Evolution of Anti-ADAMTS13 Antibodies in a Refractory Case of Thrombotic Thrombocytopenic Purpura with Fatal Outcome

Thrombotic thrombocytopenic purpura (TTP) is characterized by systemic microvascular thrombosis leading to life-threatening ischemia of multiple organs, and is associated with a severe deficiency of the von Willebrand factor (VWF)-cleaving protease ADAMTS13, which permits highly adhesive ultra-large VWF multimers to accumulate in the circulation. Inhibitory and less frequent non-inhibitory anti-ADAMTS13 autoantibodies have been detected in patients suffering from acquired idiopathic TTP. Current treatment with plasma exchange therapy is considered to remove the autoantibodies while concomitantly supplying plasma with the deficient protease. Plasma therapy greatly reduces mortality, nevertheless, still about 10% of the patients die from refractory TTP. To explore the cause of treatment failure in a fatal case of idiopathic acquired TTP we investigated retrospectively the anti-ADAMTS13 immunological profile of a 70-year-old female patient during the course of disease progression. At admittance, she presented with schistocytes, thrombocytopenia and severe neurological disturbances. ADAMTS13 antigen and activity were borderline low in the presence of initially non-inhibiting anti-ADAMTS13 IgG and IgM antibodies, no ADAMTS13 gene aberrations were detected. She had had no previous episodes of TTP. During treatment, the patient received repeated plasma exchanges, supportive extracorporal immunoadsorption and corticosteroid therapy. Despite ongoing treatment anti-ADAMTS13 antibodies still developed and ADAMTS13 activity remained less than 0.1U/ml. After 5 weeks of therapy, during which time the patient was seriously ill with striking neurological limitations, her platelet count dropped and a splenectomy was performed. The patient’s state improved despite a complicated postoperative phase. During the next 4 weeks, her platelet count increased gradually up to 780 G/L, a moderately low ADAMTS13 activity of 0.24U/ml (0.57ng/ml ADAMTS13 antigen) was detected and ADAMTS13-specific antibodies were not measurable. However, within a few days her platelet count dramatically dropped to 20G/L, anti-ADAMTS13 antibodies reappeared and ADAMTS13 activity again was undetectable. The patient’s state deteriorated and she died 2 days later from multiple organ failure. We show the results of the fluctuating anti-ADAMTS13 antibody profile (functional inhibitors and total IgG, IgG subtypes, IgA and IgM) and the pattern of the ADAMTS13 domain-specific reactivity superimposed with the common clinical laboratory data over the patient’s 9-week clinical course.