Systematic review of mixed cryoglobulinemia associated with hepatitis E virus infection: association or causation?

Background and aim: Mixed cryoglobulinemia (MC) has been associated with several viral infections, and chronic hepatitis C is recognized as a major cause. MC associated with hepatitis E virus (HEV) has been described and little is known about this rare association. The aim of this study is to perform a systematic review of MC associated with HEV, and examine the presence of a causal relationship. Methods: An experienced librarian conducted a search of databases from each database's inception to 12 December 2016 based on a priori criteria. The risk of bias was assessed, and Hill's criteria were applied to determine causality. Results: Five publications met inclusion criteria, with a total of 15 cases. Three studies had low, one low to moderate and one moderate risk of bias. Median age was 43 years, and all patients came from Western Europe. Two patients were immunocompetent, while 13 were immunosuppressed, post solid organ transplant and had chronic hepatitis E. Renal involvement was observed in seven patients, mild to moderately severe cryoglobulinemic disease in one patient and severe cryoglobulinemic disease in three patients. One patient improved spontaneously, and another was treated with immunosuppressant reduction leading to viral clearance. Ten patients treated with peg-interferon or ribavirin for 3 months achieved loss of cryoglobulinemia and end-of-treatment response, but sustained virologic response was reported and achieved in two. Immunosuppressant achieved loss of cryoglobulinemia in three patients. One case of chronic renal failure, three cases of end-stage renal disease and one death were observed. Five of the nine Hill's criteria were fulfilled. Conclusion: MC has been described with HEV infection. A causal relationship between HEV infection and cryoglobulinemia is highly probable.