Introduction

Thrombocytopenia is frequent in patients with connective tissue disease (CTD). Immune thrombocytopenia (ITP) may be a primary condition or it can be associated with other disorders, such as CTD. The systemic lupus erythematosus (SLE)-associated thrombocytopenia occurs in approximately 30% of cases1. The primary goal of therapy for patients with chronic thrombocytopenia is to prevent severe bleeding by increasing platelets to 30 × 109/L to 50 × 109/L with few treatment-associated toxic effects2. At present, corticosteroids are used as the first-line therapy for CTD-related thrombocytopenia and second-line treatments, including immunosuppressive drugs, thrombopoietin (TPO), intravenous immunoglobulin (IVIG), splenectomy, and rituximab. Yet, not all patients respond well to this type of therapy.

Eltrombopag is an oral, small molecule, non-peptide thrombopoietin-receptor agonist that interacts with the transmembrane domain of the thrombopoietin receptor2. It promotes the proliferation and differentiation of megakaryocytes in bone marrow, resulting in a dose-dependent increase in normally functioning platelets2. Eltrombopag was approved by the FDA in 2008 for the treatment of ITP. Its efficacy and safety have been confirmed by many clinical and real-world trails in the course of the last ten years. However, so far, no clinical trials have been performed to evaluate the efficacy or safety of eltrombopag in patients with secondary ITP related to CTD. Few case reports have shown promising outcomes in SLE patients3,4,5. It showed that TPO mimetics are safe and good options for SLE-associated thrombocytopenia refractory to conventional immunosuppressive agents, and do not contribute to increased disease activity3,4,5. However, there is limited data on other CTD diseases except for SLE. Overall, more data are needed to confirm whether patients with CTD benefit from eltrombopag, taking into consideration the risk of severe adverse events, such as worsening of the underlying autoimmune dysregulation or thrombosis.

Herein, we presented 15 CTD-related thrombocytopenia cases treated with eltrombopag in Renji Hospital, Shanghai Jiao Tong University, between January 2018 and August 2019.

Materials and methods

A total of 15 hospitalized patients with thrombocytopenia associated to CTD, including 9 patients with SLE, 3 patients with Sjögren’s syndrome (SS), and 3 other patients diagnosed with undifferentiated connective tissue disease (UCTD) in the Renji hospital, Shanghai between January 2018 and August 2019 were enrolled in the study. We confirmed that informed consent was obtained from all subjects or, if subjects are under 18, from a parent guardian. All included patients showed a poor or no response to prior high-dose steroids and immunosuppressant, such as cyclosporine A, azathioprine, and rituximab, as defining refractory thrombocytopenia associated with CTD. Inclusion criteria were: (a) subjects who fulfilled the Systemic Lupus International Collaborating Clinics Criteria (2012) for SLE6, American College Rheumatology (ACR), and European League Against Rheumatism criteria (EULAR) (2016) for SS7 or diagnosed with UCTD; (b) the baseline platelet counts ≤ 30 × 109/L. Patients with arterial thrombosis, a history of venous thrombosis necessitating anticoagulation therapy, splenectomy within 12 weeks before the first screening visit, and with active malignancy were excluded from the study.

Response criteria for treatment were as follows: (a) complete remission (CR), platelet count ≥ 100 × 109/L measured on 2 occasions (at least 7 days apart), and the absence of bleeding; (b) partial response(PR), platelet count ≥ 50 × 109/L measured on 2 occasions (at least 7 days apart), and the absence of bleeding8; (c) no response, a platelet count < 50 × 109/L or a less than twofold increase in platelet count from baseline or the presence of bleeding2. Patient characteristics and other treatments used for thrombocytopenia and their dose were also noted. The baseline platelet counts, platelet counts change curves, time to response (TTR), duration of treatment, the CR and PR rate during treatment, and adverse effects of eltrombopag were also analyzed. The predictors for a response were analyzed using a univariate analysis such as Chi-square or nonparametric test (Table 3), including age, gender, protopathy, platelet reduction time, prior therapy, anemia, white blood cells (WBCs) counts, reticulocyte counts, level of complement, bone marrow features, and so on. A multiple correspondence analysis (MCA) of the association between variables corresponds to a cross-tabulation of categorical variables and a multidimensional scaling technique. The results of MCA were graphically presented in a 2-dimensional Euclidean space. This study was approved by Renji hospital ethics committee.

Statistical analysis

A descriptive statistical analysis was developed in Excel (Microsoft Corp). Normally and non-normally distributed continuous variables were respectively summarized as the median and interquartile range (IQR). Discrete variables were summarized as percentages. In order to identify predictors for response, we performed a univariate analysis such as Chi-square or nonparametric test of baseline variables between responder and non-responder of eltrombopag in patients with CTD-ITP. To visualize homogeneous clusters of patients with distinct response to eltrombopag, we included all baseline variables (Table 3) showing p-values < 0.1 in univariate analysis by MCA as previously described9,10. We stated that all methods were carried out in accordance with relevant guidelines and regulations.

Results

Patient characteristics

A total of 15 female patients with refractory CTD-ITP were enrolled in this study. There are 9 SLE patients, 3 SS patients, 3 patients diagnosed with UCTD. Only one patient was APS (tested positive for aPL and β2-GPI). Their median age at the time of inclusion was 40.6 years (IQR, 16–63 years). The median protopathy duration was 6.87 years (IQR, 0–31 years), the severe thrombocytopenia was 4.8 years (IQR, 0–16 years), and the median disease duration before the onset of severe thrombocytopenia was 2.07 years. In 13 patients, severe thrombocytopenia was the presenting manifestation of protopathy. The lowest platelet counts were less than 15 × 109 /L in all patients. All patients were refractory to a high dose of corticosteroids (at least 1 mg/kg day) and prior immunosuppressive treatment with thrombocytopenia, including cyclosporine A (86.7%, 13/15), IVIG (53.3%, 8/15), TPO (33.3%, 5/13), rituximab (13.3%, 2/15) and other therapy (e.g., azathioprine, cyclophosphamide, mycophenolate mofetil, hydroxychloroquine). Among 15 patients with CTD-ITP, only one patient was suffering from hepatitis B cirrhosis, splenomegaly, and hyperthyroidism; 1 patient had ovarian cancer. Among 9 patients with SLE, the disease activity of one patient was severe, while most of the patients were stable or mild as measured by systemic lupus erythematosus disease activity index (SLEDAI) score.

Bone marrow aspiration was performed in 11 patients, where 5 patients showed a typical ITP. Patient characteristics, prior immunosuppressive treatments, and bone marrow feature are summarized in Table 1.

Table 1 Patient characteristics.
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Efficacy of eltrombopag on refractory CTD-ITP

The median platelet count at initiation of eltrombopag was 11.53 × 109/L (IQR, 1–30 × 109); 12 (80%) patients had a baseline platelet count 15 × 109/L or less. All subjects received eltrombopag at a dose of 25 mg/day, except one patient who received 50 mg/day. Nearly all the patients (93.33%, 14/15) completed 4 weeks treatment with eltrombopag; one patient discontinued the treatment of eltrombopag for complete remission, while 3 patients discontinued as lacking efficacy after 4 weeks treatment. The baseline platelet counts before treatment and platelet counts change curves at each time point are shown in Fig. 1A.

Figure 1
figure 1

(A) The baseline platelet counts before treatment and platelet counts change curves at each time point during treatment with eltrombopag. (B) Total duration of treatment and time taken for response to therapy until August 2019. (C) The complete remission (CR) rate and overall response rate at each point during treatment with eltrombopag.

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The median duration of therapy was 21.2 weeks (2–104 weeks), and the median remission time was 3.42 weeks (1–12 weeks) (Fig. 1B). Most of the patients (80%, 12/15) reposed well to eltrombopag. As shown in Fig. 1C, the CR and overall response rate was 26.67% and 66.67% 4 weeks later, respectively. However, the CR and overall response rate decreased with time; the CR rate was 13.33%, and the overall response rate was 40% 6 months later. The severe adverse events were seldom, except in one patient who stopped taking eltrombopag 4 weeks later for severe oral ulcers. The treatment regimen, response, TTR, duration of eltrombopag, and adverse events are shown in Table 2.

Table 2 Treatment regimen, response, time to response, total duration of treatment and adverse events of the drug were analysed.
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Identification of predictive factors for eltrombopag

To investigate the predictive factors for eltrombopag in refractory CTD-ITP, we first compared baseline variables between responder and non-responder of eltrombopag in patients with CTD-ITP by univariate analysis. Some potentially baseline variables (defined as p-values < 0.1) for the efficacy of eltrombopag among patients with CTD-ITP were shown in Table 3, including protopathy (p = 0.071), WBCs counts (p = 0.004), levels of hemoglobin (p = 0.002), and characteristics of bone marrow findings (p = 0.01). To graphically represent the association of categorical variables in a 2-dimensional Euclidean space, we then performed a MCA based on the baseline clinical manifestations and laboratory findings. With a Cronbach's alpha of 0.905 and variance of 77.7% for the modeling, the dimension 1 (the horizontal axis) seemed to separate two distinct clusters with favorable or unfavorable factors for the use of eltrombopag in patients with refractory CTD-ITP. As shown in Fig. 2, medium to severe anemia, leukopenia, bone marrow aspiration showing aplastic anemia (AA), an absence of megakaryocytes or macrophage activation syndrome (MAS), and a protopathy with SS have been associated with the poor response to eltrombopag in patients with refractory CTD-ITP. While, patients with normal WBCs counts, no or slight anemia, and relative normal bone marrow aspiration have been associated with a good response to eltrombopag.

Table 3 Comparison of baseline variables between responder and non-responder of eltrombopag in patients with connective tissue disease-associated immune thrombocytopenia (CTD-ITP).
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Figure 2
figure 2

The multiple correspondence analysis (MCA) data for predictive factors for eltrombopag. Variables used in this analysis were anemia, white blood cells (WBCs) counts, bone marrow features, protopathy. For clarity, only the most discriminant variables are represented. AA aplastic anemia, MAS macrophage activation syndrome, SLE systemic lupus erythematosus, SS Sjogren's syndrome, UCTD undifferentiated connective tissue disease, ITP idiopathic thrombocytopenic purpura.

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Discussion

Eltrombopag is a thrombopoietin-receptor agonist (TPO-RA) that mimics the action of endogenous TPO on megakaryocytes and megakaryocyte precursors, promoting their growth and differentiation, thus, increasing platelet production11. In 2018, guidelines for ITP recommended TPO-RAs for patients who did not respond well to glucocorticoids or rituximab, or those with splenectomy12. In this study, we performed a real-world investigation of eltrombopag treatment for patients with CTD-ITP. Our results demonstrated that eltrombopag might be an effective therapy for patients with ITP secondary to autoimmune diseases who did not respond well to standard ITP treatment.

In this study, 80% of patients responded well to eltrombopag. Most of our patients received a dose of eltrombopag of 25 mg/day, which has been recommended for patients of East Asian descent. Eltrombopag was well tolerated, except for severe oral ulcers, which were observed in one patient. The median time taken for initial response to eltrombopag was 3.42 weeks, and peak response rate occurred after a one-month treatment. Many positive results in terms of effectiveness and maintained platelet response rate of eltrombopag have been reported in the treatment of chronic ITP13,14. Interestingly, we found that the response rate gradually declined until reaching the plateau stage. It might be related to the small dose of eltrombopag administrated on the CTD-ITP patients, and also the clinical severity of the primary disease for CTD-ITP. Indeed, several clinical trials observed the similar plateau phenomenon in more than half of robust responders of eltrombopag in refractory severe aplastic anemia15 or patients with chronic immune thrombocytopenia16. Furthermore, the effect of eltrombopag on cell proliferation rates may also have a plateau phenomenon17.

A number of studies have indicated that TPO-RAs is associated with thrombotic risk when treating patients with chronic liver disease and those having antiphospholipid antibodies (aPL)18,19,20,21,22. In our study, one patient had hepatitis B cirrhosis, and another one was aPL and β2-GPI positive; yet, no thromboembolic events were observed after 26 weeks and 16 weeks treatments, respectively.

Many ITP real-world studies evaluated clinical and laboratory variables associated with response to eltrombopag and the relative factors, including age, anemia, bone marrow features, and so on11. In our study, we found that anemia, decreased WBCs counts, bone marrow aspiration showing aplastic anemia, an absence of megakaryocytes or macrophage activation syndrome (MAS) were predictors of worse outcome. Bone marrow characteristics such as megakaryocytopenia, bone marrow hypocellularity, and dyserythropoiesis were predictors of worse outcome23. Eltrombopag is effective in ITP, aplastic anemia (AA), and myelodysplastic syndromes (MDS), which is probably due to a sort of spillover specificity on other growth factor receptors, as well as to the action at the stem-cell level11. On the whole, although responses are observed in MDS and AA, eltrombopag is more effective in classic ITP, confirming the importance of megakaryocytic reservoir23,24. Indeed, marrow megakaryocyte count could be a response predictor of severe thrombocytopenia in patients with SLE and SS25,26. However, more prospective studies are warranted to address whether SS-ITP patients have a poor response to eltrombopag than other CTD-ITP patients.

This study has a few limitations. First, the sample size was small. Second, because this is a retrospective study, possible recall and selection errors cannot be excluded.

Conclusions

Eltrombopag is effective and well-tolerated in CTD-associated thrombocytopenia. Some factors should be considered in the use of eltrombopag, including the disease of protopathy, blood test, and bone marrow aspiration. Additional large studies would be needed to confirm the results.