Unmasking Cytomegalovirus Colitis: A Case of Haemorrhagic Colitis in a Patient with Chronic Myeloid Leukaemia on Dasatinib.

Tyrosine kinase inhibitors (TKIs) are the first-line treatment for chronic myeloid leukaemia (CML) with BCR-ABL1 translocation. Dasatinib, a second-generation TKI, is associated with a wide range of adverse effects such as myelosuppression, pleural effusion, diarrhoea, and haemorrhagic colitis in up to 40% of patients. Additionally, its off-target immunomodulatory effects on natural killer cells and T lymphocytes may lead to the reactivation of latent infections, including cytomegalovirus (CMV), a known cause of colitis. We present a case of CMV-associated haemorrhagic colitis in a 69-year-old woman with CML in complete remission, who was being treated with dasatinib. She was admitted to our hospital with a 1-month history of generalized weakness, light-headedness, and intermittent haematochezia. On presentation, she was hypotensive and tachycardic due to haemorrhagic shock. Urgent colonoscopy revealed multiple small ulcers and erosions in the rectum, sigmoid, and transverse colon with signs of active bleeding, which were managed with haemostatic clips. Rectal biopsy initially showed mild, non-specific chronic inflammation. Dasatinib was discontinued due to suspected drug-related colitis. However, post-discharge immunohistochemistry revealed localized CMV inclusions, prompting readmission and initiation of valganciclovir therapy. This case highlights the importance of considering opportunistic infections such as CMV in CML patients receiving TKIs. Given the overlapping clinical and endoscopic features of CMV and dasatinib-induced colitis, histopathological evaluation is essential for accurate diagnosis and timely management. In immunosuppressed patients being treated with dasatinib, haemorrhagic colitis can mask an underlying infection.Tissue biopsy constitutes a key tool for promptly diagnosing cytomegalovirus colitis, enabling clinicians to start treatment early and thus prevent adverse outcomes.