate, exhaled hydrogen is measured; a rise >20 ppm above baseline indicates colonic fermentation of unabsorbed carbohydrate.

An ileal reservoir constructed from a loop of terminal ileum folded on itself to create a J-shape; connected to the dentate line of the anus after proctocolectomy in UC; stores faecal material and allows near-normal defaecation; avoids a permanent ileostomy.

Diarrhoea resulting from mucosal invasion or immune-mediated inflammation, causing loss of blood, pus, and mucus into the stool; associated with fever, pain, tenesmus, and faecal leucocytes.

An antiparasitic drug (macrocyclic lactone class) used for strongyloidiasis (Strongyloides stercoralis); mechanism: binds glutamate-gated chloride channels in invertebrate neurons/muscle causing paralysis; dose 200 µg/kg/day × 2 days for intestinal strongyloidiasis; drug of choice, superior to albendazole for this indication.

A sexually transmitted infection caused by Chlamydia trachomatis serovars L1–L3; causes severe granulomatous proctitis in MSM; presents with bloody rectal discharge, pain, and tenesmus; requires 3 weeks of doxycycline (longer than standard chlamydia regimen).

Diarrhoea resulting from failure to absorb nutrients in the small intestine; characterised by steatorrhoea (pale, floating, foul-smelling fatty stools), multi-nutrient deficiencies, and chronic weight loss.

A form of chronic colitis with normal colonoscopic appearance but histological inflammation; two subtypes: collagenous colitis (thickened subepithelial collagen band >10 µm) and lymphocytic colitis (>20 intraepithelial lymphocytes per 100 epithelial cells); associated with NSAIDs, SSRIs, and PPIs; presents as chronic watery non-bloody diarrhoea.

An acid-fast staining technique using weaker acid decolorisation (1% H₂SO₄ rather than 3%); used to identify partially acid-fast organisms including Cryptosporidium parvum, Cyclospora cayetanensis, and Cystoisospora belli as pink/red oocysts against a blue background.

Diarrhoea that wakes the patient from sleep; indicates organic disease (IBD, microscopic colitis, secretory tumour, diabetic autonomic neuropathy); IBS classically does NOT cause nocturnal diarrhoea — its absence is a useful pointer toward functional disorder.

Epithelioid granulomas without central caseous necrosis; present in about 60% of Crohn's disease biopsies; the most specific histological finding when present; contrast with TB granulomas which are caseating.

The use of WHO low-osmolarity ORS (245 mOsm/L) to replace fluid and electrolytes lost in diarrhoea via the SGLT1 co-transporter mechanism; the primary treatment for Plan A and Plan B dehydration; effective even in severe cholera as long as the patient can drink.

A drop in systolic BP ≥20 mmHg or diastolic BP ≥10 mmHg on standing from a lying/sitting position; indicates significant intravascular volume depletion; correlates with Plan B-C dehydration in diarrhoeal disease.

Diarrhoea caused by a non-absorbable solute retaining water in the intestinal lumen; stops with fasting; high osmotic gap (>125 mOsm/kg); examples: lactase deficiency, lactulose, magnesium antacids.

A poorly absorbed aminoglycoside antibiotic used as a luminal amoebicide; alternative to diloxanide furoate; safe in pregnancy (unlike metronidazole which is relatively contraindicated in first trimester); also used for cutaneous leishmaniasis.

Diarrhoeal illness lasting 2–4 weeks; raises concern for parasitic infection, post-infectious mucosal disruption, or early chronic disease.

A crystalloid IV fluid containing Na 130, K 5.4, Ca 1.8, Cl 109, lactate 28 mEq/L; preferred over normal saline for severe dehydration in diarrhoeal disease because its lactate is metabolised to bicarbonate, partially correcting the associated metabolic acidosis.

Faint salmon-pink macular or papular lesions (2–4 mm) appearing in crops on the trunk and upper abdomen in approximately 10–20% of typhoid fever cases; caused by Salmonella typhi in dermal capillaries; transient (2–3 days); blanch on pressure.

Diarrhoea caused by cAMP/cGMP-mediated activation of CFTR channels driving net intestinal secretion; large-volume, watery, persists with fasting, low osmotic gap; prototype: cholera.

An intestinal epithelial transporter that co-transports one sodium and one glucose molecule into the enterocyte; not inhibited by cholera toxin; the mechanistic basis for oral rehydration therapy in secretory diarrhoea.

The elasticity of the skin, assessed by pinching a fold of skin (lateral abdomen in adults, subclavicular in children) and observing the time to return to flat; recoil >2 seconds indicates severe dehydration (Plan C); less reliable in elderly and obese patients.

Segmental, discontinuous areas of inflammation alternating with normal-appearing mucosa; a characteristic feature of Crohn's disease that distinguishes it from the continuous involvement of ulcerative colitis.

Presence of excess fat in stool (>7 g/day); stools appear pale, bulky, greasy, floating, and foul-smelling; indicates fat malabsorption (malabsorptive diarrhoea).

Calculated as measured/estimated stool osmolality − 2×(stool Na + stool K); <50 mOsm/kg indicates secretory diarrhoea; >125 mOsm/kg indicates osmotic diarrhoea.

A bowel-conserving surgical technique for Crohn's disease strictures; a longitudinal incision is made through the stricture and closed transversely, widening the lumen without intestinal resection; used to preserve intestinal length in patients with multiple strictures or prior resections at risk of short bowel syndrome.

A selective culture medium for Vibrio cholerae; the organism grows as large yellow colonies (sucrose-fermenting) within 24 hours; highly selective against most other enteric organisms.

The sensation of incomplete evacuation or rectal urgency with a feeling of needing to defaecate despite an empty or near-empty rectum; indicates rectal or distal colonic inflammation (dysentery, IBD proctitis, rectal carcinoma).

A drug that kills invasive E. histolytica trophozoites in the intestinal wall and liver; metronidazole and tinidazole are tissue amoebicides; they have limited luminal efficacy at standard doses — a separate luminal agent is always required after tissue treatment.

The standard surgical procedure for UC requiring colectomy; removes the entire colon and rectum; a J-shaped ileal reservoir (pouch) is created and anastomosed to the anus, preserving continence and avoiding a permanent ileostomy; potentially curative for UC.

Acute severe dilatation of the colon (transverse diameter >6 cm on abdominal X-ray) occurring as a complication of severe colitis (UC, Crohn's, C. diff, infectious colitis); presents with fever, tachycardia, abdominal distension, reduced bowel sounds, and rapid clinical deterioration; surgical emergency — risk of perforation.

An enzyme that metabolises 6-mercaptopurine (the active metabolite of azathioprine) via methylation; TPMT deficiency leads to accumulation of 6-MP and severe myelosuppression; TPMT activity must be measured before starting azathioprine; low activity = reduce dose or avoid; absent activity = contraindicated.

Diarrhoea occurring within 10 days of travel to a high-risk region (South Asia, sub-Saharan Africa, Southeast Asia, Latin America); predominantly caused by ETEC; self-limiting in 3–5 days; loperamide ± azithromycin for moderate cases.

A chronic inflammatory bowel disease restricted to the colon and rectum; inflammation is continuous from the rectum, mucosal and submucosal only; characterised histologically by crypt abscesses and goblet cell depletion.

A gut-selective anti-integrin biologic targeting α4β7, preventing lymphocyte trafficking to the GI mucosa; used in moderate-severe UC and CD refractory to anti-TNF or as first-line biologic where systemic immunosuppression is undesirable (older patients, high infection risk); lower systemic immunosuppression than anti-TNF.

WHO 2002 reduced-osmolarity oral rehydration solution: total 245 mOsm/L; Na 75 mEq/L, glucose 75 mmol/L, K 20 mEq/L, Cl 65 mEq/L, citrate 10 mmol/L; exploits SGLT1 co-transporter to drive coupled sodium-glucose-water absorption.

No dehydration management plan for diarrhoea: oral rehydration solution at home, increased fluids, continued feeding; no IV therapy required.

Some dehydration management plan: supervised ORS 75 mL/kg of WHO low-osmolarity ORS over 4 hours in a health facility; indicated by ≥2 of: restless, sunken eyes, thirsty, slow skin pinch.

Severe dehydration management plan: IV Ringer's Lactate 100 mL/kg (30 mL/kg in 30 min + 70 mL/kg over 2.5 hr); indicated by ≥2 of: lethargic/unconscious, very sunken eyes, unable to drink, very slow skin pinch (>2 sec).

An agglutination test measuring antibodies against Salmonella typhi O and H antigens; historically used for typhoid fever diagnosis; unreliable in endemic India due to background seropositivity, cross-reactions, and prior immunisation; blood culture is the gold standard.

WHO/UNICEF recommendation: 20 mg zinc/day × 10–14 days in children under 5 with acute diarrhoea; reduces duration and severity of the current episode and recurrence over the following 2–3 months; reflects endemic zinc deficiency in India impairing intestinal mucosal repair.