Case 8 -

Chronic Rejection Julia C. Iezzoni

Clinical History The patient, a 24-year-old Caucasian male, underwent and emergency orthotopic liver transplantation for fulminant hepatic failure due to a Tylenol overdose taken as a suicide attempt. Four weeks after transplantation, he developed moderate acute cellular rejection, which only partially responded to immunosuppressive therapy. Over the next five months, the patient's aminotransferases remained mildly elevated, but his alkaline phosphatase and total bilirubin continued to rise. A liver biopsy was performed. Diagnosis: Chronic Rejection Case 8 - Figure 1 - H&E Case 8 - Figure 2 - H&E Pathologic findings: Sections of the liver allograft biopsy show small, fibrotic portal tracts devoid of bile ducts. There is little or no remaining portal inflammation, and the portal tracts have a "burnt out" appearance. In addition, in the centrilobular regions there is perivenular sclerosis. Discussion Definition and terminology Chronic hepatic allograft rejection is a distinct clinicopathologic type of rejection that is characterized by the progressive loss of interlobular and septal bile ducts, obliterative arteriopathy, and unrelenting cholestasis. Typically, chronic rejection is irreversible and is associated with a high incidence of allograft dysfunction and failure, necessitating re-transplantation. Because of this outcome, chronic rejection is a significant cause of late allograft failure. Unfortunately, chronic rejection remains a diagnostic problem due to its often times insidious development, as well as the uneven distribution within the liver of the characteristic histologic features. Due to both the variability of the histologic features as well as the time frame for disease onset, the terminology used to designate this form of hepatic allograft rejection is confusing. Specifically, while the cardinal histologic findings of intrahepatic bile duct loss and obliterative arteriopathy are both present in most cases, a significant minority of cases demonstrate just one of these two histologic features. Terms such as "vanishing bile duct syndrome" or "ductopenic rejection" have been used for cases with only the bile duct loss, whereas "chronic vascular rejection" has been applied to cases with just the vascular findings. Variably combinations of intrahepatic bile duct loss and/or obliterative arteriopathy, however, now are accepted as the morphologic definition of chronic rejection. In addition, criticism of the use of term "chronic" has been made since the characteristic histologic changes can manifest as early as 20 days after transplantation. Although the term "chronic" traditionally implies an advanced timeframe, none is intended in this context. Though imperfect, "chronic rejection" is currently the accepted term for this form of hepatic allograft rejection. Clinical features The incidence of chronic rejection has declined over the last two decades. In the 1980's, the incidence of chronic rejection at 5 years post-transplantation was 15% to 20%. Currently, most centers report rates of 3% to 5%. This decrease is probably in part due to better control of episodes of acute cellular rejection (ACR) and improved recognition of chronic rejection early in its course, when it is potentially treatable. The incidence in children, however, remains high, with rates ranging from 8% to 20%. A variety of risk factors for the development of chronic rejection have been identified. The single greatest risk for chronic rejection is re-transplantation for allograft failure due to chronic rejection. For example, one study reported an overall incidence of chronic rejection of 4%; in those patients undergoing re-transplantation for allograft failure due to chronic rejection, however, the incidence rose to 17% for development of chronic rejection in the second allograft. Autoimmune liver disease (i.e. autoimmune hepatitis, primary biliary cirrhosis, primary sclerosing cholangitis) as the underlying original liver pathology is associated with an increased incidence of chronic rejection compared with non-autoimmune causes. Recipient age, especially younger than 1-year-old, is a significant risk for developing chronic rejection. This may be related to an overall decrease in the immune response associated with increasing age. Other factors include CMV infection, insufficient immunosuppression, a variety of donor-recipient mismatch factors, and the use interferon therapy, which may be administered for treatment of recurrent or de novo hepatitis C infection. In addition, since chronic rejection usually follows recurrent or persistent ACR, the histologic severity and number of episodes of ACR is associated with the relative risk for development of chronic rejection. The onset of chronic rejection is variable. Most cases present 2 to 12 months after transplantation. Documented cases of chronic rejection, however, have occurred within the first month post-transplantation, whereas other cases have presented more than a year after surgery. Accordingly, chronic rejection may be diagnosed essentially at any time in the post-transplantation period. The majority of cases of chronic rejection arise in the background of ACR that is unresponsive to immunosuppressive therapy. In this setting, the chronic rejection develops after one or more episodes of ACR that ultimately fail(s) to respond to maximal immunosuppressive therapy. While the initial liver biopsy demonstrates the typical features of ACR, follow-up biopsies show persistent immune-mediated bile duct injury. As the rejection process evolves, subsequent biopsies demonstrate progressive injury with the characteristic histologic features of chronic rejection, as will be discussed below. Less commonly, chronic rejection can develop insidiously without a history of previously recognized episodes of ACR. In either case, ultimately the patient develops allograft failure. Chronic rejection is characterized clinically by progressive jaundice and a relentless increase in markers of cholestasis, including alkaline phosphatase, gamma-glutamyltranspeptidase, and bilirubin. Despite anti-rejection therapy, these biochemistries remain elevated, which reflects the continued bile duct damage. With progressive damage, evidence of impaired synthetic function manifests eventually, with subsequent allograft failure in most cases. While characteristic, this pattern of liver biochemistries is not specific for chronic rejection and cannot distinguish between chronic rejections and other insults to the hepatic allograft. Initially, chronic rejection was regarded as a universally progressive, irreversible condition that was unresponsive to additional immunosuppressive therapy and lead to inevitable allograft loss. Subsequently, several reports documented partial or complete clinical, biochemical, and histological recovery in patients who otherwise had typical features of chronic rejection. This resolution was gradual, typically occurring over a period of 4 to 6 months, but in several patients, this recovery took over a year after the diagnosis of chronic rejection. As such, it is now clear that the diagnosis of chronic rejection is not synonymous with irreversible allograft loss in all cases. Importantly, recent studies have suggested that chronic rejection that is diagnosed early in its course can be reversed, and the hepatic allograft can be salvaged using new immunosuppressive agents. Key to this important advancement is the ability to diagnosis chronic rejection at an early stage, which allows for interventional therapy before irreversible injury has occurred. Pathogenetic mechanism While the pathogenetic mechanisms are not understood in full, the hepatic allograft injury in chronic rejection is due to the cumulative and progressive effect of both immune-mediated damage and ischemic damage. In most cases, chronic rejection is preceded by one or more episodes of ACR. The density of the portal inflammatory infiltrates diminishes as a result of the progressive disappearance of the bile ducts, which are the main target antigens. As such, the bile duct damage in chronic rejection appears to be in part an alloimmune T cell-mediated injury, similar to ACR. In addition, there is obliterative arteriopathy of the second and third order branches of the hepatic artery. The mechanism for the arteriopathy is poorly understood, but it is likely mediated by interactions of inflammatory cells, endothelial cells, myofibroblasts, cytokines, with possible induction of atherosclerotic-type changes. Since the sole blood supply to bile ducts is derived from hepatic artery branches, the obliterative arteriopathy results in ischemic damage to the bile ducts. Accordingly, the bile duct loss in chronic rejection results from both alloimmune-mediated injury as well as ischemic damage. In addition, since acinar zone 3 is the hepatic lobular area that is most susceptible to ischemia, the obliterative arteriopathy also results in centrilobular ischemic injury. Pathology Several general principles are applicable to liver biopsy interpretation for possible chronic rejection: Definitive diagnosis is of chronic rejection is not made on histology alone. The diagnosis of chronic rejection is based on the combination of clinical/radiological/laboratory and histologic findings. Not all of the portal tracts are affected simultaneously. While some demonstrate bile duct loss, other may be normal, and others yet may show ACR. As such, the liver biopsy for chronic rejection is highly subject to sampling effect. Pathogenetically, clinically, and histologically there appears to be a continuum between intractable ACR and chronic rejection. As such, identification of an exact histologic "cut off point" between persistent ACR and early chronic reject often is difficult. Since chronic rejection is characterized by progressive injury, repeat biopsies demonstrating sequential damage often are needed to make a definitive diagnosis. This is especially true for biopsies early in the course of chronic rejection, as the early histologic changes are particularly difficult to interpret. The histologic hallmarks of chronic rejections are: Bile duct loss Obliterative arteriopathy and Secondary parenchymal changes. Bile duct loss: Chronic rejection causes progressive damage and then loss of the interlobular bile ducts. Early in its course, there is a scant portal inflammatory infiltrate. This infiltrate is composed of lymphocytes and is devoid of the neutrophils or eosinophils seen in ACR. Morphologically, the early bile duct injury manifests as eosinophilic transformation of the biliary epithelial cytoplasm, uneven nuclear spacing, syncytia formation, nuclear enlargement and hyperchromasia, and ducts only partially lined by epithelium. Subsequent biopsies show a progressive loss of interlobular ducts. Following ductal destruction, the portal inflammatory infiltrate dissipates, presumably due to the disappearance of the target antigens. End-stage portal tracts are small, slightly fibrotic, devoid of inflammation, with a "burnt out" appearance. As such, they are inconspicuous and easily overlooked. A trichrome stain accentuates the absence of the bile duct. Estimation of bile duct loss is achieved by calculating the ratio of portal tracts without identifiable ducts to the total number of portal tracts present. Twenty portal tracts are considered the minimum number necessary to evaluate for possible bile duct loss. Sequential biopsies over a period of months often are needed to reach this required number of portal tracts. Obliterative arteriopathy: Obliterative arteriopathy usually is not observed in needle core biopsy specimens, because this process mainly affects the medium and large arteries in the hilum, perihilar region, and larger portal zones. When available for evaluation, these vessels demonstrate narrowing due to an intimal and subinitmal deposition of lipid-laden macrophages ("foam cells"), which are recipient-derived. Over time, this foam cell infiltrate can be accompanied by a proliferation of subintimal myofibroblasts. The resultant narrowing varies from partial to complete arterial occlusion. Smaller interlobular arterioles and portal and hepatic veins may be involved as well but typically to a lesser extent. Portal arterioles may disappear in long-standing cases. Secondary parenchymal changes: Ischemic injury of the hepatic parenchyma due to the obliterative arteriopathy typically is detected in liver core biopsy specimens with chronic rejection. This injury is most prominent in the centrilobular region, since this is the area within the hepatic acinus that is most susceptible to ischemia. Early injury manifests as perivenular hepatocyte drop out with mild perivenular fibrosis. This may be accompanied by an inflammatory infiltrate. Over time this injury progresses to widespread centrilobular hepatocyte loss with bridging fibrosis and occasional obliteration of terminal hepatic venules. Centrilobular hepatocyte ballooning, hepatocanalicular cholestasis, and sinusoidal Kupffer cells aggregates also may be evident. In a biopsy specimen, the minimal diagnostic criteria for chronic rejection are: 1) the presence of bile duct atrophy/pyknosis, affecting a majority of the bile ducts, with or without bile duct loss; 2) convincing foam cell obliterative arteriopathy; or 3) bile duct loss affecting greater than 50% of the portal tracts. Banff staging of chronic rejection As mentioned above, reports suggest that chronic rejection can be successfully treated (i.e. reversed) if intervention is performed early in its course. Accordingly, a staging system for chronic rejection has been proposed that provides information about the relative structural integrity of the allograft (Table 1). This information can be used to help guide patient management. Of note, this staging system presupposes that the diagnosis of chronic rejection has been established, and that the staging system should not to be used to determine whether the histologic features in a given case are due to chronic rejection or some other condition. Importantly, this histologic staging provides only rough, working guidelines. The decision to increase immunosuppression or re-transplant is based on the clinical and laboratory data in conjunction with the histologic features. Table 1: Banff staging: Features of early and late chronic rejection Structure Early chronic rejection Late chronic rejection Small bile ducts (<60 m) Degenerative changes involving a majority of ducts; eosinophilic transformation of the cytoplasm; increased N:C ratio; nuclear hyperchromasia; uneven nuclear spacing; ducts only partially lined by biliary epithelial cells Bile duct loss in <50% of portal tracts Degenerative changes in remaining bile ducts Loss in 50% of portal tracts Terminal hepatic venules and zone 3 hepatocytes Intimal/lumenal inflammation Lytic zone 3 necrosis and inflammation Mild perivenular fibrosis Focal obliteration Variable inflammation Severe (bridging) fibrosis Portal tract hepatic arterioles Occasional loss involving <25% of portal tracts Loss involving >25% of portal tracts Other So-called "transition" hepatitis with spotty necrosis of hepatocytes Sinusoidal foam cell accumulation; marked cholestasis Large perihilar hepatic artery branches Intimal inflammation, focal foam cell deposition without lumenal compromise Lumenal narrowing by subintimal foam cells Fibrointimal proliferation Large perihilar bile ducts Inflammation damage and foam cell deposition Mural fibrosis Differential diagnosis A similar pattern of duct injury and bile duct loss can be a result of non-rejection-related complications, such as obstructive cholangiopathy (which in not always associated with bile ductular proliferation), hepatic artery thrombosis, adverse drug reactions, and CMV infections. Differentiation of these possibilities from chronic rejection typically requires correlation with thorough clinical, laboratory, and radiographic studies. References An International Panel. Update of the international Banff schema for liver allograft rejection: working recommendations for the histopathologic staging and reporting of chronic rejection. Hepatol 2000;31792-799. Hubsher SG, Buckels JAC, Elias E, McMaster P, Neuberger J. Vanishing bile duct syndrome following liver transplantation – is it reversible? Transplantation 1991;51:1004-1010. Neil DAH, Hubscher SG. Histologic and biochemical changes during evolution of chronic rejection of liver allografts. Hepatol 2002;35:639-651. Wiesner RH, Batts KP, Krom RAF. Evolving concepts in the diagnosis, pathogenesis, and treatment of chronic hepatic allograft rejection. Liver Transpl Surg 1999:388-400.