Microscopic Polyangiitis: from Pathogenesis to Treatment

Microscopic Polyangiitis (MPA) is a systemic pauci-immune necrotizing vasculitis of small-calibre vessels characterized by the absence of granulomas. MPA is an autoimmune disease but its aetiology remains obscure. MPA is associated with presence of antineutrophil cytoplasmatic autoantibodies (ANCAs) but not all patients with MPA have ANCAs. There is strong evidence that not all ANCAs are pathogenetic. It seems that specific epitopes determine ANCAs pathogenicity. Given that MPA is a systemic vasculitis, multiple organs could be affected resulting in a wide spectrum of signs and symptoms. The kidneys and lungs are the most typical organs involved in MPA. Notably, MPA is the major cause of pulmo-renal syndrome. MPA has a poor prognosis if not treated but the use of aggressive immunosuppressive treatment has improved the prognosis and the patient’s survival. Rituximab could be considered as an alternative treatment for severe disease, for patients who do not respond adequately to the immunosuppressive treatment and for patients with relapses. However, the long-term safety of Rituximab in MPA is unknown and it should be elucidated by further studies. Interestingly, kidney transplantation is safe and effective and it has a good prognosis in MPA patients with ESRD.