1 Department of Nephrology, Gasthuisberg Hospital, Leuven, Belgium, 2 Department of Hematology Gasthuisberg Hospital, Leuven, Belgium
Case
A 49-year-old Caucasian female underwent a cadaveric renal transplantation in June 1999 because of end-stage renal failure secondary to autosomal dominant polycystic kidney disease, for which she had been treated with chronic haemodialysis since April 1996. Her medical history was otherwise unremarkable. She had never required substitution therapy with erythropoietin. No induction therapy was administered before transplantation. During the transplantation procedure the left native kidney was removed in order to make space for the transplant. The post-transplantation recovery was uneventful and she was discharged on day 14 with a haemoglobin of 9.2 g/dl and a serum creatinine of 1.94 mg/dl. The daily immunosuppressive regimen consisted of methylprednisolone 12 mg, tacrolimus 12 mg and mycophenolate mofetil 1000 mg twice daily. Serum tacrolimus levels were kept between 12 and 15 µg/l. Other medications included trimethoprim/sulfamethoxazole 800/160 mg and cimetidine 400 mg. Since the donor's serologic status was positive for cytomegalovirus (CMV), ganciclovir in an oral dose of 1000 mg daily was administered as a standard prophylactic measure.
Five weeks later she complained of increasing fatigue and drowsiness. Clinical examination was unremarkable. Laboratory examination revealed a severe, slightly macrocytic anaemia with a haemoglobin level of 5.6 g/dl together with leucopenia and thrombo- penia, 2500/mm3 and 89 000/mm3 respectively. Reticulocytosis was 0.2%. Renal function was stable and serum creatinine was 1.46 mg/dl. A bone marrow biopsy was performed, showing normal myeloid and megakaryocyte cell lines, a very poorly represented erythroid cell line with pronounced megaloblastic properties, and the occurrence of giant pronormoblasts; in some of these, unclear inclusions were noted (Figure 1). Vitamin B12 levels in serum were <75 µg/l (normal value 170800), folate and iron levels were normal. Serum parvovirus B19 antibodies, both IgG and IgM were negative. Buffy coats for CMV were repeatedly negative. Intramuscular vitamin B12 substitution therapy was started together with transfusion of 4 U of packed cells. The patient was discharged with a haemoglobin level of 11.0 g/dl. Over the next 4 weeks, however, the anaemia relapsed with haemoglobin falling to 5.5 g/dl and still extremely low reticulocytosis (0.1%), this despite adequate vitamin B12 substitution.
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Question
What is the diagnosis? What is the treatment of choice?
Answer to the quiz on the preceding page
The aplastic anaemia in our patient was caused by parvovirus B19 infection. Serum antibody detection, both IgG and IgM was negative on repeated occasions. However, direct detection of the S gene and the NS gene of parvovirus B19 by the PCR method was positive, both in serum and in bone marrow.
Vitamin B12 deficiency cannot have caused the anaemia, since adequate substitution therapy, as reflected by normal serum values did not result in recovery of the anaemia nor in normalization of the bone marrow abnormalities.
A few cases of severe anaemia in transplant recipients receiving tacrolimus have been reported, but in a multicentre study with FK506 in liver transplant recipients no haematopoietic side-effects were reported [1]. Moreover, parvovirus B19 DNA detection was not performed in these cases.
Mycophenolate mofetil is a selective blocker of the ribose-derived purine synthesis pathway, which in theory should not have major repercussions on erythropoiesis. However, van Besouw et al. recently reported that the administration of mycophenolate mofetil can lead to a mild to moderate decrease of haemoglobin. This effect was encountered in patients receiving a dose of 2 g/day, and disappeared with a daily dose of 1 g [2]. The discontinuation of mycophenolate mofetil in our patient failed to correct the anaemia, ruling out a causal relationship.
In addition to her immunosuppressive regimen, our patient received ganciclovir 1000 mg daily as prophylactic regimen for CMV infection. Neutropenia (<1000/mm3) and thrombocytopenia (<50 000/mm3) are well-known side-effects of ganciclovir, occurring in approximately 40 and 15% of patients respectively. Anaemia is also a common feature with an occurrence of 6.7% [3]. The clinical presentation with predominant anaemia and only mild thrombocytopenia and neutropenia is highly atypical for ganciclovir. Moreover, as in the case of mycophenolate mofetil, the anaemia persisted after discontinuation of the drug.
Several viruses, such as hepatitis B and C, herpetoviridae and parvovirus B19 can cause aplastic anaemia. Normal serologic tests and the absence of typical clinical and laboratory features easily ruled out these pathogens, leaving parvovirus B19 as the probable cause, as confirmed by the presence of viral DNA in serum and bone marrow. Parvovirus B19 is the only representative of the parvovirus group known to cause illness in humans. Owing to the high level of cell tropism, the virus can replicate in proliferating and differentiating erythroid precursors and consecutively cause red cell aplasia by inducing red cell precursor apoptosis. After binding to the erythrocyte P-antigen, its cellular membrane ligand, the virus causes apoptosis of erythrocyte progenitors via the NS1-caspase pathway with a subsequent arrest in erythropoiesis [46].
In normal individuals, after the appearance of specific IgM antibodies, the virus is rapidly cleared and erythropoiesis resumes after 710 days, leaving the aplastic episode unnoticed. However, when an underlying haemolytic disorder is present, such as sickle cell anaemia, a deep aplastic crisis can result. In patients with immune disorders, such as HIV, haematological malignancy and organ transplant recipients, the clearance of parvovirus B19 can be inadequate, resulting in viral persistence and chronic aplastic anaemia. In renal transplant recipients, 13 cases (including ours) of aplastic anaemia due to parvovirus B19 infection have been reported so far. In 11 cases, diagnosis was established by detection of IgM antibodies directed against the virus. In only two cases, including ours, IgG and IgM antibodies were negative, but diagnosis was established by viral DNA detection in serum and bone marrow [7].
Since parvovirus B19 antibodies are highly prevalent in the normal population, with seroprevalence reaching 80100% at the age of 70, diagnosis based on serology alone can be difficult. On the other hand, as demonstrated by our quiz patient, a negative antibody status does not rule out infection in transplant recipients, especially in view of the trend to more potent immunosuppressive regimens, often including three different agents. Therefore, parvovirus B19 DNA detection on serum and bone marrow by the PCR technique should be carried out whenever parvovirus infection is suspected, since it is a treatable and possibly underestimated cause of anaemia in the immunocompromised host, that can be missed by serology alone. Parvovirus B19 infection can theoretically be treated by reducing immunosuppression. Some authors found tacrolimus to have an important role in defective parvovirus B19 clearance and report recovery by switching tacrolimus to cyclosporin A [8]. When reducing or switching immunosuppression is unsuccessful, administration of intravenous immunoglobulin is the treatment of choice. The probable mechanism involves passive immunization, since high parvovirus B19 antibody titres have been demonstrated in commercial immunoglobulin preparations [9]. Several therapeutic regimens have been proposed, ranging from 0.5 g/kg during 2 days to 0.4 g/kg during 10 days [9].
Returning to our patient, reduction of immunosuppression by cessation of mycophenolate mofetil did not result in recovery of the anaemia. Treatment consisted of intravenous administration of immunoglobulins in a daily dose of 0.4 g/kg for 5 consecutive days. From day 4 onwards, our patient started to complain of bilateral hip and sternum pain. This was followed by a dramatic reticulocytic response from day 5 onwards, with relative reticulocytosis of 10.1% on day 10. Four weeks later, haemoglobin levels had increased to 13.6 g/dl, this without transfusion or administration of erythropoietin.
Notes
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References