Bone Marrow Reticulin and Collagen Content in Patients with Adult Chronic Immune Thrombocytopenic Purpura: a Danish Nationwide Study

We quantified and differentiated reticulin and collagen content in bone marrow specimens from chronic immune thrombocytopenic (ITP) patients and examined the correlation between some clinical characteristics and the fibrosis grading. Through the Danish National Patient Registry, we identified 378 patients with chronic ITP from 1997 until 2007. Of these, 253 (67%) had undergone at least one bone marrow biopsy, and we retrieved the bone marrow specimens from 187 (74%). We graded the bone marrow content of reticulin and collagen according to the Thiele scale (Grade 0-3). We also retrieved information on patients' clinical characteristics. We examined the prevalence of bone marrow fibrosis grading > 0 by patients' age (≤ 75 years and > 75 years), sex, platelet count at baseline (< 30 × 10⁹/L, and ≥ 30 × 10⁹/L), splenomegaly, hepatomegaly, and medications. In total 75 chronic ITP patients (40%) had a bone marrow grading >0. Of these, 72 (39%) had Grade 1 reticulin fibers present. Only three patients (< 2%) had collagen fibers present: two had Grade 2 and one had Grade 3. The prevalence of bone marrow grading > 0 was lower in patients aged > 75 years than ≤ 75 years (prevalence ratio = 0.64, 95% CI: 0.36-1.15) and lower in men than women (prevalence ratio = 0.70, 95% CI: 0.45-1.09), while a baseline platelet count ≥ 30 × 10⁹/L was associated with a higher prevalence of grading > 0 (prevalence ratio = 1.24, 95% CI: 0.81-1.86). Thus, bone marrow reticulin and collagen content in chronic ITP patients may be associated with some clinical characteristics.