We present the case of a man in his 70s who was referred to gastroenterology with several months’ history of offensive smelling loose stools and weight loss. He underwent a standard panel of initial investigations including colonoscopy for his chronic diarrhoea. Colonoscopy was reported as normal and the results of the rest of his screening panel were unremarkable. As his symptoms persisted, lower GI endoscopy was repeated. This showed a few scattered diverticula and some possible left colonic mucosal congestion, but biopsies were reported as within normal limits (see figure 1).

H&E stain of colonic biopsy.

Concurrently, the patient started developing exertional breathlessness. Blood tests did not reveal any …