The pathophysiology of pure red cell aplasia: implications for therapy.

To determine the utility of marrow culture in defining the natural history and therapeutic response of pure red cell aplasia we have studied 37 patients. Patients were evaluated at the University of Washington before specific therapies (n = 21) or at the time of treatment failure in = 16). Evaluation included a medical and drug exposure history, a physical examination, a chest x-ray or computed tomography to rule out thymoma, lymphocyte immunophenotype studies, anti-nuclear antibody and rheumatoid factor determinations, marrow cytogenetics, and marrow progenitor cell cultures. Retrospective Southern analyses to detect human parvovirus B19 was performed in the 27 patients for whom sera was stored. Clinical follow-up was obtained to document therapeutic responses. Normal burst forming unit-erythroid (BFU-E) growth (>30 bursts/10(5) marrow mononuclear cells [MMNC]) in culture proved an outstanding predictor of clinical response, as 27 of 29 individuals with normal frequencies of erythroid bursts in culture responded to immunomodulating therapies (sensitivity 96%, specificity 78%, predictive value 93%, P = .0001 with two-tailed chi square analysis). Overall, 28 patients responded to either immunomodulating therapies or drug withdrawal. Twenty-four patients obtained a normal hematocrit (complete response [CR] and 4 additional patients became transfusion independent (partial response). Although responding patients often required several therapies, 20 of 24 (83%) patients who obtained a CR have sustained a normal hematocrit without maintenance therapy at the time of last follow-up (median 5 years). In contrast, of 8 patients with poor in vitro BFU-E growth (<6 bursts/10(5) MMNC), 7 failed to respond to any therapy and all died (median survival time 17 months). Our data suggest that in individuals, from whom BFU-E mature appropriately in culture, immunosuppressive drugs should be used sequentially until a CR is obtained and a durable remission is the expected outcome.