Cytomegalovirus Colitis

Cytomegalovirus colitis is colonic infection by cytomegalovirus, causing ulceration, bleeding and, occasionally, toxic dilatation or perforation. It is the commonest gastrointestinal site of cytomegalovirus disease.

It occurs in transplant recipients, advanced HIV infection, malignancy on chemotherapy and critical illness. It also complicates severe, steroid refractory ulcerative colitis, where reactivation is found in up to 30% of such cases and is an adverse factor for outcome.

Pathophysiology.

Reactivation in the colonic endothelium and stromal cells causes vasculitis, mucosal ischaemia and deep ulceration. Inflammation of the mucosa in ulcerative colitis promotes local reactivation.

Bloody or watery diarrhoea, abdominal pain, urgency, fever, weight loss and anaemia. Complications are toxic megacolon, perforation and massive bleeding. In ulcerative colitis, failure of corticosteroid or biologic therapy is the usual clue.

Red flags.

• Toxic megacolon (colonic diameter over 6 cm with toxicity).
• Peritonitis.
• Massive haemorrhage.
• Fever with hypotension.

Colonoscopy or flexible sigmoidoscopy shows deep, well demarcated, punched out or linear ulcers, with erythema and erosions, often in the right colon or rectum. Biopsy ulcer edge and base for haematoxylin eosin ("owl's eye") and cytomegalovirus immunohistochemistry. Blood PCR supports the diagnosis. Exclude Clostridioides difficile and other pathogens in stool. Check full blood count, C-reactive protein, albumin and CD4 count in HIV. Abdominal radiograph or CT for dilatation.

Differential diagnosis.

• Ulcerative colitis flare without virus.
• Crohn disease.
• Clostridioides difficile colitis.
• Ischaemic colitis.
• Graft-versus-host disease.
• Other infective colitis.

Start antiviral therapy, treat the underlying disease and optimise immunosuppression.

• Ganciclovir: 5 mg/kg IV every 12 hours for 2 to 3 weeks; maximum 10 mg/kg daily; monitor full blood count twice weekly and renal function; adjust by creatinine clearance: 50 to 69 mL/min 2.5 mg/kg every 12 hours; 25 to 49 mL/min 2.5 mg/kg every 24 hours; 10 to 24 mL/min 1.25 mg/kg every 24 hours; under 10 mL/min 1.25 mg/kg three times weekly after dialysis; withhold when neutrophils are under 0.5 x 10^9/L or platelets are under 25 x 10^9/L.
• Valganciclovir (when oral absorption is reliable and disease is mild to moderate): 900 mg orally twice daily with food; 2 to 3 weeks; maximum 1,800 mg daily; monitor counts and creatinine; reduce to 450 mg twice daily for creatinine clearance 40 to 59 mL/min, 450 mg once daily for 25 to 39 mL/min and 450 mg every 2 days for 10 to 24 mL/min.
• Foscarnet (resistance or marrow suppression): 90 mg/kg IV every 12 hours for 2 to 3 weeks with saline loading; maximum 180 mg/kg daily; monitor creatinine, calcium, magnesium, potassium and phosphate; reduce stepwise by creatinine clearance.

In ulcerative colitis, reduce or stop thiopurines and anti-tumour necrosis factor agents where feasible, but continue effective immunosuppression in severe disease because antivirals alone often fail. Colectomy is required for toxic megacolon, perforation, massive bleeding or refractory disease. Start antiretroviral therapy in HIV.

Monitoring. Viral load weekly, blood counts twice weekly, renal function, stool frequency, and repeat endoscopy at 2 to 3 weeks if not improving.

Referral and escalation. Gastroenterology and infectious diseases; colorectal surgery for severe or refractory colitis.