Platelet-Associated IgG May Be Associated with Thrombocytopenia In Patients with Myelodysplastic Syndromes
Authors: Gilli Simone , de Souza Medina Samuel , Castro Vagner , Olalla-Saad Sara T. 
Published: October 2019

Abstract
Abstract 2943

Background.
Myelodysplastic Syndromes (MDS) are a heterogeneous group of bone marrow disorders characterized by ineffective and dysplastic hematopoiesis, progressive bone marrow failure, cytopenias and a high risk of transformation into acute leukemia. Thrombocytopenia is detected in up to two thirds of patients with MDS and severe thrombocytopenia is present in approximately 10%. Besides ineffective thrombopoiesis, immune destruction of platelets could be an additional factor in the genesis of thrombocytopenia, since immunological abnormalities are also frequent in patients with MDS. The detection of platelet associated IgG (PAIgG) by immunofluorescence (platelet immunofluorescence test or PIFT) is a highly sensitive assay. In addition, some morphological platelet indices (PDW and MPV) are correlated with the occurrence of immune thrombocytopenia. We prospectively analysed platelet-bound IgG and platelet indices (PDW and MPV) in 35 patients with MDS.

Methods:
Thirty-five patients with MDS (mean age ± SD: 63 ± 19 yo; range 21–89 yo; 15female/20male) were evaluated. According to FAB, 27 patients were classified as RA, 5 as RARS and 3 as RAEB. Clinical manifestations of immunological disorder were not present in this population. Blood samples were analyzed by PIFT, in order to detect platelet associated IgG and results were expressed as a ratio of patient fluorescence/negative control fluorescence (R). Cell-dyn Sapphire blood cell analyzer (Abbott, Illinois, USA) was used to measure platelet count, mean platelet volume (MPV) and platelet size deviation width (PDW). Thrombocytopenia was defined as a platelet count <100 × 109/L. All samples were analyzed on the day of collection.

Results.
Platelet counts of the entire population ranged from 6.7 to 708 ×109/L, with median of 95.4 × 109/L. Eighteen patients (51.43%) had platelet count <100 × 109/L. A strong association between thrombocytopenia and PAIgG measured by PIFT (R) was demonstrated taking into account three analysis: an inverse correlation between the number of platelets and the fluorescence ratio (p=0.01, r=-0.39, Spearman test), the higher positivity of PIFT in patients with platelet count <100 × 109/L (p=0.007, Wilcoxon rank sum test) and a lower platelet count in patients with positive PIFT (p=0.059, Wilcoxon rank sum test). MPV was significantly higher in patients with platelet count <100 × 109/L (median, min-max: 9.38, 6.9–23.1 vs 8.46, 4.88–12.83; p<0.001, Wilcoxon rank sum test). PDW showed no statistical difference between these groups. Discussion: Immune thrombocytopenia is a relatively frequent hematological disorder of unknown origin and until today depends mainly upon clinical diagnosis. Assays for the detection of glycoprotein-specific antibodies such as MAIPA (monoclonal antibody-specific immobilization of platelet antigens) are highly specific but less sensitive than PIFT. MAIPA is laborious and require a certain amount of platelets, which is not always available in thrombocytopenia Thus, PIFT could be recommended as a screening test to discriminate patients with MDS in whom the hyperdestructive component of thrombocytopenia is important. Our results also showed a higher MPV in patients with platelet count <100 × 109/L, suggesting that this index may be of interest for detection of immune-mediated hyperdestructive thrombocytopenia in MDS.

Conclusion:
Thus, we propose that a combination of a simple index as MPV and a highly sensitive and easy to perform screening test for PAIgG as PIFT could be applied to select a subset of MDS patients in which we would be able to prevent the overuse of unnecessary platelet transfusions and who could be candidates for an immunosuppressive therapeutic approach. Supported by INCTS, FAPESP, CNPq.

Disclosures:
No relevant conflicts of interest to declare.