Pure red cell aplasia may be acute or chronic. Chronic aplasia is either congenital (for example Blackfan-Diamond syndrome) or acquired (thymoma, systemic lupus erythematosus, autoimmune thyreoiditis).
Bone marrow is normocellular or only slightly hypocellular with normal megakaryocytes and normal myelopoiesis. Erythropoietic islands are missing, separate normoblasts are sparsly dispersed. Lymphocytosis and plasmocytosis are usually reactive, the number of mast cells and macrophages with abundant iron deposits is increased.