Hepatitis C Virus-Associated Renal Diseases
- The presence of circulating hepatitis C viral RNA and antibody.
- Type I membranoproliferative glomerulonephritis.
- Circulating type II mixed cryoglobulins [polyclonal immunoglobulin (Ig)G and monoclonal IgMκ rheumatoid factor].
- Strong association with hepatitis C virus (HCV) infection chronicity.
- Very low serum C4, C1q, and CH50, but normal C3 levels.
The clinical manifestations associated with “mixed” cryoglobulinemia were first described in 1966. They included a constellation of clinical features that consisted of the triad of palpable purpura, arthralgias, and weakness plus variable degrees of glomerulonephritis, lymphadenopathy, and hepatosplenomegaly in some patients. Cryoglobulinemia in these patients had a “mixed” composition of IgG and IgM rheumatoid factor (RF). The cause of this disease was unknown in those days, and its association with hepatitis C virus (HCV) infection became increasingly apparent only after its discovery in 1989. It is now apparent that the classic clinical triad occurs in a minority of patients and that the main characteristic of the disease is the markedly heterogeneous manifestations of a systemic vasculitis, with purpuric skin lesions that show leukocytoclastic vasculitis on biopsy being an almost constant and predominant feature.
Hepatitis C Virus Virology
HCV is a small RNA virus that is included in the Flaviviridae family and has recently been classified as the sole member of the genus Hepacivirus. HCV is a small double-shelled virus consisting of a lipid envelope (E) with virally encoded glycoproteins (E1 and E2) and an inner nucleocapsid (core) that contains a positive-sense single-stranded RNA genome of 9500 nucleotides. It has well-defined structural (core, E1, and E2) as well as several nonstructural (from NS2 to NS5) proteins. The nonstructural proteins encode several proteases, a virus-specific helicase, and an RNA-dependent RNA polymerase responsible for replication of the genome. The evolution of HCV has been characterized by the emergence of six major genotypes based on sequence homology, and more than 50 subtypes.
To date, around 170–200 million individuals worldwide are estimated by the World Health Organization to have chronic HCV infection. Although HCV infection appears to be primarily a disease that is almost exclusively confined to the liver, a wide variety of extrahepatic disease manifestations have been reported to be associated with HCV infection. The prevalence of extrahepatic diseases is not known with certainty, but it suggests that HCV is involved in nonhepatic pathologic processes.
Two immunologic features of HCV may predispose patients to manifestations of extrahepatic disease. First, HCV is known to evade immune elimination and lead to chronic infection and accumulation of circulating immune complexes. Membranoproliferative glomerulonephritis (MPGN) associated with HCV infection may be the result of this phenomenon. The second feature is that HCV stimulates production of monoclonal rheumatoid factors (mRF). This feature causes type II cryoglobulinemia that is responsible for most of the symptomatic cryoglobulinemic vasculitis. Although this manifestation occurs relatively infrequently, as do all the extrahepatic disease manifestations, it is an important extrahepatic involvement of chronic HCV infection responsible for much of the increased morbidity and mortality accompanying the disease.
The prevalence of mixed cryoglobulinemia increases with the duration of the hepatitis. Patients with chronic hepatitis C who have mixed cryoglobulinemia have an apparent duration of disease that is almost twice as long as those without cryoglobulinemia. A high prevalence of mixed cryoglobulinemia (35–90%) has been reported for patients with HCV infection. However, the prevalence of mixed cryoglobulinemia has not been assessed in populations of unselected HCV-infected patients. Hence, reports of high prevalence of mixed cryoglobulinemia may be influenced by selection bias, eg, studies on cirrhotic patients with long-standing HCV infection from gastroenterology centers. Frank symptomatic cryoglobulinemia occurs in 1% or less of patients and is usually associated with high levels of RF and cryoglobulins. Testing unselected patients with cryoglobulinemia has shown that up to 90% have anti-HCV antibody. Type I MPGN has long been regarded as idiopathic, but a considerable proportion of patients has concomitant chronic infection with HCV. The exact proportion of patients with type I MPGN who are anti-HCV-antibody positive is unknown.
The most frequent form of renal involvement in HCV infection is MPGN, described mainly in the United States and Japan. The real prevalence of MPGN without detectable cryoglobulinemia is difficult to assess. Such cases might represent a subclinical form of cryoglobulinemia because of failure to detect circulating cryoglobulins by standard laboratory techniques or inadequate methods. In addition, the production of IgM antibodies with anti-IgG activity might induce immune complexes without cryoprecipitable properties. Finally, these patients may develop detectable circulating cryoglobulinemia only later in the course of the disease.
Cryoglobulinemia is defined as the presence in serum of immunoglobulins that precipitate at reduced temperatures (Figure 35–4). Therefore, blood samples obtained from patients for detection of cryoglobulins must be stored and transported at 37°C.
A: Whitish cryoprecipitates forming in Wintrobe's tube after standing at 4°C for 72 hours followed by centrifugation at 400 × g for 10 minutes. The cryocrit is approximately 30%. B: Immunofixation of the washed, dissolved cryoprecipitate typed a monoclonal IgMκ with polyclonal IgG. By definition, these are type II cryoglobulins. (Courtesy of Dr Janette S.Y. Kwok, Department of Pathology, Queen Mary Hospital, Hong Kong, China.)
Cryoglobulins were classified based on their Ig composition, and three types were defined. Type I consists of a single monoclonal Ig without antibody activity, and can be found in patients with multiple myeloma, Waldenström's macroglobulinemia, or idiopathic monoclonal gammopathy. Types II and III, or mixed cryoglobulins, consist of polyclonal IgG and monoclonal IgMκ (type II) or polyclonal IgM (type III) with RF activity (Table 35–1). When no definite disease association is found, the condition is referred to as essential mixed cryoglobulinemia. The observation that up to 90% of unselected patients with cryoglobulinemia have anti-HCV antibody indicates that the disease is not genuinely “essential,” but more likely is related to HCV infection. Hence, the term “essential” may be a misnomer and can no longer be used for the majority of cases, where cryoglobulins consist of complexes of RF, IgG, anti-HCV antibody, and HCV virions. The pathogenesis of cryoglobulinemia due to HCV infection is not well understood, but it appears to be related to excessive proliferation of B cells as a result of the chronic antigenic stimulation of HCV infection.
Table 35–1. Classification of Cryoglobulins. ||Download (.pdf)
Table 35–1. Classification of Cryoglobulins.
Most common disease association
Other disease associations
Single monoclonal IgG, IgA, or IgM
Waldenström's macroglobulinemia Idiopathic monoclonal gammopathy
Chronic lymphocytic leukemia
Polyclonal IgG and monoclonal IgM
Chronic lymphocytic leukemia
Polyclonal IgG and polyclonal IgM
Connective tissue disease, particularly RA
Chronic liver disease
Hepatitis C Virus-Related Cryoglobulinemia
Full-blown symptomatic cryoglobulinemia occurs infrequently, and the typical symptoms are fatigue and palpable purpura, which histologically consists of a leukocytoclastic vasculitis (with complexes of anti-HCV antibody and HCV in injured tissue). These lesions are usually found on the lower limbs (Figure 35–5), although they can occur anywhere, and represent small vessel vasculitis. A smaller proportion of patients has fever, arthritis, Raynaud's phenomenon, and neuropathy. Peripheral neuropathy is usually characterized by paresthesias and variable degrees of motor deficits. Abdominal pain arises from mesenteric vasculitis, and may mimic an acute abdomen during disease flare. Hepatosplenomegaly is due to chronic liver disease as a result of HCV. Cryoglobulinemia is more common in women than men and typically occurs after a prolonged period, often years or decades, of HCV infection. Although the course of illness tends to wax and wane, occasionally the systemic illness can be severe or even fulminant. For instance, nodular pulmonary infiltrates from deposition of cryoglobulins leading to respiratory failure (Figure 35–6) and non-Hodgkin's B cell and splenic lymphomas have been reported to arise in the setting of cryoglobulinemia. In addition, cryoglobulinemia has also been anecdotally reported in association with adenocarcinoma of the liver and stomach in Chinese.
Palpable purpuric skin lesions in the lower limbs of a patient with cryoglobulinemia. Such lesions are characteristic of any causes of small vessel vasculitis, but not pathognomonic of the rashes in cryoglobulinemia. (Courtesy of Dr. Chi-keung Yeung, Department of Medicine, Queen Mary Hospital, Hong Kong, China.)
Nodular pulmonary infiltrates in a patient with cryoglobulinemia. Note also a right internal jugular venous catheter in situ for plasmapheresis and hemodialysis.
The principal renal manifestation of HCV infection is MPGN type I, usually in the context of cryoglobulinemia. Type II MPGN (eg, dense deposit disease) has not been described in association with HCV infection. From studies in Italy, the United States, and Japan, MPGN associated with type II cryoglobulinemia is the predominant type of glomerulonephritis clinically associated with HCV infection. The prevalence of MPGN in HCV type II cryoglobulinemia is approximately 30%. On the other hand, the prevalence of anti-HCV antibody among patients with MPGN is much lower in Chinese people. MPGN is also occasionally observed in patients with hepatitis C in the absence of cryoglobulinemia.
Renal disease is rare in children and the typical age of disease onset is in the fifth or sixth decade of life after long-standing infection, often in association with mild subclinical liver disease. Clinically, patients may have other symptoms of cryoglobulinemia, such as palpable purpura and arthralgias. Renal manifestations include nephrotic (20%) or nonnephrotic proteinuria and microscopic hematuria. Acute nephritic syndrome is the presenting feature in about 25% of cases. Progression to uremia is associated with male gender and old age. Renal insufficiency, frequently mild, occurs in about 50% of patients. Over 80% of patients have refractory hypertension upon presentation, which may be responsible for a considerable number of cardiovascular deaths.
The natural history of HCV-related cryoglobulinemia remains poorly defined. The clinical course can vary dramatically. The renal disease tends to have an indolent course and does not progress to uremia despite the persistence of urine abnormalities in the majority of patients. Around 15% of patients eventually require dialysis according to an Italian series.
Laboratory testing coupled with renal biopsy establishes the diagnosis of HCV-related MPGN. Most patients will have anti-HCV antibody, as well as HCV RNA, in serum. Serum transaminase levels are elevated in 70% of patients. Cryoglobulins are detected in 50–70% of patients. Serum electrophoresis and immunofixation reveal type II mixed cryoglobulins (Figure 35–4B), in which the monoclonal rheumatoid factor, almost invariably an IgMκ, is a distinguishing feature of cryoglobulinemic glomerulonephritis. Their amount, usually measured as a cryocrit, varies from one patient to another, and varies from time to time in a given patient (ranging between 2% and 70%). Urine κ light chains are also commonly present. The serum complement pattern, which does not change much with clinical activity, is also discriminative. Characteristically, the early complement components (C4 and C1q) and CH50 are at very low, or even undetectable, levels, while the C3 level tends to remain normal or only slightly depressed.
Renal histologic evaluation typically shows evidence of immune complex deposition in glomeruli and changes of MPGN. MPGN refers to a pattern of glomerular injury characterized by diffuse mesangial proliferation and thickening of the capillary wall, hence the synonym of mesangiocapillary glomerulonephritis (Table 35–2). In cryoglobulinemic MPGN, light microscopy reveals an increased number of mesangial cells, expansion of the mesangial matrix, and diffuse accentuation of glomerular tufts, which gives a lobular appearance to the glomeruli (Figure 35–7A). Glomerular capillary walls appear thickened because of the interposition of the mesangial matrix between the glomerular basement membrane (GBM) and the endothelium. Staining of the GBM with periodic acid–Schiff or silver stain shows splitting (“double contour”) or “tram-tracking” due to insertion of the mesangial matrix (Figure 35–7B). Immunofluorescence reveals granular deposits of C3 and IgG in the mesangium and in peripheral capillary loops (Figure 35–7C). A similar morphologic appearance may be seen with infective endocarditis and infected ventriculoatrial shunts (shunt nephritis). In addition, glomerular capillaries may have marked inflammatory cell infiltrates with both mononuclear cells and polymorphonuclear leukocytes (Figure 35–7A), a distinguishing feature from noncryoglobulinemic MPGN. Intracapillary globular accumulations of eosinophilic material representing precipitated immune complexes or cryoglobulins may also be present. Viral HCV-containing antigens had previously been detected in glomerular structures using a three-stage indirect immunohistochemical monoclonal antibody technique but this has not been confirmed by subsequent studies. Electron microscopy shows subendothelial deposits (Figure 35–7D) that may have a tactoid pattern, size, and distribution (Figure 35–7E), suggestive of cryoglobulin deposition. These tend to be of 15–30 μm in size, distinguishing them from the smaller fibrillary deposits (12–25 μm). The presence of immunotactoid glomerulonephritis in a viral disease confirms the association of immunotactoid glomerulonephritis with a systemic disorder, while fibrillary glomerulonephritis is more frequently a “primary” condition. Fibrillogenesis may be favored by circulating paraproteins interacting with matrix proteins in the glomerulus, such as fibronectin. The animal model of membranoproliferative glomerulonephritis derived from induction of mixed cryoglobulinemia strongly suggests a pathogenetic role of cryoglobulins rather than a direct etiologic role of HCV infection. Of interest, however, and again in animal models, both rheumatoid factor and cryoglobulinemic properties may be necessary for the development of skin vasculitis, but cryoglobulin activity alone is sufficient to induce glomerular lesions.
Table 35–2. Comparison of Glomerulonephritis Related to Chronic Hepatitis Virus Infection. ||Download (.pdf)
Table 35–2. Comparison of Glomerulonephritis Related to Chronic Hepatitis Virus Infection.
HBV Membranous/mesangiocapillary GN
HCV mesangiocapillary GN
Route of infection
Vertical or horizontal in children, intravenous or sexual in adult
Children and adult
Adult (fifth and sixth decade)
History of liver disease
Absent in endemic areas
Abnormal liver function
Microscopic hematuria/proteinuria, nephrotic syndrome <20%
Occasional, 29% in 5 years
15% in 10 years
10-year probability of survival without dialysis
49% mainly due to extrarenal complications
40%—CVA, hematologic malignancy, infection, liver failure
Pathology of membranoproliferative glomerulonephritis type I associated with cryoglobulinemia. A: Glomerulus exhibits a diffuse increase in mesangial cellularity and matrix with accentuation of lobulation of tuft architecture, obliteration of capillary lumens, and leukocytic infiltrate (×200, H&E). B: Periodic acid–Schiff and methenamine silver staining reveal prominent double contours or tram-tracking (arrows) of the glomerular basement membrane (×400). C: Immunofluorescence reveals granular deposits of C3 (shown here) and IgG in the mesangium and in peripheral capillary loops (×200). D: Electron microscopy shows markedly increased glomerular cellularity and subendothelial deposits (arrowheads), indicative of cryoglobulin deposition. The thickened glomerular basement also incorporates cell processes (arrow), indicative of mesangial interpositioning (×10,500). E: Several tactoids are also seen. These are highly electron-dense deposits (arrows) that are most likely crystalline immune complexes as they are surrounded by accompanying nonstructured, less electron-dense materials (arrowhead) (×7800). (Courtesy of Dr. Kwok-wah Chan, Department of Pathology, Queen Mary Hospital, Hong Kong, China.)
Other forms of glomerular injury have been associated with HCV infection in individual case reports and small series, including membranous glomerulonephritis, IgA nephropathy, focal and segmental glomerulosclerosis, fibrillary glomerulonephritis, immunotactoid glomerulopathy, rapidly progressive glomerulonephritis, exudative–proliferative glomerulonephritis, and lupus nephritis. Membranous nephropathy in HCV carriers is characterized by the absence of cryoglobulins and male predominance.
In general, therapy can be directed at two levels: (1) Removal of cryoglobulins by plasmapheresis and (2) inhibition of their synthesis through either attenuation of the immune responses (using corticosteroid or cytotoxic agents) or suppression of viral replication (using interferon and ribavirin).
Before the association between HCV and cryoglobulinemic MPGN was unraveled, corticosteroid and cyclophosphamide were the mainstay of treatment. High-dose pulse methylprednisolone (1 g/day for 3 consecutive days), followed by oral steroids, was used to control the systemic illness. Plasmapheresis may be applied to remove circulating cryoglobulins, thus preventing their deposition in glomeruli and blood vessel walls. Cyclophosphamide ameliorates the vasculitic injury and inhibits the production of monoclonal rheumatoid factors by B-lymphocytes.
Our current understanding of the association between mixed cryoglobulinemia and HCV infection has resulted in a more rational approach to the treatment of this condition. Controlled trials have shown that antiviral therapy with interferon-α is associated with improvements in systemic symptoms of immune complex disease. However, relapse after therapy occurs in a large proportion of patients, particularly with interferon monotherapy given for short durations. Combination therapy with interferon-α2b plus ribavirin represented an important milestone in the treatment of chronic hepatitis C and acute hepatitis C after renal transplantation. Such cocktail therapy has also produced favorable results in mixed cryoglobulinemia, although nonresponses and relapses after initial improvements still occur. In some instances in which sustained viral eradication was unsuccessful, long-term maintenance interferon therapy has led to amelioration of disease. The introduction of pegylated forms of interferon (peginterferon) in 2000 represented another breakthrough in the treatment of chronic hepatitis C. Pegylation refers to the covalent attachment of a large inert molecule of polyethylene glycol (PEG) to a protein to yield a molecule that retains biological activity, but has delayed absorption and clearance, allowing for weekly rather than daily or three times a week administration. Delayed clearance also led to greater, more potent, and longer lasting antiviral effects. Recent data on peginterferon and ribavirin combination therapy in treating HCV infection are encouraging. Furthermore, the higher treatment failure rate of HCV carriers with genotype 1 is recognized.
Despite reports that antiviral therapy can occasionally be associated with the worsening of renal disease or a variable response, there are increasing observational studies suggesting the effectiveness of peginterferon and ribavirin combination therapy in treating HCV-associated cryoglobulinemic membranoproliferative glomerulonephritis. One therapeutic drawback lies in the hemolytic effect that complicates ribavirin therapy, particularly in patients with functional renal impairment. This therapeutic difficulty has been overcome by adjusting the dose according to the glomerular filtration rate instead of body weight alone and utilizing recombinant erythropoietin to overcome anemia. It is necessary to follow ribavirin serum levels when using this approach. Posttreatment renal biopsy showed histologic improvement in two of the three patients who received combination therapy for 12 months. In another study in which the viral genotypes were documented, genotype 1 was again associated with a lower sustained virologic response rate even with combined interferon-α and ribavirin therapy. In severe acute flares of cryoglobulinemia with glomerulonephritis or vasculitis, an appropriate approach is to include corticosteroids and cyclophosphamide as needed to control severe cryoglobulinemic symptoms in addition to combination antiviral therapy. In the most severe cases, plasmapheresis (three to four times weekly exchanges of 3 L of plasma for 2–3 weeks) can be helpful. For refractory cases, monoclonal antibody against the B cell surface antigen CD20 (Rituximab) has been reported to be efficacious with a favorable side-effect profile.
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Hepatitis B Virus-Associated Renal Diseases
- Membranous nephropathy is the most frequent association.
- The presence of circulating hepatitis B virus (HBV) or DNA.
- The presence of HBV-specific antigen(s) or viral genome in the glomerulus.
- Serum C3 and C4 levels may be low in 20–50%.
Following the landmark discovery in 1965 of the Australian antigen, subsequently renamed the hepatitis B surface antigen (HBsAg), the occurrence of membranous nephropathy (MN) due to glomerular deposition of Australian antigen-containing immune complexes was described in a 53-year-old man in 1971. Different histologic types of glomerular lesions have since been described in association with HBV carriage; however, the most striking is still MN.
Hepatitis B Virus Virology
HBV is a hepatotropic, double-stranded DNA virus belonging to the family Hepadnaviridae. HBV has a double-shelled virion 42–47 nm in diameter, a 27-nm internal core, an excess of incomplete 22-nm spheres, and a circular DNA, with a length varying between 3000 and 3300 base pairs. The DNA genome contains only four genes that encode viral proteins. These include the surface (S) gene, which encodes the three forms of HBsAg, the precore/core (PC/C) gene, which encodes the core protein and hepatitis B e antigen (HBeAg), the X gene, which encodes the X protein, and the polymerase (P) gene, which encodes the viral DNA polymerase. HBV is itself not cytopathic; hepatitis develops as a result of the host's immune reaction toward infected hepatocytes. HBV utilizes a replication strategy closely related to retroviruses, in that transcription of RNA into DNA is a critical step. Unlike retroviruses, HBV DNA is not integrated into host cell DNA during replication. After an HBV particle binds to and enters a hepatocyte, HBV DNA enters the cell nucleus and is converted into covalently closed circular DNA (cccDNA), which is highly stable acting as the intermediate template for transcription of RNA copies. This pregenomic mRNA is transported to the cytoplasm and has the dual functions of acting as a template for synthesis of new HBV DNA and carrying genetic information to direct the synthesis of viral proteins.
An estimated 350–400 million people worldwide are now infected with HBV. The reported prevalence of HBV-associated nephropathy, particularly MN, closely parallels the geographic patterns of prevalence of HBV. HBV infection occurs throughout the world and is endemic in developing countries, such as Africa, Eastern Europe, the Middle East, Central Asia, China, Southeast Asia, the Pacific Islands, and the Amazon basin of South America (with prevalence rates up to 10% or higher).
In endemic areas, transmission is usually vertical from infected mother to child. Horizontal transmission occurs via direct contact with blood (as in blood transfusions) or mucous membranes (as in sexual contacts), or via the percutaneous route upon contact with blood or body fluids (as in illicit intravenous drug use and needle-sharing practices).
The only definitive means to prove that a particular glomerulopathy is etiologically associated with HBV infection is to fulfill the following criteria:
The presence of circulating HBV antigen or DNA and HBV-specific antigen(s) or the viral genome in the glomerulus or viral particles identified on ultrastructural examination.
The absence of other causes of renal disease.
Regression of the pathologic lesion with viral eradication.
Reproducibility of the pathology in animal models infected with the virus.
Observations from chronic hepatitis virus infection in woodchucks revealed three types of glomerulonephritis, namely, membranous nephropathy with HBcAg deposits, mesangial proliferative glomerulonephritis with mesangial deposits of HBsAg, and mixed membranous and mesangial proliferative glomerulonephritis with capillary deposits of HBcAg and mesangial deposits of HBsAg. The natural animal model of woodchuck hepatitis reveals pathologic findings similar to those of humans. HBV-associated membranous nephropathy is particularly frequent in male children. Mesangial proliferative forms with IgA deposits appear to be more common in adults. In the woodchuck, the membranous pattern of injury appeared more frequently in the young, whereas the mesangial proliferative pattern of injury tended to appear in older animals. Nevertheless, in humans, it is difficult to rule out the chance occurrence of two common disorders (eg, HBV and IgA nephropathy) presenting in the older population in an endemic area as a cause of this association. The male/female ratio of affected woodchucks was significantly greater than that of the chronic carrier population. One major difference is that the HBeAg system has not been characterized in woodchucks. In clinical practice, regression of the pathology with viral eradication is not easily demonstrable because of ethical concerns involving repeat renal biopsies in human subjects after clinical remission. Hence the diagnosis of HBV-associated renal disease in reality relies heavily upon the demonstration of HBV-specific antigen(s) in the glomeruli.
Pediatric and adult patients tend to have slightly different clinical manifestations of HBV-related MN. In children, there is a strong male preponderance, and the most frequent presentation is nephrotic syndrome together with microscopic hematuria and normal or mildly impaired renal function. Pediatric chronic HBV carriers often do not have overt liver disease, and transaminase levels are usually normal. In adults, proteinuria and the nephrotic syndrome are the most common manifestations, though male predominance is less obvious than that observed in children. In addition, adults are more likely than children to have hypertension, renal dysfunction, and clinical evidence of liver disease.
The prognosis of HBV-associated MN in children is favorable with stable renal function and high rates of spontaneous remission reported in several high prevalence areas, including Hong Kong, South Africa, and Turkey. On the other hand, adults with HBV-associated MN typically develop progressive disease. In Hong Kong, up to 29% of patients had progressive renal failure, and another 10% developed ESRD over 5 years. The prognosis is even worse in patients with nephrotic-range proteinuria and overt hepatitis at presentation, with over 50% of patients requiring renal replacement therapy over 3 years.
Laboratory tests to be followed for diagnostic purposes and also to assess response to treatment include standard liver biochemistries (serum alanine aminotransferase, γ-glutamyltransferase, and bilirubin levels) and HBV serologies (HBsAg, HBeAg, anti-HBe, and anti-HBc antibodies). HBeAg is present in 80% of patients, who may also have high titers of anti-HBc. Subjects with biochemical hepatitis should also be tested for circulating HBV DNA levels and should undergo liver biopsy. In addition, α-fetoprotein assay could be an important adjunct. Serum C3 and C4 levels may be low in 20–50% of patients.
Light microscopic findings are similar to that of idiopathic MN, with some differentiating features. The characteristic glomerular lesion is a diffuse thickening of the glomerular capillary walls to form thick “membranes” (Figure 35–8A). It is now firmly established that this alteration is caused by immune complexes that accumulate subepithelially on the outer aspect of the GBM, which assumes a “membranous” morphology in a stepwise manner. Other pertinent light microscopic findings are reflected in the reactive structural changes of the GBM induced by immune complexes. Therefore special stains highlighting the GBM, such as methenamine silver and periodic acid–Schiff (PASM or silver stain) or trichrome stain, are more useful (Figure 35–8B). The earliest change on silver staining is a mottled appearance best seen on tangential sections and represents slight indentations of the GBM by immune complexes adhering to its surface. The most specific change of the GBM is the so-called “spike” formation (Figure 35–8C). These are projections of GBM material between immune complexes that lead to a saw tooth-like appearance of the GBM. This pattern is pathognomonic of full-blown membranous glomerulonephropathy. Disease progression results in a diffuse thickening of the GBM. The major constituents of the immune complexes are IgG together with C3. IgM, IgA, and C1q may be present. Ultrastructural findings typically consist of both subepithelial and occasional subendothelial deposits. The presence of subendothelial deposits, sometimes referred to as membranoproliferative glomerulonephritis type III changes, favors a secondary case of MN such as HBV associated rather than idiopathic. The presence of mesangial proliferation on light microscopy is helpful in distinguishing this form of secondary MN from idiopathic MN.
Pathology of hepatitis B virus (HBV)-associated membranous nephropathy (MN). A: On light microscopy, the characteristic glomerular lesion is a diffuse thickening of glomerular capillary walls to form thick “membranes” (H&E, ×200). B: Periodic acid–Schiff and methenamine silver staining highlight the characteristic epimembranous “spike” formation (arrow), projections of glomerular basement membrane (GBM) material between immune complexes that lead to a saw tooth-like appearance of the GBM (×400). C: Immunofluorescence reveals granular deposits of IgG (shown here) together with C3. IgM, IgA, and C1q may be present. D: Ultrastructural findings typically consist of both subepithelial (arrows) and occasional subendothelial (arrowheads) deposits. The presence of subendothelial deposits, sometimes referred to as membranoproliferative glomerulonephritis (MPGN) type III changes (an amalgam of membranous and MPGN type I pathologies), favors a secondary case of MN, such as HBV-related rather than idiopathic. (Courtesy of Dr. Yun-hoi Lui and Dr. Chung-ying Leung, Department of Pathology, United Christian Hospital, Hong Kong, China.)
Apart from MN, other renal pathologies have also been associated with HBV infection. These include MPGN with or without cryoglobulinemia, mesangial proliferative glomerulonephritis, and IgA nephropathy. Polyarteritis nodosa has also been reported in some patients with HBV and may respond to corticosteroids and interferon-α therapy. Occasionally, overlapping of these pathologic forms leading to double glomerulopathies may be seen. For instance, MN and IgAN have been reported to coexist in an HBV carrier.
Regardless of the pathologic finding, it is important to localize HBV-specific antigens in the biopsy. To document an etiologic association between HBV and MN or other forms of glomerular lesion, the demonstration of HBV-specific antigens by immunofluorescence is indispensable. The three major antigens are HBsAg, HBeAg, and hepatitis B core antigen (HBcAg). Monoclonal antibodies recognize a single antigenic epitope and are in general less sensitive than polyclonal antibodies that bind to more than one epitope. Commercial polyclonal anti-HBc preparations cross-react with both anti-HBc and anti-HBe, as HBeAg is an integral component of HBcAg. HBsAg is characteristically localized in the mesangium while HBeAg is found in the capillary loop. Furthermore, HBV DNA and mRNA have been detected in the glomerulus and tubular epithelia by polymerase chain reaction and in situ hybridization with specific HBV RNA probes.
Unlike childhood disease in which there is a high rate of spontaneous remission, adults with HBV-associated MN typically develop progressive disease. Various strategies have been tried, although an ideal agent has yet to be found. Treatment for HBV-associated renal disease should ideally achieve the following objectives:
Amelioration of nephrotic syndrome and its complications, such as hyperlipidemia, edema, infection, and venous thrombosis.
Preservation of renal function.
Normalization of liver function and prevention of hepatic complications of HBV.
Permanent eradication of HBV.
In view of the immune complex nature of the disease, immunosuppressive therapy, similar to that applied in the idiopathic form of the disease, was once fashionable. Although it has previously been reported that corticosteroids achieve symptomatic relief in isolated cases, the contemporary view is that steroids and cytotoxic agents may cause deleterious hepatic flares or even fatal decompensation by enhancing viral replication upon treatment withdrawal.
Another approach is treatment with an antiviral agent. Interferon-α is a naturally occurring cytokine produced by B-lymphocytes, null lymphocytes, and macrophages, and possesses antiviral, antiproliferative, and immunomodulatory effects. While reported to be useful in children, interferon-α has produced mixed results in adults with HBV-associated MN.
The introduction of the nucleoside analog lamivudine has revolutionized the treatment of chronic HBV infection. Lamivudine is the (–)-enantiomer of 3′-thiacytidine, and it inhibits DNA synthesis by terminating the nascent proviral DNA chain through interference with the reverse transcriptase activity of HBV. In children and adults with HBV-associated MN, lamivudine has been anecdotally reported to induce remission of nephrotic syndrome and suppress viral replication. In our analysis of 10 adult nephrotic patients with HBV-related MN who received lamivudine treatment versus 12 matched historic control subjects who presented in the prelamivudine era, lamivudine treatment significantly improved proteinuria, ALT levels, and renal outcome over a 3-year period (Figure 35–9). Randomized studies in a larger cohort of patients are needed. A potential limitation of prolonged treatment with lamivudine is the emergence of drug-resistant strains due to the induction and selection of HBV variants with mutations at the YMDD motif of DNA polymerase. One agent that might be considered in case of lamivudine resistance is adefovir dipivoxil, an acyclic nucleotide analogue that is effective against both lamivudine-resistant HBV mutants as well as wild-type HBV. However, this agent is potentially nephrotoxic and there are no clinical data on its efficacy in HBV-related MN that does not respond to lamivudine treatment. There are data to suggest that the recommended dose of 10 mg adefovir dipivoxil is associated with a lower risk of nephrotoxicity.
Renal survival in 10 patients who received lamivudine treatment for hepatitis B virus-associated membranous nephropathy (solid line) versus 12 matched patients from the prelamivudine era (dotted line).
In the absence of an ideal agent for treatment of HBV-associated glomerulopathy, active immunization remains the most effective measure of immunoprophylaxis. Vaccination for all newborns in some endemic areas such as Hong Kong has dramatically reduced the incidence of chronic HBV infection and its associated complications in children and adolescents. In Taiwan, the introduction of active immunization to all newborns since 1984 has led to a dramatic (10-fold) decline in the incidence of neonatal HBV infection and its subsequent sequelae. In the United States, universal vaccination of infants began in 1991, and a 67% reduction in HBV infection was recorded 10 years later. In 2003, the World Health Organization recommended that all countries provide universal HBV immunization programs for infants and adolescents.
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