An unusual cause of massive rectal bleeding.

A 76-year old female was referred to the gastro-enterology department because of massive rectal bleeding with hemoglobin decrease to 9 g/dL. She was in follow-up at the oncology department for a multiple myeloma and treated with Lenalidomide-Dexamethason since 2018. She had a past medical history of rectal bleedings due to angiodysplastic lesions of the right colon, treated with argon plasma coagulation (APC). The last left colonoscopy in 2019, performed for chronic diarrhea, was macroscopically normal and histopathologic examination ruled out a microscopic colitis. During colonoscopy significant edema of the caecal-colon ascendens and recto-sigmoidal mucosa was seen, with important submucosal hematomas and some bleeding mucosal tears. The remaining colon mucosa was slightly reddish (Figure 1: A and B). What is your diagnosis?