Pediatric Extreme Thrombocytosis, Etiology, Management and Outcome
Authors: Barg Assaf , Lashansky Adina , Toren Amos , Kenet Gili , Golan Hana 
Published: December 2024

Background :
Extreme thrombocytosis, characterized by a platelet count exceeding 1000 K/µl, is an uncommon occurrence in the pediatric population. Data regarding outcome and management are limited.
Objectives :
To delineate the various etiologies underpinning extreme thrombocytosis in pediatric patients. Secondary objectives encompassed an examination of the duration and severity of extreme thrombocytosis and its potential associations with other hematological parameters, thereby elucidating its etiological nexus. In addition theraputic management and associated thrombotic complications were examined.
Methods :
A retrospective review of electronic medical records spanning a five-year period from a single tertiary medical center was conducted. Patients with platelet counts exceeding 1000 K/µl were selected for further analysis, focusing on a three-month observation period subsequent to the initial documentation of extreme thrombocytosis. The study was conducted according to the guidelines of the Declaration of Helsinki and was approved by the Institutional Review Board.
Results :
Among 204 pediatric patients identified with extreme thrombocytosis, 200 were attributed to secondary causes. The median age at presentation was 1.3 years, with a statistically significant correlation observed between platelet count and age (p=0.02). Infection emerged as the predominant etiological factor, accounting for 43.6% of cases. Notably, asplenia exhibited a statistically significant correlation with platelet count (p&lt;0.001). Almost all patients still had thrombocytosis in the week following the initial event (96%), 46% of which with EXT. Remarkably, among patients with follow-up blood counts one to two months after the initial EXT event, 11% displayed thrombocytopenia, while only 7% still exhibited EXT. In the vast majority of patients prophylactic anti thrombotic therapy was not administered. Regarding primary prophylaxis, for this analysis 19 patients were excluded as they received anticoagulant therapy prior to the diagnosis of EXT. Of the remaining 185 patients 14% (26 patients) were treated with aspirin and their platelet count was higher than patients who did not receive anti platelet therapy (p=0.027). Nine patients had thrombotic events within three months of EXT. There was a trend of higher platelet number amongst patients who experienced thrombosis in comparison to patients without thrombotic complications, however, this did not reach statistical significance (p=0.55).
Venous thrombosis was observed in 8/9 cases of which seven were deep vein thrombosis (DVT) and one was superficial. One patient experienced acute ischemic arterial stroke. In majority of cases DVT was line associated. In 77.8% of cases, thrombosis was diagnosed within 14 days from EXT.
Discussion and Conclusions:
Our findings contribute to a better understanding of extreme thrombocytosis in pediatric patients. EXT was noted among 0.3% of blood counts obtained from children in our tertiary center. Similarly, to non-extreme thrombocytosis, some of the most common causes for EXT were infection and inflammation. Despite the fact that primary EXT is rare in the pediatric population our study's results demonstrate for the first time that secondary EXT may persist for one to two months following the diagnosis.
While thrombotic complications are infrequent, they do occur, predominantly among patients harboring additional risk factors such as central venous lines. Whether EXT serves as an independent risk factor for such events warrants further exploration and the role of primary prophylaxis deserves attention.