PB1364 - Study to explore the mechanisms of platelet function abnormalities in patients with Acquired Platelet Dysfunction with Eosinophilia (APDE) utilising Flow Cytometry-based Platelet Function Tests

Background: Acquired Platelet Dysfunction with Eosinophilia (APDE) is a transient bleeding diathesis characterized by muco-cutaneous bleeding due to platelet dysfunction associated with eosinophilia. The postulated pathophysiology of APDE is: parasitic infestation may cause eosinophilia, elevated Immunoglobulin E, release of Platelet activating factor causing platelet activation, degranulation and platelet dysfunction due to acquired mixed-granule deficiency. There are limited studies exploring these mechanisms of platelet dysfunction in APDE.

Aims: To explore the mechanism of platelet dysfunction in APDE utilising flow cytometry-based platelet function tests (FC-PFT)

Methods: Patients diagnosed with APDE(n=12) from January 2021-December 2022 and healthy controls(n=42) were included after informed consent.

Diagnosis was made after comprehensive tests including bleeding history, complete blood counts, peripheral smear(PS) examination, light transmission aggregometry, lumi-aggregometry, Prothrombin time, Activated partial thromboplastin time, Fibrinogen, Factor Assays and Ristocetin Cofactor assay.

Mechanism of platelet dysfunction was explored by FC-PFT to assess ɑ-granule release using CD62P and δ-granule release using CD63 upon agonist stimulation by ADP(30µM), Convulxin(1µg/mL) and TRAP(100µM). Mepacrine uptake/release assay was performed to further classify δ-granule disorder into storage pool defect and secretion defect/signal transduction defect.

Mann Whitney test was used to compare statistical difference between patients and controls.

Results: The median(IQR) duration of bleeding symptoms was 2months(1-12months), which resolved on follow-up examination after adequate treatment of eosinophilia, confirming the diagnosis of APDE. Median(IQR) absolute eosinophil count was 833(600-1143.5) /µL. PS examination showed pathognomic platelet anisogranularity.

CD63 and CD62P expression upon agonist stimulation was reduced in APDE compared to controls, consistent with δ-granule deficiency and ɑ-granule deficiency respectively. Mepacrine uptake and release ratios were reduced in APDE compared to controls, further confirming δ-granule deficiency.

Conclusion(s): FC-PFTs helped explore the pathways involved in causing platelet dysfunction in APDE. The acquired mixed-granule deficiency in APDE was clearly demonstrated by reduced expression of platelet activation markers CD62P, CD63 and reduced Mepacrine uptake/release compared to controls.