RETROSPECTIVE EVALUATION OF CLINICAL AND ECONOMIC OUTCOMES IN IMMUNE THROMBOTIC THROMBOCYTOPENIC PURPURA PATIENTS TREATED WITH OR WITHOUT CAPLACIZUMAB

Plasma exchange (PE) using fresh frozen plasma (FFP) is the first-line treatment for immune thrombotic thrombocytopenic purpura (iTTP). Caplacizumab (Cap), anti-von Willebrand Factor antibody, demonstrated early improvement in platelet function and reduced the incidence of PE (NEJM 2016;374:511-522). The 2023 TTP Clinical Practice Guidelines state that Cap is the first-line treatment for iTTP. iTTP is a rare disease, and the actual state of treatment in the real world and changes in healthcare costs before and after Cap have not yet been sufficiently reported.

We conducted a retrospective cohort study at our hosipital, including patients diagnosed with iTTP between April 2012 and July 2025. 16 patients were divided into 11 patients treated without Cap (non-Cap group) and 5 patients treated with Cap (Cap group). The primary outcome was defined as a clinical response, indicated by either a sustained platelet count of ≥150,000/μL for at least two consecutive days, or a stable plateau of platelet count within the normal or supranormal range for three consecutive days. Secondary outcomes included ADAMTS13 remission, defined as an activity level ≥50%, and the total cost of PE and Cap. Continuous variables are presented as median (IQR), and categorical variables as percentages. Group differences were evaluated using the Wilcoxon rank sum test. Survival was analyzed by Kaplan–Meier with group comparisons by log-rank test and hazard ratios estimated from Cox models.

Age was 64 (56-76) years in the non-Cap group and 80 (35-88) years in the Cap group, with female proportions of 45% and 60%. Platelet count (0.8 [0.8-1.0] vs. 0.7 [0.5-1.25] ×10⁴ /μL, p=0.53), serum creatinine (0.98 [0.7-1.08] vs. 0.91 [0.75-2.47] mg/dL, p=0.4), and ADAMTS13 activity (0 [0-0.04] vs. 0[0-0] IU/mL, p=0.1) showed no significant differences between groups. ADAMTS13 inhibitor levels were 1.9 [0.8-2.8] vs. 3.0 [1.35-7.55] B.U/mL (p=0.26). All patients were treated with oral glucocorticoid. Intravenous steroid pulse therapy was administered to 7 patients in the non-Cap group and 3 patients in the Cap group. And all patients in the non-Cap group and 4 out of 5 patients in the Cap group received rituximab. One patient in the Cap group received cyclophosphamide. All cases of PE underwent FFP transfusion, with no difference in PE volume (4320 [3270-4800] vs. 3940 [3155-5345] mL, p=0.65). However, the number of PE sessions (13 [11-17] vs. 5 [3-9.5], p<0.05) and duration of PE (18 [13-22] vs. 5[3-12.5] days, p<0.05) were significantly lower in the Cap group. In the non-Cap group, 2 patients died on days 10 and 14 after treatment initiation, respectively, while in the Cap group, 1 patient died on day 0 due to disease progression. The Cap group achieved a significantly faster clinical response compared to the non-Cap group (18 [6-70] vs. 5 [4.5-6.5] days; log-rank p<0.05).　Excluding death cases, remission of ADAMTS13 was achieved in both groups, with no significant difference observed at that time (33 [20-51] vs. 45 [28-116.5] days; log-rank p=0.26). The total cost of PE and Cap tended to be higher in the Cap group (3816 [3278-5577] vs. 20051 [9425-34731] ×10³ yen, p=0.07).

The Cap group showed a significantly shorter time to platelet recovery, not time to ADAMTS13 remission. Despite reductions in the number of PE sessions, the cost of PE and Cap was higher in the Cap group, primarily due to the high cost of Cap.