PA01 ‘Too young to clot?’ Extensive lower-limb thrombosis, phlegmasia alba and distal-limb ischaemia in a young person receiving ritlecitinib for alopecia areata

Abstract Ritlecitinib, a selective Janus kinase (JAK)3/TEC kinase inhibitor, is the first targeted therapy licensed for moderate-to-severe alopecia areata, including in adolescents. While JAK inhibitors have been associated with venous thromboembolism in adult inflammatory disease cohorts, paediatric safety data remain limited. As use expands within paediatric dermatology, understanding rare but serious adverse events is essential. We describe an adolescent with severe alopecia areata who developed extensive ilio­femoral venous thrombosis 13 months after starting ritlecitinib. She presented with an acute, unilateral, painful, swollen leg and impaired mobility. She is an avid rower, of normal weight, and had no personal or family history of thrombosis and no other identifiable risk factors such as the oral contraceptive pill. On assessment, she clinically had phlegmasia alba. Imaging confirmed extensive iliofemoral venous thrombosis. Ritlecitinib was discontinued. She required urgent vascular surgical intervention alongside intravenous heparin and subsequently oral rivaroxaban. She has thankfully recovered with no complications and remains on rivaroxaban. This case highlights a rare but serious complication of ritlecitinib in an adolescent with no conventional thrombotic risk factors. Although absolute risk remains low (trial data reports incidence of 0.06 thrombosis per 100 patient-years), this raises important questions around risk stratification, informed consent and safety monitoring in young people receiving systemic therapy for a non-life-threatening condition. Paediatric dermatologists must appropriately counsel and work with families to make a joint decision regarding ritlecitinib in alopecia areata, balancing the profound psychosocial burden of alopecia areata against potentially life-threatening systemic risks of the medicines. This report adds to emerging postmarketing safety data on ritlecitinib in paediatric populations. Ongoing pharmacovigilance, registry reporting and long-term follow-up are needed to better characterize thrombotic risk and inform safer prescribing for children and young people.