In 1977, Y. Levo and his coworkers firstly described the association between HBV infection and MC [1]. It has been established that HBV is a rare infectious etiology of MC, compared with HCV infection. It was unknown what percentage of patients with chronic HBV infection may develop CV. A search of the literature revealed few studies focusing on CryoGn associated with HBV infection. Our retrospective study described the spectrum of clinical presentations and pathological features of seven Chinese patients with HBV related CryoGn, as well as their response to therapy and renal outcome.
We found that CryoGn associated with HBV were commonly associated with type II cryoglobulins. This finding was consistent with that of Italian study which reported type II cryoglobulins accounted for 88% in HBV related cryoglobulinemic vasculitis[5]. However, result in another previous Chines study suggested that type III cryoglobulinemia was more frequently seen in HBV related CryoGn[6]. This discrepancy may reflect differences in the laboratory methods in detection of cryoglobulin as well as patient selection bias considering a limited sample size. The most common extrarenal manifestation was cutaneous lesions (6/7) in our study, while other organs were seldom involved. Considering that only one case with Type III MC was included in our study, we were not able to conclude that clinical manifestation of the vasculitis is more frequently in Type II MC than in Type III MC reported in the literature[7].
Nephrotic syndrome was the most common syndrome with microscopic hematuria in our included patients. Acute renal injury or chronic renal insufficiency also occurred in most patients and some of them presented as RPGN and needed renal replacement therapy. We found HBsAg in the cryoprecipitate in two of our patients, confirming the pathogenic role of HBV in cryoglobulinemia.
CryoGn with a membranoproliferative pattern of injury was mostly reported in the literature, no matter what etiology it is[8, 9]. Our data demonstrated that endocapillary proliferative Gn was also the common morphologic type on light microscopy, as well as membranoproliferative Gn. The morphologic pattern of HBV related CryoGn varied in the limited number of previous studies. Membranous nephropathy was the predominant pattern reported in one study including eight Chinese cases of CryoGn associated with HBV infection[10], while the result of another Chinese study demonstrated that membranoproliferative GN was the exclusive type of all 12 patients[6]. The discrepancy of the morphologic pattern of CryoGn among different studies could have been generated by a limited sample size. Hyaline thrombi were characteristic findings of CryoGn on light microscopy but inconsistently occurred in our study. And we didn’t find the association between the nephritic syndrome and the presence of hyaline thrombi.
On immunofluorescence microscopy, mesangial and capillary wall deposits of immunoglobulins (IgM, IgG or IgA) and C3 were found in most of the patients, which indicated the subendothelial location of deposits. However, it was notable that HBsAg and HBcAg staining were positive only in one patient in our study, which was similar to the results of a previous study[10]. We don’t find the specific reason for the absence of HBV antigen deposition in glomeruli in most patients with CryoGn associated with HBV infection. It is possible that circulating immune complexes of HBV antigen and antibodies plays a less important role than cryoglobulins in the pathogenesis of CryoGn. Another possible explanation for these results may be that cryoglobulins interfere combination between antigen and antibody, which decreased the sensitivity of immunofluorescence staining of HBsAg and HBcAg.
Diagnostic features for CryoGn by electron microscopy include microtubular, fibrillary, and crystal structure, but these structures are not always observed[8]. Moreover, these features are not specific to the etiology of CryoGn. All the included patients in our study had granular electron-dense deposits located in the subendothelial region. We observed microtubule structure in only one case on electron microscopy. These findings were consistent with the ultrastructural features of HBV related CryoGn reported in the literature[6, 10]. In one previous study including 12 patients of CryoGn associated with HBV infection, only two cases were found microtubule substructure on electron microscopy[6].
The optimal treatment for HBV-associated CryoGn is not known since there is no randomized trial. This is probably due to the uncommon occurrence of HBV-associated cryoglobulinemic vasculitis. Several studies confirmed a correlation between HBV suppression and CV regression after nucleoside analogs (NAs) therapy[5, 11, 12]. These findings support the hypothesis that HBV replication plays an important role in the CV etiopathogenesis. Among different NAs, entecavir is preferred given its antiviral efficacy, low propensity for drug resistance, as well as low risk for nephrotoxicity[13]. Considering limited data and potential side effects, interferon-alfa is not recommended for the treatment of HBV-associated CryoGn[5]. In our study, most of the patients (6/7) received entecavir. And three patients with elevated HBV-DNA at baseline were well controlled and HBV-DNA was undetectable at the endpoint of our study.
The studies in the literature demonstrated that NAs therapy in HBV-related CV yields high virologic and satisfying clinical responses in most patients with mild-and-moderate CV, but a low response in the severe CV. For patients with severe disease, immunosuppressive therapy is recommended, based on efficient antiviral therapy to prevent HBV reactivation[14]. Immunosuppressive therapy targets the inflammatory cells involving in the pathogenesis of vasculitis. In our study, five patients’ eGFR improved and four of them achieved complete or partial remission after receiving immunosuppressive therapy. Their renal outcomes were favorable during follow-up. Notably, using corticosteroids without NAs is associated with refractory or relapsing disease. The Number Seven case in our study initially received corticosteroid and cyclophosphamide without antiviral therapy in a local hospital which led to HBV reactivation and kidney disease relapse. He had a poor response to therapy and progressed to ESRD during follow-up. Although one case report described the efficacy and safety of rituximab in HBV-related CryoGn[15], no patients in our study were received this biologic considering the potential risk of HBV reactivation. Moreover, the side effect of conventional immunosuppressive therapy, such as severe infection, should be considered before using it especially in elderly patients with renal insufficiency. During follow-up, two patients died from pneumonia although there was no evidence of bone marrow suppression.
Two patients in our study received plasmapheresis to remove circulating cryoglobulins. Although we didn’t find the significant association between eGFR level and the concentration of cryoglobulins, their eGFR improved accompanied by cryoglobulin level decline after six or eight sessions of plasmapheresis during hospitalization. Limited data in the literature suggested clinical improvement in CV patients with severe organ involvements after plasmapheresis[16–18]. A multicenter retrospective study in Italy recommended plasmapheresis in patients with severe CV, especially in cases with acute kidney injury, to prevent irreversible lesions[19]. Considering that plasmapheresis doesn’t inhibit the generation of new cryoglobulins, it is rational to combine with other immunosuppressive therapy to reduce the production of cryoglobulins.
The major limitations of our study include the small sample size and relatively short follow-up time. All patients in our study had normal liver function without cirrhosis evidence. Therefore, caution must be applied, as the findings and immunosuppressive therapy in our study might not be transferable to HBV patients of CryoGn with evidence of active hepatitis or severe cirrhosis. Further prospective studies are needed to evaluate the efficacy and safety of corticosteroid or immunosuppressors in patients with HBV related CryoGn.