Gastroenterology/Hepatology Section and the Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, and the University of Washington School of Medicine, Seattle, WA, USA

Correspondence to: Dr G B McDonald, Gastroenterology/Hepatology Section (D2-190), Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, PO Box 19024, Seattle, WA 98109-1024, USA

Patients who develop veno-occlusive disease (VOD) of the liver may have low plasma levels of the natural anticoagulants protein C and antithrombin III, but large vessel thromboses are not commonly reported in these patients. We reviewed the records of 1847 consecutive patients for evidence of portal vein thrombosis. Eight patients (0.4%) developed portal vein thrombosis (PVT) at a median of day +28 (range 3-58). All patients had clinical evidence of VOD with ascites, a median total serum bilirubin 11.9 mg/dl, and median weight gain from baseline of 7.9%. Median plasma levels of antithrombin III and protein C were low (36% and 21%, respectively). Four patients with PVT died of severe VOD and multi-organ failure, but PVT did not contribute to death. We conclude that PVT is a rare complication of hematopoietic cell transplant and is associated with hepatic VOD. We speculate that PVT resulted from diminished portal venous flow (related to hepatic sinusoidal obstruction to blood flow) and a hypercoagulable state (related to low circulating antithrombin III and protein C levels). Prognosis depended on the severity of the underlying VOD and not PVT per se, suggesting that treatments directed solely toward dissolution of portal vein thrombi should be used with caution in this setting.

Bone Marrow Transplantation (2002) 29, 329-333. DOI: 10.1038/sj/bmt/1703368

portal vein thrombosis; veno-occlusive disease; protein C; antithrombin III; hematopoietic cell transplantation; thrombolytic therapy

Portal vein thrombosis (PVT) is a known complication of cirrhosis, neoplasm, intra-abdominal infection, and myeloproliferative disorders.¹ Recently, both acquired and inherited hypercoagulable forms of protein C deficiency,² antithrombin III deficiency³ and factor V Leiden⁴ have been reported as risk factors for PVT. Decreased levels of the naturally occurring anticoagulants protein C and antithrombin III have been observed in patients undergoing hematopoietic cell transplantation, usually after the development of veno-occlusive disease (VOD) of the liver,^5,6,7 although a cause-effect relationship between decreased plasma levels of protein C and antithrombin III and hypercoaguability has not been proven in the transplant setting. Some clinical and histologic data suggest that low plasma levels of these natural anticoagulant proteins promote thrombosis after hematopoietic cell transplantation. For example, patients with hepatic VOD often develop deposition of fibrin in the walls of terminal hepatic venules.⁸ In hematopoietic cell transplant patients, large vein thrombosis is an unusual complication⁹ and only sporadic cases of portal vein thrombosis,¹⁰ sinus vein thrombosis¹¹ and superior vena cava thrombosis¹² have been reported. Thrombosis at the site of venous access catheters is more common.^13,14 We now report eight patients who developed PVT after transplant, associated with VOD and decreased plasma levels of protein C and antithrombin III.

METHODS

Techniques of hematopoietic cell transplantation

The techniques of hematopoietic cell transplantation at the Fred Hutchinson Cancer Research Center have been described previously.¹⁵ Briefly, patients underwent a myeloablative conditioning regimen before infusion of either marrow or peripheral blood stem cells. The date of infusion is referred to as day 0. Patients receiving allografts were given immunosuppressive drugs to prevent GVHD, usually cyclosporine and methotrexate.¹⁶ Prophylaxis against viral infections (acyclovir) and fungal infections (fluconazole) was routine during 1994-1998.

Patient selection

Between March 1994 and January 1998, all patients who developed signs of liver dysfunction or right upper quadrant pain or ascites underwent abdominal Doppler ultrasound examination. PVT was diagnosed if echogenic material was observed in the portal vein and flow signals, as assessed by color Doppler ultrasound, were absent.^17,18 The frequency of PVT was defined by the number of patients with an ultrasound diagnosis of PVT divided by the total number of patients who underwent hematopoietic cell transplant during this time interval. Clinical and laboratory data at the time of diagnosis of PVT, treatment, outcome and cause of death were noted from medical records. This retrospective review was conducted under a protocol approved by the Institutional Review Board of the Fred Hutchinson Cancer Research Center.

Definition of VOD

The clinical criteria for VOD are: (1) hepatomegaly and/or liver tenderness, (2) weight gain of more than 2% of the baseline weight, and (3) an elevation of serum bilirubin level of more than 2 mg/dl. VOD was diagnosed if two or more these findings developed within 30 days of transplantation and there was no alternative explanation for these findings.^19,20,21

Laboratory methods

Blood specimens were collected over sodium citrate and centrifuged at 4°C. Assays for protein C and antithrombin III were performed at the Hemostasis Laboratory of the Puget Sound Blood Center, Seattle, WA, using a chromogenic method for antithrombin III (Iltest AT III; Instrumentation Laboratories, Lexington, MA, USA) and a functional assay for protein C (American Bioproducts Company, Parsippany, NJ, USA). The reference range for antithrombin III is 85-122%, and for protein C, 78-132%.

Results

Frequency of PVT

Of 1847 patients transplanted between March 1994 and January 1998, eight (0.4%) were diagnosed with PVT.

Patient characteristics before diagnosis of PVT (Table 1)

The median age was 48 (32-65) years. Five patients had received autologous and three allogeneic transplants following high-dose myeloablative therapy. The clinical conditions being treated by transplantation included leukemia (n = 4), myeloma (n = 2), and solid tumor (n = 2). Two patients had chronic hepatitis before transplant (hepatitis C in patient 3 and hepatitis B and C in patient 5), a risk factor for severe VOD of the liver; neither patient had clinical evidence of cirrhosis. Patient 1 had undergone laparotomy for small bowel obstruction and lysis of adhesions on day 27 post transplant, 9 days before the diagnosis of PVT. Patient 3 had undergone laparoscopic cholecystectomy for gallstones 1 month before transplant. All patients had engrafted, at a median of day 15 (range 9-28).

Patient characteristics on the day of PVT diagnosis (Table 1)

Diagnosis of PVT was made by Doppler ultrasound at a median of day 28 (range 3-58). All patients had clinical evidence of VOD of the liver on the day that PVT was diagnosed, with a median total serum bilirubin of 11.9 mg/dl (range 2.4-21.7 mg/dl) and a median weight gain from pre-conditioning baseline of 7.9% (range 2-24.6%). All patients had developed either hepatomegaly or liver pain. In patients 7 and 8, abdominal pain was related to liver tenderness even though hepatomegaly was not detected on physical examination. All patients had ascites proven by ultrasound on the day of diagnosis of PVT. There was no evidence of GVHD in any organ system at the time of diagnosis of PVT. Plasma levels of antithrombin III measured at the time of diagnosis of PVT in five patients were all below the normal range; the median value was 36% (range 22-66%). Plasma levels of protein C in six patients were also below the normal range; the median value was 20.5% (range 7-29%). In no patient was there clinical or radiological evidence of mesenteric ischemia.

Clinical course and outcome after diagnosis of PVT (Table 2)

Thrombolytic therapy with human recombinant tissue plasminogen activator (dose 20 mg/day, range 20-50, for 4 days, range 3-9) was given to six patients. This therapy was prescribed specifically for PVT in patients 3, 7 and 8, each of whom lacked clinical evidence of severe VOD at the time of diagnosis of PVT and who would not have been treated with thrombolysis otherwise. Patient 3, however, despite the disappearance of his PVT within 2 days after the start of thrombolytic therapy, deteriorated and died of VOD and multi-organ failure at day 47. Patients 7 and 8 resolved their PVT and recovered from VOD but died of recurrent myeloma and graft-versus-host disease, respectively. Thrombolytic therapy was given because of clinical evidence of severe VOD and not specifically for treatment of PVT in patients 1, 4 and 5. The PVT in patients 1 and 5 did not resolve and these patients died of VOD and multi-organ failure. Patient 4 had resolution of both PVT and VOD and is a long-term survivor. Thrombolytic therapy was not given to patients 2 and 6. Patient 2 had recent abdominal surgery as a contraindication to thrombolysis; his PVT resolved spontaneously but he died of VOD and multi-organ failure. Patient 6 had mild VOD that resolved. His PVT was noted to have resolved at an ultrasound examination at day 52, and he is a long-term survivor.

Discussion

In our study, of 1847 transplanted patients, eight patients (0.4%) were diagnosed with PVT, each of whom had clinical evidence of VOD. As VOD develops in 30-50% of patients who undergo myeloablative hematopoietic cell transplantation at our center,^19,20,22 we estimate the frequency of PVT among patients with VOD at 1%. An Australian group has previously reported three patients with PVT after autologous hematopoietic cell transplantation, with a denominator of 47 patients undergoing autologous hematopoietic cell transplantation.¹⁰ This study and our report were retrospective and may have underestimated the true incidence of PVT after transplantation. However, several prospective studies have examined the utility of ultrasound in the diagnosis of VOD after transplant: one of 229 observed patients without VOD and none of 75 patients with VOD was reported to have developed portal vein thrombosis during the period of observation,^{23,24,25,26,27} suggesting that the prevalence of PVT is not much higher than 1%. In our report, VOD was diagnosed before PVT was discovered or both VOD and PVT were diagnosed at the same time. The most likely explanation for the association between VOD and PVT is a diminished rate of flow in the portal vein caused by obstruction to sinusoidal blood flow, in turn caused by destruction of sinusoidal endothelial cells, sinusoidal constriction, and hepatocyte necrosis in zone 3 of the liver acinus.^28,29 Two patients had significant elevations of serum AST, a reflection of hepatocyte necrosis related to VOD and an uncommon finding in patients with PVT.¹

Results from measurement of protein C and antithrombin III at the time of diagnosis of PVT suggest that a hypercoagulable state may have contributed to the development of thrombus. That is, plasma levels of protein C were in a range associated with thrombus formation in other clinical settings where protein C levels are low.³⁰ Furthermore, protein C levels in plasma in this series were lower than levels reported from prospective series of patients undergoing hematopoietic cell transplantation.^5,6,7 Antithrombin III levels in five patients were also below normal, but not as abnormal as protein C values. The cause of low levels of protein C and antithrombin III in transplant patients is not known with certainty, but there is a strong association with VOD.³¹ One possibility is that these natural anticoagulants are lost into the ever-expanding extravascular fluid compartment that is characteristic of patients with progressive VOD, a hypothesis supported by the correlation between falling plasma antithrombin III levels and the amount of extravascular fluid accumulation during steady-state infusion of antithrombin III.³² We did not measure factor V Leiden in this series but in other series of patients undergoing hematopoietic cell transplantation, no patients with factor V Leiden were found among patients with or without VOD.^33,34

The clinical course of these patients, including response to treatment with a thrombolytic agent, suggests that PVT is a marker for the severity of VOD and not a cause of morbidity per se. We could not identify a clinical syndrome that would allow identification of PVT, that is, patients with VOD and PVT had clinical presentations and courses that were indistinguishable from patients with VOD without PVT. It is not clear whether thrombolytic therapy altered the natural history of PVT in this cohort, as PVT resolved in 4/6 patients who received thrombolytic therapy and 2/2 patients who did not. Given the morbidity associated with the use of thrombolytic therapy in thrombocytopenic transplant patients such as these,³⁵ we suggest that thrombolytic therapy be used cautiously as a treatment for PVT, particularly in patients with mild VOD.³⁶ The primary indication for thrombolytic therapy would be development of mesenteric vascular ischemia. Use of low molecular weight heparin is probably a safer therapeutic alternative that may be effective,¹⁰ but there is a risk of variceal hemorrhage in patients with PVT that must also be considered.¹

In conclusion, PVT developed in eight of 1847 patients who underwent hematopoietic cell transplantation at our institution and was associated with hepatic VOD and low plasma levels of protein C and antithrombin III. We speculate that low levels of these natural anticoagulants contribute to the development of PVT in patients with VOD and diminished portal venous flow rates. Four patients with PVT died of severe VOD and multi-organ failure, but PVT did not appear to contribute to these deaths.

Acknowledgements

Our research was supported by the following grants from the National Institutes of Health, National Cancer Institute: CA 18029 and CA 15704.

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Table 1 Clinical and laboratory features of 8 patients with portal vein thrombosis

Table 2 Clinical course and outcome of eight patients with portal vein thrombosis