Evaluation of Bone Marrow Fibrosis and Lymphocyte Subsets in Adult Patients with Primary Immune Thrombocytopenia and Correlation with Clinical Findings

Immune thrombocytopenia (ITP) is a common autoimmune disorder characterized by low platelet counts that can lead to bleeding. Diagnosis of ITP is generally made by review of peripheral smear and evaluation of history and examination of the patient. Bone marrow examination is not diagnostic in patients with ITP and is performed only in those with other hematologic abnormalities and in those who do not have an adequate response to treatment.Bone marrow examinations in ITP have been investigated in studies dating back several decades. Some investigators have found megakaryocyte numbers to be increased . Meanwhile,other study have shown reticulin levels among adult patients with primary ITP may be elevated with respect to the general adult population. Morphological changes in ITP MKs include cytoplasmic vacuolization, reduction of granules, and smoothing of plasma membrane associated with increased number of MKs in BM. However, fibrosis appears to be no correlation with disease progression and the correlation with clinical outcome remains equivocal at best.The current study aimed to understand the marrow levels of reticulin and/or collagen fibres among adult patients-the majority with clinical features of primary ITP-at the time of diagnosis and to evaluate any correlation between fibrosis and primary ITP specific clinical features.

Results

1. Of the 282 newly diagnosedand chronic patients from October 2015 to November 2017 were enrolled into the study which 102 patients were newly diagnosed and 182 patients were chronic.Median age was 46 yr (range 18-85), with 108 males and 174 females. At diagnosis 229 (79%) patients were age 60 or younger and 62 (81.8%) were women. There were more females than males with no significant difference in age between genders. CD41⁺megakaryocyte numbers on bone marrow aspirates did not meet statistical significance, a trend that chronic group likely have more megakaryocyte numbers189(IQR 68-340) than newly diagnosed group143(IQR 70-309). The prevalence of a bone marrow grading greater than 0 among our sample of newly diagnosed and chronic ITP patients were 23.5% and 14.4%, but the difference was not statistically significant(P=0.063).

2. Comparing cases with BMF> 0 with those without (MF=0),the former showed increased bone marrow cellularity (P=0.022).In terms of changes in lymphocyte subsets, the percentage of CD19+B Lymphocyte and CD3-CD56+ NKLymphocyte in patients with bone marrow grading > 0 were obviously lower than those in bone marrow grading = 0[8 (4.1-12.4) vs 5.0 (3.6-8.8), P=0.008].The bone marrow fibrosis grade were inversely correlated with the percentage of CD3-CD56+ NK Lymphocyte(r=0.307, P=0.004). In a further analysis, a significant inverse correlation was present between the CD3-CD56+ NK Lymphocyte and bone marrow cellularity(r=0.432, P=0.008).

3. In newly diagnosed patients who had achieved R, the median (range) TTR was 5 days (6-14.5 days) in the bone marrow grading =0 group compared with 6 days (6-18 days) in bone marrow grading > 0 group (P =0.624). Notably, in chronic ITP patients ,MF> 0 cases more frequently required more therapies compared with bone marrow grading = 0 group 2 (range, 1-4) vs 4((range, 4-5) during the first year after diagnosis (P<0.01). twenty-seven (37.5%) of the newly diagnosed 72 patients were long-term responders.

4. Factors affecting response were assessed by univariate logistic regression, which indicated that CD3-CD56+NK Lymphocyte was independently associated with a higher response (P = 0.010; hazard ratio (HR)0.515, 95% CI 0.311-0.855). As for the factors affecting LTR, univariate logistic regression results in Table 4 showed that MF> 0 , CD19+B Lymphocyte and gender is a predictive factor for achieving LTR(0.009; hazard ratio (HR)0.789 , 95% CI 0.561-0.762).

As a conclusion, BM fibrosis is not rare in ITP patients,its incidence is actually higher than expected, as stated in literature. In this study, there were differences between ITP-associated MF and without MF in terms of number of re-treatment ,LTR, lymphocyte subsets in ITP. However, the TTR were no differences between ITP-associated MF and without MF patients.