Bone marrow histology in patients with a paroxysmal nocturnal hemoglobinuria clone correlated with clinical parameters

Paroxysmal nocturnal hemoglobinuria (PNH) is a disease with variable presentation, including classical PNH (cPNH) and PNH with aplastic anemia (AA-PNH). Here, we describe bone marrow (BM) histology related to clinical findings in 67 patients with a PNH clone. Patients were divided in AA-PNH (n = 39) and cPNH (n = 28) based on clinical criteria and were compared to 17 AA patients without PNH clone. Median PNH clone size was higher in cPNH (75 %) than in AA-PNH (10 %) (p < 0.0001). BM cellularity was normal or increased in 65 % of cPNH, while it was decreased in AA-PNH and AA (95 % and 100 %) (p < 0.0001). Myelopoiesis and megakaryopoiesis were decreased in 85 % and 100 % of AA-PNH and 100 % of AA patients, but also in 86 % and 46 % of cPNH patients, even when peripheral blood values were normal. The percentage of CD59-deficient late-stage myeloid cells determined immunohistochemically correlated to PNH granulocyte clone size. Lymphoid nodules and increased mast cell numbers were present in all groups but more frequently in AA-PNH (38 % and 73 %) than in cPNH (20 % and 43 %). BM iron was decreased in 88 % of cPNH, while it was increased in AA-PNH (64 %) and AA (100 %) (p < 0.0001). Hemolysis was present in all cPNH but also in AA-PNH patients (67 %). In conclusion, cPNH patients had more cellular BM and more prominent erythropoiesis than AA-PNH patients. Nonetheless, cPNH patients also show AA features such as myeloid and megakaryocyte hypoplasia and inflammatory infiltrates, although more subtle than in AA-PNH. No significant differences were found between BM of AA patients with and without PNH clone.