Thrombopoietin and erythropoietin levels in idiopathic thrombocytopenic purpura and iron-deficiency anaemia

[Thrombocytopenia associated with iron deficiency: a rare differential diagnosis of auto-immune thrombocytopenic purpura]

INTRODUCTION

Iron deficiency is typically associated with microcytic anemia and thrombocytosis. It is a very uncommon cause of thrombocytopenia.

CASE REPORT

A 17-year-old female presented with marked fatigue and dyspnea on exertion. Review of systems was only remarkable for abundant menstruations during the past two years. The hemogram revealed a profound microcytic anemia (4.4 g/dL, mean corpuscular volume [MCV] 49 fL) and a thrombocytopenia (33 G/L). Marked iron deficiency was also present: ferritinemia <3 μg/L. Investigations did not find any cause of iron deficiency anemia other than excessive menstrual loss. Bone marrow examination showed an increase number of megakaryocytes, compatible with an immune thrombocytopenia purpura. Iron supplementation completely normalized the platelet count within 48 hours.

CONCLUSION

Iron affects thrombopoiesis. Because the number of megakaryocytes may then increase in the bone marrow, "iron deficiency thrombocytopenia" may be falsely diagnosed as immune thrombocytopenic purpura, leading to inappropriate corticosteroid therapy. Iron supplementation is the appropriate treatment of iron deficiency thrombocytopenia and allowed a rapid correction of the platelet count in all the 24 cases that have been previously reported with sufficient detail to be analyzed in the literature.

Complement-dependent cytotoxic factor to megakaryocyte progenitors in sera from patients with idiopathic thrombocytopenic purpura

The influence of sera from patients with idiopathic thrombocytopenic purpura (ITP) was examined on colony formation from megakaryocyte (M) progenitors. Though incubation of marrow cells in Iscove's modified Dulbecco's medium (IMDM) containing 50% sera from several ITP patients stimulated M-colony formation in 8 of 13 cases, incubation in the sera from the patients and in baby rabbit serum as a source of complement significantly suppressed the colony formation. Experiments showed that sera of immunoglobulin G from ITP patients had significant complement-dependent cytotoxicity to M-progenitors in normal marrow cells or in the marrow cells from corresponding patients, but not to CFU-e, BFU-e or CFU-gm. Cytospin preparations of individually collected M-colonies from marrow cells treated with ITP patients' sera and complement revealed a reduction of megakaryocyte colonies containing cells of multilineages. These results indicate that autoantibodies detected in ITP patients can bind not only to platelets and megakaryocytes, but may also bind to M-progenitors.

Apparent heterogeneity of human megakaryocyte colony- and thrombopoiesis-stimulating factors: studies on urinary extracts from patients with aplastic anaemia and idiopathic thrombocytopenic purpura

Megakaryocyte colon-stimulating factor (MEG-CSF) in the urinary extracts from patients wit aplastic anaemia (AA) revealed two distinct peaks of activity on Sephadex G-200 gel filtration with apparent molecular weights of 155,000 and 76,000. Both fractions induced significant thrombocytosis in peripheral blood and megakaryocytosis in the spleen of rats. Heterogeneity of MEG-CSF was also found in the extracts from the urine of patients with idiopathic thrombocytopenic purpura. The higher molecular weight MEG-CSF was significantly reduced when the gel filtration was performed under the dissociating conditions. Ion-exchange chromatography indicated that the higher molecular weight MEG-CSF had a different charge from the lower molecular weight MEG-CSF. These results suggest that the apparent heterogeneity of MEG-CSF is due to interaction of MEG-CSF with other proteins in the urinary extracts.

Thrombopoiesis- and megakaryocyte colony-stimulating factors in the urine of patients with idiopathic thrombocytopenic purpura

The urinary extract from patients with severe, chronic idiopathic thrombocytopenic purpura (ITP) was capable of inducing significant thrombocytosis in rats in vivo and enhancing megakaryocyte colony formation in culture of mouse bone marrow cells. The apparent specific activity of megakaryocyte colony stimulating factor (MEG--CSF) in the ITP extract was approximately one-half of that of the urinary extract from patients with aplastic anaemia (AA). Daily injections of ITP extract did not cause an increase in Hb concentration, while rats receiving AA urinary extract revealed profound erythropoiesis 3 weeks later. In vitro assay of erythropoietin (EPO) failed to show significant EPO activity in the extract from patients with ITP. These findings excluded the possibility that the observed activities of thrombopoiesis-stimulating factor (TSF) and MEG--CSF in the ITP urinary extract are due to contaminating EPO. Urine of patients with severe ITP appears to be a good source of TSF and MEG--CSF.

Isotope bioassay for "thrombopoietin"

An assay system has been developed in mice for the humoral agent "thrombopoietin." This is based on utilization in newly-formed platelets of the radio-amino-acid (75)Se selenomethionine 24 hours after intravenous injection. The possibility that the results could be due to the effects of species antibody, to foreign protein, or to an effect primarily on selenomethionine metabolism, has been explored, but the findings are consistent with the presence of a physiological humoral factor. Thrombopoietin has been shown to be present in the plasma of patients suffering from severe thrombocytopenia of varied aetiology.

Measurement of thrombopoiesis in rabbits using 75selenomethionine

Incorporation of (75)selenomethionine ((75)SeM) has been used to study platelet production in rabbits. Radioactivity of platelets was low after the intravenous administration of (75)SeM and rose to a maximum approximately 3 days after administration. Platelet radioactivity was independent of concurrent plasma levels. The life span of rabbit platelets, as estimated with this technique, was 4-5 days. In vivo reutilization of (75)SeM previously incorporated into plasma proteins was not detected. In vitro incorporation of (75)SeM by platelets in platelet-rich plasma was not demonstrated. Acute hemorrhage 24 hr before administration of (75)SeM increased the incorporation of (75)SeM into platelets. Transfusion-induced thrombocytosis reduced the incorporation of (75)SeM to approximately 30% of that observed in control animals. Suppression of bone marrow function with nitrogen mustard resulted in decreased numbers of platelets in the circulation, and a decrease in incorporation of (75)SeM. Delayed appearance of (75)SeM was observed in circulating platelets during recovery from marrow suppression. Injection of 75-225 ml of plasma from thrombocytopenic donors into normal rabbits increased incorporation of (75)SeM into platelets while normal plasma did not have this effect. The rate of appearance of (75)SeM in circulating platelets appears to provide a sensitive and specific method for the study of production of platelets by megakaryocytes. The data suggest more rapid entry of platelets into the circulation, and a sustained increase in incorporation of (75)SeM into platelet protein after stimulation of platelet production. The results are consistent with the concept of a humoral agent (thrombopoietin) that acts on megakaryocytes to regulate platelet production.