Eosinophilic Colitis

Eosinophilic colitis is a rare eosinophilic gastrointestinal disorder with dense eosinophilic infiltration of the colonic wall and no secondary cause. It causes chronic diarrhoea and abdominal pain.

It has a bimodal age distribution: infants (often with food protein induced disease that resolves by age 1 to 2 years) and adults in the third to fifth decades. Associated atopy is present in up to half of patients, and the disease may relapse for years.

Pathophysiology.

Allergic type 2 inflammation recruits and activates eosinophils, whose granule proteins damage the mucosa and disrupt motility. The right colon is most often involved.

Chronic watery or bloody diarrhoea, abdominal pain, weight loss, protein losing enteropathy, anaemia and, in infants, blood in the stool and failure to thrive. Transmural disease causes obstruction, perforation or ascites.

Red flags.

• Peritonitis.
• Intestinal obstruction.
• Severe bleeding.
• Infant failure to thrive.

Colonoscopy with biopsies from all segments (right colon eosinophil counts are higher: diagnosis suggested by more than 100 eosinophils in each high power field in the caecum, 84 in the transverse colon and 64 in the left colon, with no agreed threshold). Exclude parasites (Strongyloides, Ascaris, Trichuris), drug reactions, inflammatory bowel disease, hypereosinophilic syndrome and eosinophilic granulomatosis with polyangiitis. Check blood eosinophils, stool microscopy and serology.

Differential diagnosis.

• Parasitic colitis.
• Ulcerative colitis and Crohn disease.
• Drug induced eosinophilic colitis.
• Hypereosinophilic syndrome.
• Microscopic colitis.
• Food protein induced allergic proctocolitis in infants.

Treat parasitic infection first if suspected. Try dietary elimination (cow's milk and maternal elimination in infants), then corticosteroids for symptomatic adults, with steroid sparing agents for relapse.

• Ivermectin (if Strongyloides cannot be excluded before steroids): 200 micrograms/kg orally once daily for 2 days; maximum 12 mg for each dose; monitor liver tests and for neurotoxicity; avoid in Loa loa co-infection.
• Prednisolone: 0.5 to 1 mg/kg orally once daily (maximum 40 mg daily) for 2 to 4 weeks, then taper over 4 to 8 weeks; monitor glucose, blood pressure and bone health; reduce in older adults and give gastric protection.
• Budesonide (ileocaecal release formulation): 9 mg orally once daily in the morning for 8 weeks, then 6 mg daily for 4 weeks and 3 mg daily; maximum 9 mg daily; monitor for adrenal suppression and infection; avoid in severe hepatic impairment.
• Azathioprine (steroid dependent disease): 2 to 2.5 mg/kg orally once daily; maximum 3 mg/kg daily; check thiopurine methyltransferase activity first, and monitor blood counts and liver tests every 2 weeks for 2 months, then every 3 months; reduce the dose in renal impairment and with allopurinol.

Monitoring. Symptoms, weight and blood eosinophils every 3 months; repeat colonoscopy and biopsies after treatment if symptoms persist.

Referral and escalation. Gastroenterology and allergy services; surgery for obstruction or perforation.

Special groups. Infants usually recover by 1 to 2 years with allergen elimination alone, using extensively hydrolysed or amino acid formula.