LQCL2609 - CMLE - Caplacizumab: The Cause Behind Delayed ADAMTS13 Activity Normalization in Thrombotic Thrombocytopenic Purpura (TTP)-LQCL2609

LQCL2609 - Educational Activity

Pdf Summary

This hematology module reviews thrombotic thrombocytopenic purpura (TTP), a rare, life‑threatening thrombotic microangiopathy caused by severe ADAMTS13 deficiency, leading to accumulation of ultralarge von Willebrand factor (vWF) multimers, platelet-rich microthrombi, thrombocytopenia, microangiopathic hemolytic anemia (schistocytes, elevated LDH/bilirubin), and end‑organ ischemia (often neurologic and renal). Because untreated mortality is very high, treatment should begin promptly when clinical suspicion is high, even if the full classic “pentad” is not present.<br /><br />A case is presented of a 58‑year‑old woman with neurologic symptoms, severe thrombocytopenia, anemia, elevated LDH, and schistocytes, with normal coagulation and renal testing. ADAMTS13 activity was ~5%, confirming TTP. She was treated with plasma exchange (PEX) plus high‑dose corticosteroids, caplacizumab, and rituximab, resulting in rapid clinical improvement and platelet/hematocrit recovery. However, ADAMTS13 activity remained severely low weeks into therapy, prompting concern for an inhibitor. A preanalytical EMR ordering error initially led to ordering ADAMTS13 activity instead of an inhibitor titer; correct inhibitor testing later confirmed an ADAMTS13 inhibitor.<br /><br />The document emphasizes caplacizumab’s mechanism (anti‑vWF A1 domain blocking platelet adhesion) and explains that while it hastens platelet normalization and can reduce needed PEX, it does not suppress the autoimmune process in acquired TTP. Reduced PEX and persistent inhibitors may contribute to delayed ADAMTS13 recovery and relapse after stopping caplacizumab, as seen in clinical trials. Therefore, monitoring ADAMTS13 activity (e.g., using ~30% as a risk cutoff) may be more informative than platelet count alone. Effective lab–clinical communication and correct test ordering are highlighted as essential for optimal monitoring and outcomes.

Keywords

thrombotic thrombocytopenic purpura

TTP

ADAMTS13 deficiency

ADAMTS13 inhibitor

thrombotic microangiopathy

ultralarge von Willebrand factor multimers

microangiopathic hemolytic anemia

plasma exchange

caplacizumab

rituximab