Pure red cell aplasia (PRCA): Response of three patients of cyclophosphamide and/or antilymphocyte globulin (ALG) and demonstration of two types of serum IgG inhibitors to erythropoiesis

Three cases of adult pure red cell aplasia (PRCA) ARE REPORTED. All patients proved refractory to various combinations of androgens and corticosteroids. The first case, harboring a thymoma, showed a complete clinical remission following cyclophosphamide therapy. The second and third responded similarly to either a combined cyclophosphamide + antilymphocyte globulin (ALG) treatment or to ALG administration preceded by a small dosage of cyclophosphamide, which had proved ineffective when administered alone. Serum IgG inhibitors to erythropoiesis were demonstrated in all cases by means of in vivo and/or in vitro techniques. The inhibitor(s), although directed against the erythroid marrow in both the first and third patients (PRCA type A), apparently functioned as an antibody to circulating erythropoientin (Ep) in the second case (PRCA type B). The inhibitor(s) was always absent in postremission samples. Additionally, experimental models for both types of human PRCA were established in normal rodents. The present studies support the contention that adult PRCA is an autoimmune disease. The therapeutic role of cytotoxic-immunodepressive agents in PRCA patients is confirmed. It is emphasized that ALG may represent an additional therapeutic tool in cases resistant to cyclophosphamide and/or steroids. In addition, cyclophosphamide proved effective in a patient harboring a thymoma not amenable to surgery. Finally, it is postulated that IgG serum autoantibodies, directed against either an early erythroid precursor (PRCA type A) or, more rarely, circulating Ep (PRCA type B), play a major role in the pathogenesis of the disease.