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Thrombocytopenia in a cohort of primary and secondary antiphospholipid syndrome patients: Relation to clinical, laboratory manifestations and damage index

Objectives This study aims to evaluate the prevalence of thrombocytopenia in a cohort of patients with primary and secondary antiphospholipid syndrome (APS) and to examine the relation of thrombocytopenia to the clinical, laboratory findings, and damage index for antiphospholipid syndrome (DIAPS). Patients and methods Between August 2018 and February 2019, a total of 168 patients (16 males, 152 females; mean age: 32.5±8.4 years; range, 18 to 59 years) who were followed in our clinic for APS were retrospectively analyzed. Medical records of the patients were screened and clinical data, laboratory investigations, and treatments applied were recorded. The DIAPS was calculated for all patients. The patients were divided into two groups according to the presence or absence of thrombocytopenia and both groups were compared regarding clinical, laboratory findings and DIAPS. Further subgroup analysis was done for patients with primary APS. Results The most common clinical manifestations in our patients were obstetric manifestations (77.4% in pregnant women), musculoskeletal manifestations (69%) and peripheral vascular thrombosis (54.8%). The prevalence of thrombocytopenia in our study was 42.3%, and it was significantly associated with musculoskeletal manifestations (p=0.043), vascular thrombosis (p=0.043), neurological manifestations (p=0.030), cutaneous manifestations (p=0.006), and use of immunosuppressives (p=0.047). The DIAPS was significantly higher in the thrombocytopenia group (p=0.034). Further subgroup analysis of patients with primary APS revealed that neurological manifestations (p=0.010) were significantly higher in the thrombocytopenia group, while the DIAPS was higher in the thrombocytopenia group, but it did not reach statistical significance (p=0.082). Conclusion Thrombocytopenia may be associated with a higher incidence of vascular thrombosis, neurological manifestations, musculoskeletal manifestations, use of immunosuppressive treatment, and DIAPS. In primary APS patients, thrombocytopenia may be a risk for neurological manifestations.

Antiphospholipid syndrome (APS) is an autoimmune-mediated acquired thrombophilia. 1,2 It is defined as a syndrome of recurrent venous and/or arterial thromboses, pregnancy complication together with the presence of antiphospholipid antibodies (aPL), that are directed against phospholipid-binding plasma proteins. [1][2][3] Thrombocytopenia is one of the most common non-criteria findings in APS patients. 4 The estimated prevalence of thrombocytopenia in patients with APS ranged from 20 to 53%, depending on the cut-off value used (<100¥10 9 /L or <150¥10 9 /L), 5 and the frequency of patients with primary APS (PAPS) and secondary APS (SAPS) in the studied cohort. [6][7][8] Interestingly, the prevalence of thrombocytopenia may reach up to 65 to 100% in patients with catastrophic APS (CAPS). 8,9 Thus, some authors have suggested that a progressive decrease in the platelet count in APS patients may be considered a sign for progressive disease and be a risk factor for developing CAPS in the future. 1,10 Furthermore, Artim-Esen et al. 4 reported coexistence of thrombocytopenia and neuropsychiatric manifestations, in association with lupus anticoagulant and high titers of anticardiolipin antibodies.
Although several studies have been conducted on thrombocytopenia in APS patients to date, 6,[11][12][13] there are important issues that still need to be addressed, such as relation of thrombocytopenia to clinical associations of APS, its effect on the disease outcomes, and finally the relation of thrombocytopenia to the APS damage index (DIAPS). In the present study, we aimed to evaluate the prevalence of thrombocytopenia in patients with APS and to examine the relation of thrombocytopenia to the clinical and laboratory findings, and DIAPS.

PATIENTS AND METHODS
This single-center, retrospective study was conducted at Cairo University Hospital, Faculty of Medicine, Department of Rheumatology, between August 2018 and February 2019. A total of 168 patients (16 males, 152 females; mean age: 32.5±8.4 years; range, 18 to 59 years) who were followed in our clinic and fulfilled the update of Sapporo Classification Criteria for definite APS 14 were included. The medical records were revised for demographic data, clinical features of the disease, immune profile, routine laboratory investigations, and treatments applied. In addition, the DIAPS 15 was calculated for all patients. The patients were divided into two groups according to the presence or absence of thrombocytopenia and both groups were compared regarding demographic data, clinical, laboratory findings, treatments, and DIAPS. Patients less than 18 years old or with disease duration of less than two years were excluded from the study. Thrombocytopenia was considered a clinical feature of APS in our study, when the platelet count of less than 150¥10 9 /L was found on a minimum of two occasions. 11 Further subgroup analysis was done for patients with PAPS according to the presence or absence of thrombocytopenia.

Statistical analysis
Statistical analysis was performed using the SPSS for Windows version 23.0 software (IBM Corp., Armonk, NY, USA). Descriptive data were expressed in mean ± standard deviation (SD) or median (min-max) for quantitative variables and in number and frequency for qualitative variables. Comparison between the groups was conducted using the Student t-test for normally distributed data and Mann-Whitney U test for skewed data. The chi-square test was used analyze qualitative variables. A p value of <0.05 was considered statistically significant.
The laboratory features of our patients in the last visit, their treatment and DIAPS are shown in Table 2. Our patients were divided into two groups according to presence or absence of thrombocytopenia, the two groups were compared regarding demographic, clinical, laboratory, treatments, and DIAPS as shown in Table 3. Furthermore, we studied patients with PAPS to exclude any impact of associated disease, and we divided them into two groups according to the presence or absence of thrombocytopenia and both groups were compared regarding the previously mentioned items as shown in Table 4.

DISCUSSION
The estimated prevalence of thrombocytopenia in APS in the literature ranges between Regarding obstetric manifestations, we could not detect significant associations between thrombocytopenia and obstetric morbidity in our patients. On the other hand, our results showed a high rate of overall neurological manifestations in thrombocytopenia group compared to non-thrombocytopenia group (50.7% vs. 34%) with a statistically significant difference (p=0.03). We also found a strong association between thrombocytopenia and musculoskeletal manifestations (77.5% vs. 62.9%) (p=0.043). Similarly, Krause et al. 6 reported that obstetric complications were similar in patients with and without thrombocytopenia and that the presence of thrombocytopenia might be a risk factor for neurological and articular manifestations. Also, Artim-Esen et al. 4 reported that thrombocytopenia represents a risk factor for thrombosis and neurological manifestations in aPL-positive patients.
Our results showed a high rate of venous thrombosis in thrombocytopenia group compared to non-thrombocytopenia group (50.7% vs. 43.3%); however, this was not statistically significant (p=0.342). A high rate of arterial thrombosis was also found in thrombocytopenia group compared to the other, but also this was not statistically significant (18.3% vs. 11.3%) (p=0.202). Also, total peripheral vascular thrombosis was higher in the positive group compared to the negative group (63.4% vs. 48.5%), with a p value quite close to the significant value (p=0.055). Comparing the two groups regarding total thrombotic events (peripheral vascular and internal organs), thrombocytopenia group showed a higher incidence of total thrombosis (77.5% vs. 62.9%) with a significant p value of 0.043, although the rate of thrombosis in the study conducted by Krause et al. 6 was slightly higher in the thrombocytopenia group; however, it did not reach statistical significance. On the other hand, Atsumi et al. 16 reported that the presence of thrombocytopenia in patients with APS was not typically associated with hemorrhagic complications; rather, it could trigger thrombotic events. It was also found that the more severe the thrombocytopenia, the higher the possibility of future thrombosis. Also, Pontara et al. 8 reported that a decrease in platelet count was associated with the development of the catastrophic form of the disease, a decrease in platelet count in highrisk APS patients should be evaluated cautiously for the disease progression to CAPs.
Furthermore, our results are in accordance with Demetrio Pablo et al., 17 as they reported that aPL-positive patients who developed thrombocytopenia had a potential risk of developing thrombosis. In addition,    Abreu et al. 18 showed that thrombocytopenia in APS was a consequence of consumption of platelets, as binding of aPL antibodies, particularly anti-beta-2 glycoprotein antibodies, to the surface of activated platelets promoted their aggregation and thrombus formation. Finally, Proulle et al. 19 showed that, among aPL-positive patients, thrombosis might develop more frequently in patients with a low platelet count, compared to those without. Although Krause et al. 6 found significant associations between thrombocytopenia and cardiac valves thickening and dysfunction, our results showed no statistically significant difference between the two groups regarding overall cardiac manifestations.
Regarding cutaneous manifestations (cutaneous ulcers, digital gangrene, livedo, thrombophlebitis), our results showed an overall increase in the rate of cutaneous manifestations in the thrombocytopenia group compared to the other group (45.1% vs. 24.6%) with a statistically significant difference (p=0.006). Similarly, Krause et al. 6 and Comellas-Kirkerup et al. 20 reported significant associations between thrombocytopenia and cutaneous manifestations including livedo reticularis and skin ulcerations. Furthermore, many reports have suggested that livedo reticularis may be associated with more severe disease, as it may be associated with thrombosis, 21 and also it may be associated with stroke. 22 In our study, both thrombosis and stroke were significantly higher in the thrombocytopenia group and this is in line with the findings of Artim-Esen et al. 4 Moreover, the association of thrombocytopenia with neurological manifestations was also confirmed in our PAPS cohort.
The significantly higher usage of immunosuppressive in the thrombocytopenia group, in our study, was expected as thrombocytopenia, particularly if severe, may require treatment with high dose glucocorticoids, immunosuppressive drugs, and rituximab along with intravenous immunoglobulin and plasma exchange. [23][24][25] Damage index for APS was significantly higher in thrombocytopenia group (p=0.034). This may be a sequence of the higher prevalence of neurological manifestations, thrombosis and cutaneous manifestations, all of which may be associated with more damage. Also, thrombocytopenia itself may be a sign of more aggressive disease and may require treatment with immunosuppressors adding to the disease burden and may affect the disease outcome. To the best of our knowledge, no previous study has compared damage accrual in APS patients with and without thrombocytopenia; however, Ruiz-Irastorza et al. 26 concluded that APS associated with thrombosis might present more damage in SLE. Furthermore, Artim-Esen et al. 4 reported that thrombocytopenia was a risk factor for thrombosis in aPL-positive patients. All the aforementioned data may give a reasonable explanation of the higher damage index in the thrombocytopenia group.
On analyzing PAPS patients and although DIAPS was higher in PAPS patients with thrombocytopenia (2.1±2.2) compared to (1.1±1.7) in those without, the difference did not reach statistical significance (p=0.082). Similarly, venous thrombosis, arterial thrombosis, and total peripheral vascular thrombosis were higher in thrombocytopenia group; however, the difference did not reach statistical significance (p=0.062). The lack of association of thrombocytopenia with DIAPS and arterial thrombosis, although p value quite close to significant in both situations, may be due to the small sample size of patients with PAPS in the current cohort. In our opinion, thrombocytopenia may represent more than an incidental laboratory finding in APS patients, and further studies may be needed to explore its role in APS pathogenesis and in damage occurrence in APS patients.
The small number of patients with PAPS included in the current study is the main limitation. We, therefore, recommend further studies on thrombocytopenia to be conducted on a large cohort of PAPS patients to avoid the impact of any associated disease as SLE on APS characteristics and DIAPs.
In conclusion, thrombocytopenia may be associated a with higher incidence of vascular thrombosis, neurological manifestations, musculoskeletal manifestations, use of immunosuppressive treatment, and DIAPS. In PAPS patients, thrombocytopenia may be a risk for neurological manifestations; however further large-scale studies are needed to confirm our findings.