An unusual cause of intestinal failure.

A 62-year-old man presented to the emergency department with 5 weeks of worsening lower abdominal pain associated with watery diarrhoea, vomiting and 10% loss of body weight. He had recently experienced night blindness. There was no history of foreign travel. His past medical history included hypertension, sickle cell trait and type 2 diabetes well controlled on metformin. He had not been prescribed any recent steroids and denied significant alcohol intake. On examination, he had a tachycardia at 110 bpm and was afebrile and normotensive. He was malnourished with pedal pitting oedema extending to both knees. His abdomen was soft but distended and diffusely tender. Blood tests showed a serum albumin of 12 g/L. Stool samples were negative. HIV testing was negative, and immunoglobulin levels were normal. CT of the abdomen showed thickened, hyperenhancing jejunal loops with diffuse mesenteric inflammatory fat stranding and enlarged mesenteric lymph nodes. Colonoscopy was unremarkable. Enteroscopy showed granular oedematous mucosa and extensive, deep ulcerations. Jejunal biopsies were obtained. Microscopy samples were negative for tuberculosis (TB) culture. Histology revealed inflamed and ulcerated small bowel mucosa with plump endothelial cells with the appearance below. There were no granulomata (figures 1 and 2). Figure 1Endoscopic examination of the jejunum. Figure 2Plump endothelial cells seen on microscopy.What is the differential diagnosis?