Answer: Histoplasmosis

Histology: This is from an adhesed segment of small bowel. The bowel was involved by a transmural necrotizing granulomatous process. There are extensive areas of geographic necrosis composed of cellular debris, and on closer inspection fine, blue particles are identified. These budding yeast forms are highlighted on GMS stain.

Discussion: Crohn’s disease is a transmural granulomatous process of the bowel, but the granulomas typically lack necrosis. Indeterminant Colitis is used for a colitis with features of both Ulcerative Colitis and Crohn’s disease where a definitive distinction cannot be made. In this case, there is almost nothing to suggest Ulcerative Colitis. A small bowel lymphoma could be characterized by extensive areas of necrosis; however, the large atypical lymphoid cells that one would expect to see are not present in this case.

Histoplasmosis is endemic in the Mississippi and Ohio valleys of the United States. Over 90% of infected patients are asymptomatic, as they develop some cell-mediated immunity, and form granulomas that undergo calcification and fibrosis. Five to 10% of patients become symptomatic in one of three ways: an acute pulmonary form that produces flu-like symptoms for approximately two weeks, a disseminated form that extensively involves the reticuloendothelial system in immunosuppressed hosts, and a chronic pulmonary form that is similar to reactivation tuberculosis.

In the bowel, the granulomas of a case of suspected Crohn’s disease should probably be stained at least once for fungus and acid-fast bacilli. There seems to now be an association of Disseminated Histoplasmosis with anti-TNF-á (tumor necrosis factor) therapy, such as Remicade.

Reference(s):
– Am J Respir Crit Care Med 2003;167: 1279-1282.