The term «monoclonal gammopathies of undetermined significance» (MGUS) was introduced by R. Kyle in 1978 to designate the condition characterized by the presence ofsmall amounts ofM-protein in the serum. In some patients, such condition remains benign for a long time but predetermines for the development of multiple myeloma and other B-lymphocytic tumours. Also, it can provoke non-cancerous diseases due to the toxic action of monoclonal proteins (immunoglobulins and free light chains) on various organs, especially kidneys. MGUS-associated renal lesions include glomerulopathies with organized deposits, such as AL-amyloidosis (amyloid light chain of immunoglobulin), cryoglobulinic and immunotactoid glomerulonephritis, and with unorganized deposits (light chain deposition and proliferative forms of idiopathic glomerulonephritis. The available experimental data throw light on the possible mechanisms of renal lesions. We summarized the literature data and original observations to describe methods for differential diagnostics of MGUS-associated renal lesions including the highly sensitive test for free light chine identification (Freelite method) and principles of pathogenetic treatment by the impact on the pathological B-cell clone.

HCV-associated CV can determine the prognosis of chronic HСV infection. AVT is the treatment of choice in all patients with HСV-associated CV. AVT must be combined with rituximab therapy in patients with severe forms of vasculitis.

Aim. To evaluate the results of immunosuppressive and/or antiviral treatment of patients with hepatitis C virus (HCV)-induced mixed cryoglobulinemic (MC) vasculitis. Material and methods. This prospective study included 60 patients (m/f - 23/49, age - 45,9±11,1) with HCV-MC vasculitis. The Birmingham vasculitis activity score (BVAS) was used before the treatment and during follow-up (3,5±4,1 years). The rate of clinical and immunological responses to the treatment, the frequency of relapses and the influence of different treatment approaches on the prognosis of the disease were evaluated. Logistic regression analysis was used to assess factors influencing the effectiveness of treatment. Results. 23 (38%) patients had liver cirrhosis. BVAS scores before treatment ranged from 2 to 36. 25 (41,6%) patients had BVAS≥15. 6 (10%) patients presented with B-cell non-Hodgkin lymphomas. The antiviral treatment resulted in the elimination of the virus in 48.0% of the cases, complete clinical and immunological responses were achieved in 68,0% and 32,0% respectively. It had an advantage over immunosuppressive therapy in terms of long-term results of the treatment. We established the superiority of anti-CD monoclonal antibodies (rituximab) over conventional immunosuppressive drugs: complete clinical response 73% vs 13% (p=0,001). Combined therapy (rituximab and antiviral treatment) was more effective in patients with severe vasculitis (BVAS≥15). A case of successful treatment using direct-acting antivirals (DAAs) is reported. Causes of MC-vasculitis relapses after achieving sustained viral response are discussed. Conclusion. Antiviral therapy is the treatment of choice in all patients with HCV- HCV-MC vasculitis. Preference should be given to highly effective and safe modern therapy regimens with the use of DAAs. The antiviral treatment of severe forms of vasculitis must be combined with rituximab therapy.

A case of rapidly progressive glomerulonephritis in a 17-year-old patient associated with antibodies against the cytoplasm of neutrophils (ANCA) vasculitis - ANCA-associated vasculitis is associated with antibodies to proteinase-3 and morphological picture extracapillar glomerulonephritis with sclerotic lesion of up to 80% of the glomeruli. The peculiarity of the case is the presence of morphologically confirmed when alloimmune rapidly progressive glomerulonephritis type III a pronounced glow-focal granular nature of immunoglobulin classes G and M on the basement membrane of capillaries. The appointment of immunosuppressive therapy led to a decrease in systemic manifestations of vasculitis, but there was a rapid increase in terminal renal failure, which required substitution therapy with hemodialysis. The possible mechanisms of the rapid-training course of the disease in the observed patient, prospects for kidney transplantation are discussed.

The extrahepatic manifestations of HCV infections, which include mixed cryoglobulinemia (MC), are important for prognosis and determination of the treatment options of these patients. Currently, mixed MC type II is considered as a specific marker of chronic HCV infection. Kidney damage is one of the severe, often determining a prognosis of extrahepatic manifestation of HCV-associated cryoglobulinemic vasculitis. The review discusses the current diagnostic approaches to cryoglobulinemic GN, as well as perspectives for improving antiviral and pathogenetic therapy.