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Abstract
In acquired thrombotic thrombocytopenic purpura (TTP), an immune-mediated deficiency
of the von Willebrand factor-cleaving protease ADAMTS13 allows unrestrained adhesion
of von Willebrand factor multimers to platelets and microthrombosis, which result
in thrombocytopenia, hemolytic anemia, and tissue ischemia. Caplacizumab, an anti-von
Willebrand factor humanized, bivalent variable-domain-only immunoglobulin fragment,
inhibits interaction between von Willebrand factor multimers and platelets.
Severe ADAMTS13 deficiency occurs in 13% to 75% of thrombotic microangiopathies (TMA). In this context, the early identification of a severe, antibody-mediated, ADAMTS13 deficiency may allow to start targeted therapies such as B-lymphocytes-depleting monoclonal antibodies. To date, assays exploring ADAMTS13 activity require skill and are limited to only some specialized reference laboratories, given the very low incidence of the disease. To identify clinical features which may allow to predict rapidly an acquired ADAMTS13 deficiency, we performed a cross-sectional analysis of our national registry from 2000 to 2007. The clinical presentation of 160 patients with TMA and acquired ADAMTS13 deficiency was compared with that of 54 patients with detectable ADAMTS13 activity. ADAMTS13 deficiency was associated with more relapses during treatment and with a good renal prognosis. Patients with acquired ADAMTS13 deficiency had platelet count <30×109/L (adjusted odds ratio [OR] 9.1, 95% confidence interval [CI] 3.4–24.2, P<.001), serum creatinine level ≤200 µmol/L (OR 23.4, 95% CI 8.8–62.5, P<.001), and detectable antinuclear antibodies (OR 2.8, 95% CI 1.0–8.0, P<.05). When at least 1 criteria was met, patients with a severe acquired ADAMTS13 deficiency were identified with positive predictive value of 85%, negative predictive value of 93.3%, sensitivity of 98.8%, and specificity of 48.1%. Our criteria should be useful to identify rapidly newly diagnosed patients with an acquired ADAMTS13 deficiency to better tailor treatment for different pathophysiological groups.
Discoveries during the past decade have revolutionized our understanding of idiopathic thrombotic thrombocytopenic purpura (TTP). Most cases in adults are caused by acquired autoantibodies that inhibit ADAMTS13, a metalloprotease that cleaves von Willebrand factor within nascent platelet-rich thrombi to prevent hemolysis, thrombocytopenia, and tissue infarction. Although approximately 80% of patients respond to plasma exchange, which removes autoantibody and replenishes ADAMTS13, one third to one half of survivors develop refractory or relapsing disease. Intensive immunosuppressive therapy with rituximab appears to be effective as salvage therapy, and ongoing clinical trials should determine whether adjuvant rituximab with plasma exchange also is beneficial at first diagnosis. A major unanswered question is whether plasma exchange is effective for the subset of patients with idiopathic TTP who do not have severe ADAMTS13 deficiency.
[1
]From the Department of Haematology, University College London Hospitals, Cardiometabolic
Program, National Institute for Health Research UCLH–UCL Biomedical Research Center,
London (M.S.); the Division of Hematology, Department of Internal Medicine, Ohio State
University, Columbus (S.R.C.); Fondazione Istituti di Ricovero e Cura a Carattere
Scientifico Ca’ Granda Ospedale Maggiore Policlinico, Angelo Bianchi Bonomi Hemophilia
and Thrombosis Center, and the Department of Pathophysiology and...
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