1. ¹Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, University of Toronto, Toronto, ON, Canada
2. ²Department of Pathology, University Hospital Leuven, Leuven, Belgium
3. ³Department of Histopathology, Gloucestershire Royal Hospital, Gloucester, UK
4. ⁴Cranfield Postgraduate Medical School in Gloucestershire, Gloucestershire Royal Hospital, Gloucester, UK
5. ⁵Department of Gastroenterology, Children's Hospital of Los Angeles, the Keck School of Medicine of University of Southern California, Los Angeles, CA, USA
6. ⁶National Center of Pathology, Vilnius, Lithuania

Correspondence: Dr R Kirsch, MBChB, PhD, FRCPC, Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, 600 University Avenue, Toronto, ON M5G 1X5, Canada. E-mail: rkirsch@mtsinai.on.ca

Received 15 April 2008; Revised 18 June 2008; Accepted 19 June 2008; Published online 17 October 2008.

Abstract

Systemic mastocytosis is an uncommon condition characterized by abnormal proliferation of mast cells in one or more organ. The specific D816V KIT mutation is present in most cases. Gastrointestinal symptoms occur commonly but histologic characterization of gastrointestinal involvement is incomplete. The purpose of this study was (1) to describe the clinicopathologic features in five patients with systemic mastocytosis involving the gastrointestinal tract and (2) to determine whether gastrointestinal involvement is associated with the usual D816V mutation or a different mutation. Clinical details were obtained from the hospital of origin or referring pathologist. Histologic features were documented in slides stained with hematoxylin and eosin, mast cell tryptase and CD117. Molecular analysis for the D816V KIT mutation was performed on formalin-fixed paraffin-embedded sections. Symptoms included diarrhea/loose stools (n=5), abdominal pain (n=4), vomiting (n=3) and weight loss (n=3). Other findings included cutaneous lesions of mastocytosis (n=4), malabsorption (n=2), hypoalbuminemia (n=2) and constitutional growth delay (n=1). Sites of gastrointestinal involvement included the colon (n=5), duodenum (n=3) and terminal ileum (n=3). Endoscopic/gross findings included mucosal nodularity (n=4), erosions (n=2) and loss of mucosal folds (n=2). In three patients the endoscopic appearance was considered consistent with inflammatory bowel disease. All cases showed increased mast cell infiltration of the lamina propria, confirmed by immunohistochemistry for mast cell tryptase and CD117. In two cases, mast cells had abundant clear cytoplasmic resembling histiocytes. Marked eosinophil infiltrates were present in four patients, in one patient leading to confusion with eosinophilic colitis. Architectural distortion was noted in three cases. The D816V KIT mutation was present in all four cases tested. In conclusion, gastrointestinal involvement by systemic mastocytosis is characterized by a spectrum of morphologic features that can be mistaken for inflammatory bowel disease, eosinophilic colitis or histiocytic infiltrates. Systemic mastocytosis involving the gastrointestinal tract is associated with the usual D816V KIT mutation.