Caplacizumab as an add-on therapy in a 7-year-old girl with exacerbated immune-mediated thrombotic thrombocytopenic purpura, a case report and literature review

Abstract

The cornerstone treatment for immune-mediated thrombotic thrombocytopenic purpura (iTTP) in children is a combination of therapeutic plasma exchange (TPE), corticosteroids, and rituximab. Caplacizumab is an anti-von Willebrand factor (VWF) NANOBODY molecule approved as a frontline therapy of iTTP for adults and children aged ≥12 years. Using caplacizumab in children aged <12 years remains a gray area based on recommendations but with no marketing authorization. We report the first case of a pediatric patient with iTTP successfully treated with a caplacizumab dose adjustment of 5 mg daily based on ADAMTS13 activity. We also review all published cases of iTTP in children aged <12 years treated with caplacizumab. This is a 7-year-old girl with clinical thrombotic microangiopathy, in the absence of diarrhea and kidney injury. With a French score of 2 and a PLASMIC score of 7 (high risk), the diagnosis of TTP was suspected and later confirmed by severely low ADAMTS13 activity (<5%). Immune-mediated TTP was distinguished from the congenital one due to the presence of a functional ADAMTS13 inhibitor. Daily TPE and intravenous corticosteroids were started on day 0 (D0). Rituximab was added on D4, and due to refractoriness under daily TPE, we considered off-label administration of caplacizumab from D12. A clinical answer, with a significant increase in the platelet count, was observed within 48 h. A complete ADAMTS13 recovery was reached on D62. No major adverse events were observed during the treatment. She was discharged from the hospital over 3 months ago with a platelet count still within normal ranges. In the literature, we identified a total of four case reports describing five iTTP patients aged <12 years treated with caplacizumab, with a 100% success and tolerability rate. These published data attest to the efficacy and safety of the systematic use of caplacizumab and rituximab as frontline therapy in pediatric iTTP under 12 years of age. Therefore, prospective data are needed to support commercial authorization of caplacizumab in this subpopulation. Close monitoring of ADAMTS13 activity is particularly of interest among children to limit the number of caplacizumab injections.

Keywords: benign hematological disorders; caplacizumab; iTTP; immune-mediated thrombotic thrombocytopenic purpura; pediatrics.

Figure 1

Summary of laboratory parameters and treatment administered in our case. TPE daily, days 0–4 and 6–15, temporarily increased bid days 9–12; intravenous methylprednisolone 1.5 mg/kg daily, days 0–16 temporarily increased to pulse 15 mg/kg/day, days 9–12; oral prednisone 1 mg/kg then slowly tapered, days 13–51; intravenous rituximab, 375 mg/m², on days 7, 10, 15, and 20; caplacizumab 5 mg daily, intravenous day 12 and subcutaneous days 13–54, and then every second day, days 55–64. The functional ADAMTS13 inhibitor level is semiquantitative when the value is >2 BU/ml, ≫2 BU/ml, being the highest. TPE, therapeutic plasma exchange; IV, intravenous; G/L, giga/liter; BU/ml, Bethesda unit/milliliter. ADAMTS13 activity normal range, 51%–100%. Functional ADAMTS13 inhibitor normal range, <0.4 BU/ml.