Decoding acquired platelet dysfunction with eosinophilia: Clinical triad and flow cytometric signatures

Abstract

Abstract Background Acquired Platelet Dysfunction with Eosinophilia (APDE) is a rare, under-recognized bleeding disorder seen mainly in tropical regions, presenting with mucocutaneous bleeding, eosinophilia, and abnormal platelet function. Its pathogenesis is unclear, with proposed mechanisms including eosinophil granule–mediated membrane injury, immune effects, or cytokine-driven megakaryocytic dysfunction. APDE mimics inherited platelet function disorders (PFDs) leading to delays, misdiagnosis, and unnecessary genetic testing—especially in children and adolescents with short symptom duration, thrombocytopenia, or macrothrombocytopenia. While Light Transmission Aggregometry (LTA) is the diagnostic gold standard, it is limited in thrombocytopenia; flow cytometry provides a valuable alternative by directly assessing activation markers, dense granule content, and function even at low platelet counts.Aim & ObjectivesPrimary Objective: Identify clinical and peripheral blood clues that can facilitate early differentiation of APDE from inherited platelet function disorders.Secondary Objective: Evaluate the diagnostic utility of flow cytometry–based platelet function testing in APDE, particularly in thrombocytopenic cases where LTA is not feasible.Exploratory Objective: Assess whether unsupervised clustering of flow cytometric parameters can identify phenotypic subgroups within APDE with differing bleeding severity. Methods Study Design & Setting: Retrospective observational cohort study at the Department of Immunohematology and Blood Transfusion, CMC Vellore, from July 2020 to June 2025. Population: Consecutive patients with suspected platelet function disorders who were diagnosed with APDE based on clinical phenotype, eosinophilia (AEC >500/µL), abnormal platelet function testing, and exclusion of inherited PFDs. Data Collection: Demographics, ISTH-BAT scores, CBC, AEC, platelet morphology, bleeding time, PFA-200, LTA, and flow cytometry parameters (CD41, CD42b, CD62P, CD63, mepacrine uptake/release). Flow Cytometry: Beckman Coulter flow cytometer; abnormal thresholds based on institutional reference ranges. Statistical Analysis: Descriptive statistics, comparative analysis with inherited PFDs, Spearman correlation, and unsupervised hierarchical clustering. p < 0.05 was considered significant.Results Demographics: n = 34 APDE patients; median age 12 years; 74% <18 years; 60% female; median ISTH-BAT score 4; median duration 3 months; 82% with symptoms <6 months. Peripheral Findings: Eosinophilia (100%, median AEC = 1800/µL), thrombocytopenia in 10%, platelet anisogranularity in 100%. The triad of short history, eosinophilia, and anisogranularity was present in 91% (p < 0.01 vs. inherited PFDs). Platelet Function Testing: Prolonged bleeding time in 68%, prolonged PFA-200 in 62%, abnormal LTA in 91% of tested patients, not feasible in 3 due to thrombocytopenia. Flow Cytometry: Reduced CD62P in 88%, reduced CD63 in 79%, abnormal mepacrine uptake/release in 88%. δ-SPD-like phenotype in 76% Correlation: Weak negative correlation between mepacrine uptake/release and ISTH-BAT score; CD62P/CD63 not significantly correlated with bleeding severity. Phenotypic Clustering: Severe phenotype with higher BAT scores and more frequent prolonged PFA-200; milder phenotype with partially preserved activation markers. Overlap Disorders: 2 cases with combined BSS + APDE phenotype.Discussion Early clinical clues—short history, eosinophilia, platelet anisogranularity—are valuable in differentiating APDE from inherited PFDs. Flow cytometry is particularly useful in thrombocytopenic patients where LTA is not feasible, identifying dense granule defects in the majority. Phenotypic subgrouping by flow cytometry can stratify bleeding risk. Overlap with other disorders necessitates a broad diagnostic approach.Conclusion APDE is a diagnostic blind spot often mistaken for inherited platelet disorders. A simple triad—short bleeding history, eosinophilia, and platelet anisogranularity—offers a rapid early signal. Flow cytometry bridges gaps when LTA is unfeasible, enabling phenotyping that improves recognition, reduces misdiagnosis, and guides targeted management.