PO83 | A case of deep vein thrombosis in a patient with systemic mastocytosis

Background: Systemic mastocytosis (SM) is a clonal hematological disorder characterized by the abnormal accumulation of mast cells, leading to uncontrolled degranulation (mast cell activation syndrome, MCAS) in tissues such as the bone marrow, liver, and spleen. Patients with SM may experience exacerbated or abnormal allergic reactions and may be at increased risk of thrombotic events due to coagulation disorders and the production of pro-coagulant factors, along with a reduction in anti- coagulant factors. Case Report: This case report describes a 69-year-old man with SM and left arm deep vein thrombosis (DVT) diagnosed in October 2023. The aim is to outline the therapeutic challenges in managing the underlying pathology. DVTs are common in patients with SM, and if persistent, they require long-term therapy. The patient, a 69-year-old man diagnosed with SM 8 years ago, had reported anaphylactoid crises following drug intake, food ingestion, or insect bites. In October 2023, he was diagnosed with DVT in the left femoropopliteal section, for which he began enoxaparin treatment at 100 U/Kg twice daily. To improve compliance, the patient consulted an allergist and, under strict anaesthesiology surveillance, started oral therapy with apixaban 5 mg twice daily from 17 July 2024. Over the last six months, the patient reported no bleeding or anaphylactic reactions, which contributed to an improvement in his quality of life. Conclusions: This clinical case highlights the importance of an integrated, multidisciplinary approach in managing both the underlying disease and the risk of thrombotic events. The use of anticoagulants may have an unpredictable response due to altered sensitivity to mediators released by mast cells. Direct oral anticoagulants (DOACs) are generally well tolerated, but there are no specific literature recommendations for their use in this patient population. Ongoing research is essential to better understand the mechanisms behind these complications and improve clinical management.