SP04 | SEVERE ACUTE NECROTIZING COLITIS DUE TO <i>ENTAMOEBA HISTOLYTICA</i> IN A PATIENT WITH NEWLY DIAGNOSED ACUTE PROMYELOCYTIC LEUKEMIA: THE IMPORTANCE OF A PROMPT DIAGNOSIS

Parasitic infections are uncommon but might be extremely severe in hematologic malignancies due to immunosuppression and chemoterapy induced mucosal damage. We present here the case of an acute promyelocytic leukemia (APL) patient who developed necrotizing pancolitis secondary to Entamoeba histolytica, highlighting diagnostic and treatment challenges. A 59-year-old male with high-risk APL presented in September 2024. His medical history included Crohn’s disease, thyroid cancer, and obesity. Initial therapy with ATRA and idarubicin led to differentiation syndrome, with ATRA discontinuation. By day 12, peritonitis signs emerged, with mesenteric panniculitis at CT scan. Under broad-spectrum antibiotics (piperacillin/tazobactam, amikacin, daptomycin), symptoms worsened, with ESBL K. pneumoniae isolation. Acute appendicitis required surgery. Histology suggested fungal infection, prompting lyposomal amphotericin B therapy. On day 29, a perianal abscess formed. On D32, a colonoscopy revealed severe ulcerative colitis. Surgical debridement of the abscess and ileostomy were performed. Molecular analysis confirmed E. histolytica infection, requiring metronidazole, paromomycin, and ceftolozane/tazobactam therapy. Hepatic biopsy confirmed liver involvement. After transitory improvement, perianal gangrene led to hemorrhagic shock and total urgent colectomy with rectal amputation was required (day 39). The patient progressively improved, with bone marrow evaluation confirming APL complete molecular remission. Non-disease-related mortality in hematologic malignancies is often associated with infections. Nevertheless severe life-treatening parasitic ethiologies are extremely rare. E. histolytica, an anaerobic protozoan endemic in tropical regions, might cause in immunocompromised hosts necrotizing colitis and systemic manifestations, even if in extremely rare cases. In our patient, the unusually aggressive course of the infection might be correlated to hematologic neoplasia, chemotherapy and preceding long standing inflammatory bowel disease. Notwithstanding appropriate aggressive medical treatment, the infestation resulted in extremely severe pancolitis, requiring demolitive surgical approach. This case highlights the importance of considering also parasitic infestations in immunocompromised hematological patients with gastrointestinal symptoms. Rapid molecular and bioptic procedures have to be timely considered, in order to prevent life-threatening complications.