Infectious and Systemic Disease of the GI Tract
Core concepts
Recognize infections by setting and presentation. Clostridioides difficile causes antibiotic-associated diarrhea; test only with symptoms, and treat with oral vancomycin or fidaxomicin for severe disease. Infectious esophagitis: Candida in immunocompromised, HSV with ulcers, CMV with large ulcers. GI tuberculosis and histoplasmosis can mimic inflammatory bowel disease. Whipple disease causes malabsorption with arthralgias and neurologic findings.
Systemic disease affects the gut: scleroderma causes dysmotility, amyloid causes bleeding or obstruction, and vasculitis can cause ischemia. HIV-related GI disease includes opportunistic infections and medication effects. Parasites such as Giardia cause malabsorption and bloating; stool antigen or PCR helps.
Traps
Do not test for C difficile without diarrhea. Do not treat asymptomatic bacteriuria or colonization. Distinguish infectious colitis from IBD before starting steroids, which can worsen infection. Recognize that CMV colitis can complicate severe IBD and requires biopsy with viral staining.
Rule of thumb
In a patient with bloody diarrhea and recent antibiotics or hospitalization, test for C difficile and consider it before escalating immunosuppression for presumed IBD flare.