Microscopic Ischaemic Colitis

Microscopic ischaemic colitis is mild, non-gangrenous ischaemic injury to the colonic mucosa in which the changes are identified histologically (crypt atrophy, hyalinised lamina propria, mucosal necrosis, withered crypts) and endoscopic findings are minimal or patchy.

• It results from low flow states and small vessel disease rather than occlusion of a major artery, most often affecting the splenic flexure, descending colon and rectosigmoid (watershed areas).
• Risk factors: age above 60 years, hypotension, heart failure, atrial fibrillation, atherosclerosis, diabetes, chronic kidney disease, constipation, irritable bowel syndrome, vasculitis, hypercoagulable states, long distance running, and drugs (vasopressors, digoxin, oral contraceptives, ergotamine, alosetron, NSAIDs, cocaine, pseudoephedrine, chemotherapy).
• Most episodes resolve within 1 to 2 weeks without sequelae.

Sudden crampy left-sided abdominal pain, urgent bloody diarrhoea or maroon stool within 24 hours, tenderness over the affected segment, and low grade fever.

• Rectal sparing is typical; severe pain out of proportion to signs suggests mesenteric ischaemia.
• Differential diagnosis: infectious colitis, Clostridioides difficile colitis, inflammatory bowel disease, diverticulitis, microscopic (collagenous or lymphocytic) colitis, colorectal cancer, acute mesenteric ischaemia, radiation colitis, NSAID colopathy.
• Complications: gangrene and perforation (up to 10 to 20 percent of severe cases), stricture (weeks later), chronic segmental colitis, recurrent episodes, sepsis and death.

Full blood count, lactate, creatinine, electrolytes, C-reactive protein, stool culture and Clostridioides difficile testing.

• CT abdomen with intravenous contrast shows segmental wall thickening and thumbprinting; CT angiography if mesenteric ischaemia is suspected.
• Colonoscopy or flexible sigmoidoscopy within 48 hours with minimal insufflation: pale or cyanotic mucosa, petechiae, single-stripe sign, segmental ulceration; biopsy shows ischaemic changes.
• Echocardiogram, electrocardiogram and Holter monitor for atrial fibrillation and heart failure.

Supportive

• Admit if age over 70 years, severe pain, peritonism or raised lactate.
• Bowel rest, intravenous fluids (crystalloid, maintain mean arterial pressure above 65 mmHg), correct heart failure and arrhythmia, stop precipitating drugs, analgesia (avoid opioids that slow the bowel; use paracetamol 1 g every 6 hours, or low dose fentanyl for severe pain).

Pharmacological

• Antibiotics for moderate to severe disease or if bowel necrosis is suspected: ciprofloxacin 400 mg IV every 12 hours plus metronidazole 500 mg IV every 8 hours, or ceftriaxone 2 g IV daily plus metronidazole 500 mg IV every 8 hours, for 5 to 7 days.
• Anticoagulation only for proven mesenteric venous thrombosis or embolic source: unfractionated heparin infusion (80 units/kg bolus then 18 units/kg/h, titrated) or enoxaparin 1 mg/kg twice daily, then warfarin.
• Mild disease: oral rehydration and liquid diet.

Procedures: surgical resection of gangrenous or perforated bowel for peritonitis, deterioration, massive bleeding or persistent symptoms after 2 to 3 weeks; endoscopic dilatation or segmental resection for symptomatic stricture; revascularisation if superior mesenteric artery stenosis.

Special groups: elderly with heart failure (cautious fluids), dialysis patients (haemodynamic stability during sessions), young athletes (hydration and training modification).

Red flags: peritonism, lactate above 2 mmol/L, falling blood pressure, right-sided or pancolonic involvement, gangrene on endoscopy (black mucosa), pneumatosis or portal venous gas on CT.

Follow-up: repeat colonoscopy at 6 to 8 weeks to confirm healing and exclude stricture or neoplasia; screen for atrial fibrillation and optimise cardiovascular risk (statin, antihypertensive, glycaemic control).