Hydroxyurea-associated Platelet Count Oscillations in Polycythemia Vera: A Report of Four New Cases and a Review

The highs and lows of cyclic thrombocytopenia

Cyclic thrombocytopenia (CTP) is characterized by periodic platelet oscillation with substantial amplitude. Most CTP cases have a thrombocytopenic background and are often misdiagnosed as immune thrombocytopenia with erratically effective treatment choices. CTP also occurs during hydroxyurea treatment in patients with myeloproliferative diseases. While the aetiology of CTP remains uncertain, here we evaluate historical, theoretical and clinical findings to provide a framework for understanding CTP pathophysiology. CTP retains the intrinsic oscillatory factors defined by the homeostatic regulation of platelet count, presenting as reciprocal platelet/thrombopoietin oscillations and stable oscillation periodicity. Moreover, CTP patients possess pathogenic factors destabilizing the platelet homeostatic system thereby creating opportunities for external perturbations to initiate and sustain the exaggerated platelet oscillations. Beyond humoral and cell-mediated autoimmunity, we propose recently uncovered germline and somatic genetic variants, such as those of MPL, STAT3 or DNMT3A, as pathogenic factors in thrombocytopenia-related CTP. Likewise, the JAK2 V617F or BCR::ABL1 translocation that drives underlying myeloproliferative diseases may also play a pathogenic role in hydroxyurea-induced CTP, where hydroxyurea treatment can serve as both a trigger and a pathogenic factor of platelet oscillation. Elucidating the pathogenic landscape of CTP provides an opportunity for targeted therapeutic approaches in the future.

How I manage cyclic thrombocytopenia

Cyclic thrombocytopenia (CTP) is a rare disease, which is characterized by periodic fluctuation of the platelet count. The pathogenesis of CTP is unknown and most likely heterogeneous. Patients with CTP are almost always misdiagnosed as having primary immune thrombocytopenia (ITP). The interval between ITP and CTP diagnosis can be many years. CTP patients often receive ITP-specific therapies including corticosteroids, thrombopoietin receptor agonists, rituximab, and splenectomy, which are followed by a transient increase in platelet count that is wrongly attributed to treatment effect with inevitable "relapse." CTP can be diagnosed by frequent platelet count monitoring, which reveals a typical pattern of periodic platelet cycling. An early diagnosis of CTP will prevent these patients from being exposed to possibly harmful therapies. The bleeding phenotype is usually mild and consists of mucocutaneous bleeding at the time when the platelet count is at its nadir. Severe bleeding from other sites can occur but is rare. Some patients respond to cyclosporine A or to danazol, but most patients do not respond to any therapy. CTP can be associated with hematological malignancies or disorders of the thyroid gland. Nevertheless, spontaneous remissions can occur, even after many years.

Thrombopoietin Contributes to Extreme Thrombocytosis After Pediatric Pancreatectomy With Islet Autotransplantation

OBJECTIVE

This study aims to explore the role of thrombopoietin (TPO) production in extreme thrombocytosis that is often observed after pancreatectomy with islet autotransplantation (IAT) and the effectiveness of hydroxyurea in thrombocytosis management.

METHODS

Retrospective chart review was performed for all patients who underwent pancreatectomy with IAT at our institution between April 1, 2015, and December 31, 2016. Data evaluated included demographics, platelet counts, TPO levels, and thrombocytosis management strategies.

RESULTS

Twelve total and 1 subtotal pancreatectomy with IAT cases were reviewed. All operations included splenectomy. No major surgical or thrombotic complications occurred. Thrombopoietin levels, normal preoperatively, rose significantly (median, 219 pg/mL) soon after surgery, peaking on median postoperative day 3. Platelet counts, also normal preoperatively, increased within a week of surgery, with 92% over 1000 K/μL (median peak platelet count, 1403 K/μL). Platelet counts and TPO levels dropped after hydroxyurea initiation in most patients.

CONCLUSIONS

After pancreatectomy with IAT, patients experienced marked TPO rise and subsequent thrombocytosis, and both decreased significantly after hydroxyurea initiation. These data suggest that TPO elevation and associated increased platelet production may be one driver of early extreme post-total pancreatectomy with islet autotransplantation thrombocytosis, and this process may be modulated by hydroxyurea.

Oscillatory haematopoiesis in adults with sickle cell disease treated with hydroxycarbamide

Hydroxycarbamide therapy has been associated with significant oscillations in peripheral blood counts from myeloid, lymphoid and erythroid lineages in patients with polycythaemia vera and chronic myeloid leukaemia. We retrospectively evaluated serial blood counts over an 8-year period from 44 adult patients with sickle cell disease receiving hydroxycarbamide. Platelet counts, leucocyte counts, haemoglobin values and reticulocyte counts, apportioned by hydroxycarbamide status, were analysed using a Lomb-Scargle periodogram algorithm. Significant periodicities were present in one or more counts in 38 patients receiving hydroxycarbamide for a mean duration of 4·81 years. Platelet and leucocyte counts oscillated in 56·8% and 52·3% of patients, respectively. These oscillations generally became detectable within days of initiating therapy. During hydroxycarbamide therapy, the predominant periods of oscillation were 27 ± 1 d for platelet counts and 15 ± 1 d for leucocyte counts. Despite an absolute decrease in leucocyte and platelet counts during hydroxycarbamide treatment, the amplitudes between nadirs and zeniths remained similar regardless of exposure. Our observations appear consistent with previously proposed models of cyclic haematopoiesis, and document that hydroxycarbamide-induced oscillations in blood counts are innocuous phenomena not limited to myeloproliferative disorders as described previously. We speculate the known cell cycle inhibitory properties of hydroxycarbamide may accentuate otherwise latent constitutive oscillatory haematopoiesis.

Progenitor cell self-renewal and cyclic neutropenia

OBJECTIVES

Cyclic neutropenia (CN) is a rare genetic disorder where patients experience regular cycling of numbers of neutrophils and various other haematopoietic lineages. The nadir in neutrophil count is the main source of problems due to risk of life-threatening infections. Patients with CN benefit from granulocyte colony stimulating factor therapy, although cycling persists. Mutations in neutrophil elastase gene (ELA2) have been found in more than half of patients with CN. However, neither connection between phenotypic expression of ELA2 and CN nor the mechanism of cycling is known.

MATERIALS AND METHODS

Recently, a multicompartment model of haematopoiesis that couples stem cell replication with marrow output has been proposed. In the following, we couple this model of haematopoiesis with a linear feedback mechanism via G-CSF.

RESULTS

We propose that the phenotypic effect of ELA2 mutations leads to reduction in self-renewal of granulocytic progenitors. The body responds by overall relative increase of G-CSF and increasing progenitor cell self-renewal, leading to cell count cycling.

CONCLUSION

The model is compatible with available experimental data and makes testable predictions.

Idiopathic cyclic thrombocytopenia

Cyclic thrombocytopenia (CTP) is an uncommon disorder characterized by periodic fluctuations in platelet counts, typically resulting in episodes of thrombocytopenia alternating with normal platelet counts. While some CTP cases are associated with a primary hematologic disease, most are idiopathic. Patients with CTP are frequently misdiagnosed as idiopathic thrombocytopenic purpura (ITP) because CTP has clinical features very similar to ITP. When evaluating patients with suspected ITP, CTP should always be included in the differential diagnoses because CTP generally does not respond to standard ITP treatments, including corticosteroids, splenectomy, and intravenous immunoglobulin. Two clinical features relatively unique to CTP besides periodic thrombocytopenia are rebound thrombocytosis unrelated to recent splenectomy and platelet nadirs occurring during menses. When a diagnosis of CTP is made, patients must be offered a period of observation, as many may not require treatment. If treatment is clinically indicated, the literature suggests that hormonal therapy provides the best response.

Modern treatment strategies in polycythemia vera

Polycythemia vera (PV), one of the chronic myeloproliferative disorders (MPD), is characterized by predominant erythroid proliferation and secondary platelet proliferation, and by progression from a proliferative stage to a metastatic phase and finally a malignant phase. These characteristics expose patients to increased risk for thrombohemorrhagic complications, myeloid metaplasia, myelofibrosis, and acute leukemic conversion irrespective of treatments. Currently, there are three agents-hydroxyurea (HU), interferon-alfa (IFN-alpha), and anagrelide-that differ in mechanisms of action and in treating specific phenotypic manifestations of PV, suggesting a potential role for combination therapy. They also differ widely in side effects profiles and severity. Because of the differing risks for long-term complications associated with these agents, age is an important variable in selecting treatments. Patients at high risk for thrombohemorrhagic complications all require cytoreduction, as do patients at intermediate risk who are not effectively managed by phlebotomy and low-dose aspirin. In younger patients, the safest and most effective combination treatment appears to be anagrelide plus IFN-alpha, while in older patients anagrelide plus hydroxyurea may be effective. HU is used sparingly in younger patients because of the long-term increased risk of mutagenicity and possibly leukemogenesis. IFN-alpha is particularly indicated for patients with myeloid metaplasia evidenced by splenomegaly. Anagrelide, which acts on the mature megakaryocyte to prevent platelet budding, is uniquely efficacious in the control of platelet counts.