Abstract
A 74-year-old man presented with a 2-month history of watery diarrhoea. His complete blood count showed lymphopaenia and marked eosinophilia. Investigations for common infectious causes including Clostridium difficile toxin, stool culture, ova and parasites were negative. Endoscopy revealed extensive colitis and a CT of the abdomen identified numerous large abdominal lymph nodes suspicious for lymphoma. Multiple tissue samples were obtained; colon, mesenteric lymph node and bone marrow biopsy, as well as pleural fluid from a rapidly developing effusion, confirmed the presence of metastatic lymphoma with an immunophenotype most consistent with an aggressive variant of Epstein-Barr virus (EBV)-negative natural killer (NK)-cell lymphoma. The patient's clinical condition rapidly deteriorated and he died shortly following diagnosis. To the best of our knowledge, this is the first case report of a primary gastrointestinal EBV-negative NK-cell lymphoma, and its clinical presentation highlights the importance of a broad differential in the management of chronic diarrhoea.