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IM16.{1-3,6,15} | Diarrheal Disorder Foundations — SDL Guide (Part 3)
Self-Assessment: Integrating Diarrhoeal Disorder Foundations
You have now covered the full foundational scope of diarrhoeal disorders: classification by duration (acute/persistent/chronic), the four pathophysiological mechanisms (secretory/osmotic/inflammatory/malabsorptive), the clinical distinction between diarrhoea and dysentery, the acute systemic consequences of dehydration with the WHO Plan A/B/C framework and ORS composition, the chronic consequences of malabsorptive diarrhoea, and the distinguishing features of Crohn's disease versus ulcerative colitis. The scenarios below test your integration across these domains — work through each before reading the analysis.
Scenario A: A 55-year-old woman presents with a 6-month history of foul-smelling, floating, pale stools, 5 kg weight loss, abdominal bloating, and angular stomatitis. She denies blood in stool or fever. Her Hb is 9.2 g/dL (microcytic), serum albumin 2.8 g/dL, INR 1.6, and Vitamin D 18 ng/mL (deficient). What mechanism is operative, and which investigations would you prioritise?
Analysis: Pale floating stools = steatorrhoea. The multi-nutrient deficiency picture (iron-deficient anaemia, hypoalbuminaemia, prolonged INR from vitamin K deficiency, vitamin D deficiency) confirms malabsorptive diarrhoea. The combination of these deficiencies localises the problem to the small intestine (coeliac disease, tropical sprue). Prioritise: anti-tTG IgA + serum total IgA (for coeliac, to rule out IgA deficiency that would falsely normalise), upper GI endoscopy with duodenal biopsy (villous atrophy), and small bowel imaging if Crohn's ileitis is possible. Haematinics (serum B12, folate, ferritin) and a 72-hour faecal fat collection confirm the malabsorption.
Scenario B: A 22-year-old man has frequent small-volume bloody mucoid stools with tenesmus and fever for 10 days. He recently returned from a week-long rural camp. Stool microscopy shows trophozoites with ingested red blood cells. His fever is 38.2°C, no peritoneal signs, and abdominal ultrasound shows no hepatic lesions. What is the diagnosis, and what is the complete treatment course?
Analysis: Trophozoites with phagocytosed red blood cells = Entamoeba histolytica trophozoites — pathognomonic. This is intestinal amoebiasis (no liver abscess on ultrasound). The clinical picture is dysentery (bloody mucoid stools, tenesmus, fever). Treatment: metronidazole 400–800 mg TDS × 10 days (tissue amoebicide to kill invasive trophozoites) FOLLOWED BY diloxanide furoate 500 mg TDS × 10 days (luminal amoebicide to eradicate cysts and prevent relapse or transmission). This two-drug sequential approach is mandatory — treating with metronidazole alone leaves luminal cysts that can cause recurrence.
Scenario C: During a medical camp after flooding in coastal Odisha, you encounter five patients from the same village with acute onset of profuse watery stools over 6 hours. Two patients have sunken eyes and are drinking eagerly but have normal skin pinch. Three patients have altered sensorium and very slow skin pinch. How do you classify and prioritise these patients for treatment?
Analysis: Two patients = Plan B (some dehydration) — two clinical signs (sunken eyes + drinks eagerly). Treatment: supervised ORS 75 mL/kg WHO low-osmolarity ORS (osmolarity 245 mOsm/L) over 4 hours in a health facility. Three patients = Plan C (severe dehydration) — sunken eyes + impaired consciousness + very slow skin pinch. Treatment: immediate IV Ringer's Lactate 100 mL/kg (first 30 mL/kg in 30 min, then 70 mL/kg over 2.5 hrs) + switch to ORS when alert. In suspected cholera outbreak: single-dose doxycycline 300 mg (adults) after rehydration.
SELF-CHECK
A 19-year-old woman with a 3-month history of bloody diarrhoea and rectal urgency undergoes colonoscopy, which shows continuous mucosal inflammation from the rectum extending to the splenic flexure, with no skip lesions and no small bowel involvement. Biopsy shows crypt abscesses and goblet cell depletion. Which diagnosis is CORRECT, and which INITIAL pharmacotherapy is most appropriate?
A. Crohn's disease; metronidazole for perianal fistula
B. Ulcerative colitis; mesalamine (5-aminosalicylic acid)
C. Crohn's disease; infliximab (anti-TNF)
D. Ulcerative colitis; total colectomy
Reveal Answer
Answer: B. Ulcerative colitis; mesalamine (5-aminosalicylic acid)
Continuous mucosal-only inflammation from the rectum without skip lesions, confined to the colon — this is classic ulcerative colitis (UC). Crypt abscesses and goblet cell depletion are the histological hallmarks of UC. Crohn's disease would show transmural inflammation, skip lesions, granulomas, and commonly small bowel involvement. For mild-to-moderate UC, first-line pharmacotherapy is mesalamine (5-aminosalicylate / 5-ASA) — both oral (sulfasalazine or mesalamine tablets) and rectal (suppository, enema) formulations are used depending on disease extent. Anti-TNF (infliximab) is reserved for moderate-severe refractory disease. Total colectomy is curative but reserved for toxic megacolon, dysplasia, or medically refractory disease — not initial therapy.
CLINICAL PEARL
The sodium-glucose co-transporter mechanism (SGLT1) that makes oral rehydration therapy effective is not inhibited by cholera toxin — cholera toxin acts on CFTR chloride channels, not SGLT1. This is why WHO ORS, which pairs glucose with sodium in a 1:1 molar ratio, can reverse even severe cholera dehydration from the gut lumen itself. The counterintuitive fact is that a patient pouring out 500 mL of rice-water stool per hour can be rehydrated by mouth, provided they can tolerate fluid intake. This principle — discovered in the 1960s from studies on cholera patients in Dhaka — has been called 'the most important medical advance of the 20th century' in developing-world medicine.
A second pearl: in a patient with suspected Crohn's disease in India, always exclude intestinal tuberculosis before starting immunosuppressants. The clinical, endoscopic, and radiological overlap is substantial (ileocaecal involvement, strictures, granulomas). TB granulomas are caseating; Crohn's granulomas are non-caseating — but the distinction requires adequate biopsy depth and is not always reliable. In endemic India, a 2-month empirical anti-TB trial is often appropriate before committing to immunosuppressive therapy for 'IBD'.