How can Brainerd diarrhea be diagnosed?

Because the etiologic agent is unknown, there is no laboratory test that can confirm the diagnosis. Brainerd diarrhea should be suspected in any patient who presents with the acute onset of nonbloody diarrhea lasting for more than 4 weeks, and for whom stool cultures and examinations for ova and parasites have been negative. Care should be taken to exclude other causes of chronic diarrhea, both infectious and noninfectious (e.g., lymphocytic colitis, collagenous colitis, tumors, drug reactions). Brainerd diarrhea is not characterized by any specific laboratory abnormalities. On colonoscopy, petechiae, aphthous ulcers and erythema may be observed. Microscopic examination of colonic tissue biopsy specimens often reveals mild inflammation, with an increased number of lymphocytes, particularly in the ascending and transverse colon. The stomach and small intestine generally appear normal.