Type II essential mixed cryoglobulinemia and renal disease. Hepatitis C virus association

Recently a number of studies have implicated C virus as a major cause of mixed cryoglobulinemia. Several authors described that up to 95% of "essential" mixed cryoglobulinemia could be attributed to this viral infection. Nevertheless, its prevalence and clinical significance are not well known. We review our experience in relation with the clinical, biological and evolutive characteristics of patients diagnosed of type II mixed cryoglobulinemia. METHODS: Descriptive and protocolized study of all cases found to have type II mixed cryoglobulinemia over a period of 8 years. Secondary cryoglobulinemic nephropathy was defined in a restrictive way: a plasma creatinine > 1.5 mg/dl and/or proteinuria > 500 mg/24 h and/or hematuria (> 15 red blood cells) need to be present in the absence of any other pathological conditions that could justify these alterations. Furthermore, the information obtained from available kidney biopsies was considered. RESULTS: 62 patients have been detected. C virus infection was demonstrated in 44 (72%). 52% had clinical symptoms related with cryoglobulinemia. 56% had alteration of renal tests, and 17 (27%) fulfil the conditions for the diagnosis of cryoglobulinemic nephropathy (nearly all with persistent microhematuria, median proteinuria 4.2 +/- 3.9 g/24 h; median plasma creatinine 2.8 +/- 1.8 mg/dl). Nine patients had been histologically examined, showing 6 cases a membranoproliferative glomerulonephritis pattern, one with associated extraglomerular vasculitis; two with mesangial proliferative pattern and one with membranous glomerulonephritis. The most striking differences between cryoglobulinemic nephropathy patients and the rest has been: higher amount of cryoglobulins (49 +/- 28 vs 20 +/- 22); more frequent hypocomplementemia, especially C4 (93% vs 59%) and recurrent purpura (75% vs 32%). No differences in the presence of C virus infection could be observed (75% vs 71%). IN CONCLUSION: 72% of patients with type II mixed cryoglobulinemia are infected by C virus (so 28% in our serie are "essential"); 52% have symptoms related with the presence of cryoglobulins, half of them with cryoglobulinemic nephropathy.