Introduction

Pure white cell aplasia (PWCA) is a rare hematological disease [1] with an unknown incidence rate. As far as we know, there are only 20 cases of PWCA that have been reported in 10 literature. PWCA is characterized by agranulocytosis in the peripheral blood and is associated with a profound suppression of entire granulopoiesis in bone marrow (BM), whereas erythropoiesis and megakaryocytopoiesis remain intact [2]. The detailed pathogenesis of PWCA is unclear; however, an association with the inhibitory activity of immunoglobulins on granulopoiesis has been reported [2,3,4]. The association of PWCA with thymoma has also been described [5]. No treatment protocols for PWCA have yet been established. Here, we describe the successful treatment of a patient with PWCA accompanied with thymoma using cyclosporine A (CyA) followed by thymectomy.

Case report

A 63-year-old male experienced temporal agranulocytosis after a viral infection in May 2 years ago of admission to the hospital. His medical history was unremarkable. Three days prior to admission, the patient had developed fever and had been initiated on an oral antibiotic (400 mg of garenoxacin, once daily) by his primary care physician. However, the fever did not improve, and he was admitted to our hospital.

Laboratory blood test results revealed neutropenia (Table 1). The patient’s renal function and coagulation tests were within normal limits. Additionally, his immunoglobulin levels were low (Table 1), and he was negative for anti-nuclear and anti-neutrophil antibodies. Flow cytometric analysis did not detect T/B-cell monoclonal expansion, and no monoclonal rearrangements of the T-cell receptors were evident in peripheral blood. Further tests for hepatitis B and C viruses, Lyme disease, Epstein–Barr virus, cytomegalovirus, Mycoplasma, Chlamydia, Ehrlichia, tuberculosis, and human immunodeficiency virus in serum and bacterial cultures from blood and urine were negative. BM aspiration revealed a normocellular marrow without granulocytes (Table 1). Flow cytometry of the BM aspirate and peripheral cells did not show any evidence for T- or B-cell monoclonality. Lymphocyte subsets were also normal in the peripheral blood and BM. Karyotypes of BM cells appeared normal. Chest X-ray and computed tomography revealed evidence of thymoma (Fig. 1). Based on laboratory and imaging results, the patient was diagnosed with PWCA associated with thymoma, and treatment with granulocyte colony-stimulating factor (G-CSF; filgrastim, 5 µg/kg/day) was initiated on the day of admission to the hospital. However, there was no improvement in the neutrophil counts after 4 days of G-CSF, and BM aspiration did not show any improvement in myelopoiesis after 10 days of G-CSF administration. Therefore, CyA (150 mg/day for three consecutive days) was added 10 days after initiation of G-CSF administration. BM reexamination 13 days after the start of CyA treatment confirmed that normal granulopoiesis had resumed. An increase in neutrophil counts to normal levels occurred following treatment, accompanied by normalization of body temperature and C-reactive protein levels. Laboratory data including BM examination were almost normal 3 months later (Table 1), at which time thymectomy was performed, and CyA treatment was suspended. At the time, laboratory values including BM examination were almost normal (Table 1). Histopathology of the thymectomy specimen revealed benign spindle-cell thymoma. The patient has been in complete remission for over 4 years (Fig. 2).

Table 1 Laboratory data
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Fig. 1
figure 1

Chest X-ray and computed tomography images demonstrating a large thymic lesion (triangle)

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Fig. 2
figure 2

Evolution of granulocyte counts with treatment in our patient

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An in vitro colony-forming unit (CFU) granulocyte–macrophage (CFU-GM) assay was performed in triplicate using normal human mononuclear cells in a methylcellulose-based semisolid culture medium (MethoCult H4434; STEMCELL Technologies, Vancouver, BC, Canada), containing various concentrations [0% (control normal serum only), 5%, 10%, and 20%] of patient serum for 14 days. As shown in Fig. 3, severe suppression of CFU-GM colonies was observed in the presence of 20% patient serum, suggesting the presence of a CFU-GM inhibitor in the patient’s serum.

Fig. 3
figure 3

In vitro CFU-GM assay in the presence of various concentration of patient serum, demonstrating the suppressive effect of the patient serum on colony formation. The number of CFU-GM colonies using normal bone marrow mononuclear cells was significantly reduced with 20% patient serum

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Discussion

Several mechanisms have been suggested to underlie the pathogenesis of PWCA, such as autoimmunity, drug treatment, and viral infections [1, 2, 6, 7]. In this patient, severe neutropenia and complete lack of granulocytic series in BM were observed 3 days after the initial dose of antibiotics (garenoxacine). We believed that the occurrence of drug-induced agranulocytosis was less likely in 3 days. Specific CFU-GM suppression factors have also been speculated in the pathogenesis of PWCA. In some cases, immunoglobulin G specific for a transiently expressed antigen on immature myeloid cells was proposed to act as a suppressant leading to neutrophil destruction [3, 4]. Our results from the in vitro CFU-GM assay also suggested the presence of suppressive factor(s) in our patient’s serum. The reported efficacy of treatment approaches for PWCA, such as high-dose gamma globulins, plasmapheresis, and antibody therapy, to suppress B-cell activity [8, 9] suggests the involvement of humoral immune responses in the pathogenesis of PWCA. However, the transient effect of treatment and relapse of the disease during the course of such treatments were also reported. Thus, treatment against the humoral immune response might not be sufficient for sustained remission of PWCA.

PWCA is accompanied with thymoma in some cases, and the efficacy of thymectomy in PWCA was reported in several reports [8, 10,11,12,13], suggesting the involvement of thymoma as a pathogenic mechanism in PWCA. As the thymus selects functional, self-tolerant T-cells in a major histocompatibility complex/human leukocyte antigen-dependent manner, thymectomy in PWCA patients might compromise the reactivity and specificity of the selected T-cell repertoire [14]. Thus, deregulation of T-cell immune function might also be involved in the pathogenesis of PWCA in patients with thymoma.

The efficacy of CyA, which has immunosuppressive effects on T-cells, was also reported in the treatment of PWCA and Pure red cell aplasia [10, 15, 16]. CyA and thymectomy, which both might impact the deregulated T-cell function, were effective in our patient with thymoma and PWCA, who might have had suppressive factors circulating in his serum. Thus, these treatment options might also indirectly impact humoral immune responses, probably through a direct effect on the cellular immune responses.

In conclusion, the current case suggested that both the cellular and the humoral immune responses might be involved in the pathogenesis of PWCA in patients with thymoma. Thymectomy followed by CyA might be a useful treatment option that can induce prolonged complete remission in these patients.