Antiboby mediated Acquired Glanzmann Thrombasthenia – a diagnostic and therapeutic challenge – with Concizumab as Promising Therapeutic Approach: A Case Report

Introduction Acquired Glanzmann thrombasthenia (aGT) is a rare autoimmune bleeding disorder caused by inhibitory antibodies against GPIIb/IIIa, leading to impaired platelet aggregation and severe bleeding. This closely mimics classic GT where isoantibodies render donor platelets ineffective. Thus, rFVIIa and antifibrinolytics are the treatment of choice [ 1 ]. Immunosuppressive approaches such as corticosteroids, intravenous immunoglobulins, and rituximab show variable efficacy, particularly in the presence of IgM antibodies [ 2 ] [ 3 ]. A 12‑year‑old boy, ten years after heart transplantation due to CMV‑induced myocarditis, presented with recurrent severe gastrointestinal bleeding and extensive petechiae. Routine coagulation parameters were normal, except mild thrombocytopenia (around 100,000/µl). After diagnostic gastrointestinal biopsies, he suffered life-threatening hemorrhage requiring massive transfusion of erythrocytes, platelets, fresh frozen plasma, rFVIIa, fibrinogen, and FXIII to stabilize. Method Light transmission aggregometry (LTA) showed absent aggregation responses except ristocetin (1M) consistent with the pattern of GT. MAIPA revealed platelet antibodies against the GPIIb/IIIa complex. LTA with platelets of a healthy control and patient`’s plasma failed to improve aggregation consistent with the hypothesis of antibody-mediated aGT. Further investigations with antibody depletion and purification raised the suspicion that besides IgG antibodies also IgM anti-platelet antibodies play a significant role in this thrombocytopathy. Next‑generation sequencing revealed a heterozygous LRBA deficiency as a potential cause of immune dysregulation. Results Specific treatment included plasma exchange, high‑dose corticosteroids, intravenous immunoglobulins, rituximab, daratumumab, and abatacept, without improvement in platelet function. The patient experienced several life-threatening bleeding events, with only short term bleeding control upon administration of recombinant FVIIa and antifibrinolytics, followed by severe rebleeding with every dose reduction. Due to the need for prophylactic measures to prevent refractory bleedings, Concizumab, a monoclonal antibody inhibiting tissue factor pathway inhibitor (TFPI), was initiated as off‑label therapy after approval for cost coverage. Following subcutaneous administration, bleeding episodes ceased for the first time since disease onset. No further major hemorrhages occurred, petechiae regressed, and transfusion requirements stopped. Conclusion Acquired GT can cause sudden life-threatening bleedings even in children. This case demonstrates that aGT with persistent IgM anti‑GPIIb/IIIa antibodies can be resistant to standard treatments and immunosuppression. Concizumab led to sustained clinical improvement and effective bleeding control , representing a promising therapeutic approach for refractory aGT. TFPI inhibition may offer a novel concept for managing severe autoimmune and congenital platelet function disorders. Publication History Article published online: 17 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany