Paper Details

ABSTRACT

Introduction: Acquired Thrombotic Thrombocytopenic Purpura (aTTP) is a rare, life-
threatening condition in the pediatric and adolescent population, characterized by
microangiopathic hemolytic anemia, thrombocytopenia, and microvascular occlusion
leading to multiorgan dysfunction. Therapeutic plasma exchange (TPE) to remove ultra
large von Willebrand factor (VWF) multimers has been the longstanding standard of
care. Caplacizumab, a bivalent monoclonal antibody that inhibits VWF -platelet GP1b
interaction, was approved by the FDA in 2019 for adults and extended age to patients
12 years and older in 2025 based on limited retrospective data. This study aimed to
conduct a real-world analysis comparing outcomes in pediatric patients with
aTTP treated with and without caplacizumab.

Methods: This retrospective cohort study used data from the Pediatric Health
Information System (PHIS), an administrative database encompassing over 50 US
children's hospitals. We identified initial inpatient encounters from 01/01/2016-
12/31/2025 for patients aged 1-21 years with an ICD-10 code for aTTP and a procedure
charge for TPE.  Only the first qualifying encounter for each patient was included.
Descriptive statistics were used to compare patient characteristics and outcomes
between those who received caplacizumab to those who did not. Subgroup analysis
compared patients' caplacizumab receipt among patients aged ≥12 years versus <12
years.

Results: One hundred patients met inclusion criteria, of whom 24 (24%) received
caplacizumab (age range 1-18 years). Sixty-six patients were aged ≥12, and 34 patients
were <12 years. There were no significant differences in age, sex, race/ethnicity, or
insurance payer between groups. Patients who received caplacizumab had longer
median time to 30-day hospital readmission (22.5 vs 7.5 days, p=0.046), although the
overall 30-day readmission rate for aTTP did not differ significantly between groups. No
deaths occurred in the caplacizumab group compared to 8 deaths in the group who did
not receive caplacizumab (p=0.097). Caplacizumab was not associated with
thromboembolic events or hemorrhagic events. There was no significant difference in
the median duration of TPE between groups. The mean ICU length of stay was
lower in the caplacizumab group; however, the difference was not statistically significant.
Median medication-adjusted hospital charges were significantly greater in the caplacizumab
group ($358,858 vs $79,290, p < 0.001).

Discussion: In this real-world, multi-institutional pediatric cohort, caplacizumab use in
aTTP was associated with a prolonged time to 30-day readmission. Mortality rates were
lower in the caplacizumab group, and caplacizumab did not appear to be associated
with thromboembolic or hemorrhagic events. However, its use was associated with
substantially higher pharmacy charges for hospitalizations, underscoring the need for
cost-effectiveness analyses in the pediatric setting. Although results should be
interpreted with caution due to small sample size, this study represents one of the
largest real-world pediatric aTTP cohorts reported to date. It adds to the limited
evidence supporting the potential safety and clinical benefit of caplacizumab in children.