How would you manage a patient with Crohn's disease on a biologic and presents with non-bloody diarrhea, normal-appearing mucosa on sigmoidoscopy but severe colitis on biopsy with a positive CMV stain?

A few key pieces of information help distinguish CMV colitis from other competing diagnoses in this frequently encountered conundrum. An experienced pathologist will usually be able to tell you:

1. If the CMV immunohistochemistry stain has good controls and whether it is floridly positive or scant. Al...