A Comparative Prospective Observational Study of Children and Adults with Immune Thrombocytopenia: 2-Year Follow-up
Authors: Kuehne Thomas , Schifferli Alexandra 
Published: November 2019

Abstract
Introduction
It is widely accepted that immune thrombocytopenia (ITP) of children differs from that of adults in the clinical course, such as the rate of spontaneous remission, the bleeding risk and the need of treatment. However, this assumption is limited by incongruity of study populations and divergences of collected information, definitions, study objectives and end-points. Surprisingly, data of the Pediatric and Adult Registry on Chronic ITP (PARC-ITP) at initial diagnosis demonstrated far less differences in clinical and laboratory findings between children and adults than expected (Kühne et al. Haematologica 2011). This suggests that newly diagnosed ITP may be driven by similar pathophysiological mechanisms. Differences may occur in the ability of restoring tolerance. We analyzed 6-, 12-, and 24-month follow-up data of children and adults recorded in the PARC-ITP Registry.
Design and Methods
PARC-ITP is an international multi-center registry designed to collect data prospectively of children and adults with newly diagnosed ITP, and was opened in May 2004. Demographic information, diagnostic methods, clinical data, and efficacy and safety of management are continuously registered at the time of diagnosis, 6 and 12months and then yearly. Patients younger than 3 months (n=167) and those with a platelet count of >100x109/l were excluded from the analysis. Patients with missing follow-up data at certain time-points were not excluded. Remission of ITP was defined as a platelet count of >100x109/l at any time point and regardless of therapy. Platelet counts of chronic ITP were defined as being <100x109/l at 12 or 24 months. The data were analyzed with descriptive statistics.
Results
A total of 3'780 evaluable patients with the initial diagnosis of primary ITP were recorded in the PARC-ITP database between 2004 and 2015. There were 3360 children (3 months - 16 years) and 420 adults (≥16 years). The pediatric female: male ratio was 1:1.09, and that of adults was 1:0.54. Follow-up information was available for 67% of children at the 6-month, 49% at the 12-month and 31 % at the 24-month evaluation and in adults in 77%, 64%, and 47%, respectively. In children remission was seen at 6, 12 and 24 months in 70%, 70%, and 71%, and in adults in 45%, 49%, and 56%, respectively. Of the patients with a platelet count of <100x109/l at 6 months, 212/590 children (36%) and 42/152 adults (28%) achieved again a remission at 12-months. The platelet counts of children and adults with chronic ITP at 12 months were 46±30x109/l and 51 ±26x109/l. Adults with a diagnosis of chronic ITP at 12 and 24 months reported having no bleeding in 69% and 65% for the last follow-up period, children in 37% at both time-points. Children with thrombocytopenia at 6, 12 and 24-months received platelet-enhancing drugs in 58%, 46% and 47% and adults in 58%, 52% and 40%, respectively. The diagnosis of secondary ITP and other causes of thrombocytopenia was reported for 123 children, i.e. 3.5%, 1.9% and 1.3% at 6, 12 and 24 months, respectively and 21 adults, i.e. 3.7%, 2.3% and 1.7% at 6, 12 and 24 months, respectively. The reported cause was an infectious disease in both children (49%) and adults (52%).
Discussion
The PARC-ITP Registry is the first cohort of ITP patients including a mixed pediatric and adult population. Limitations include the variety of participating centers (n=74), data registration on a voluntary basis, a high percentage of loss of follow-up and an unbalanced number of children and adults. Preliminary analyses of follow-up data demonstrate similarities between children and adults in much more areas, than previously assumed. Differences in remission rates where confirmed but in a smaller extent than expected. Treatment requirement in patients with active disease was very similar in both age groups. Surprisingly, adults with a diagnosis of chronic disease exhibited a greater number of a non-bleeding phenotype than children.
Conclusion
Understanding differences or similarities among children and adults with ITP may guide in finding immune modulatory strategies with the goal of achieving early sustained responses.

Disclosures
Kuehne: Amgen: Research Funding; UCB Biosciences GmbH: Consultancy. Schifferli:Amgen: Research Funding.