Vasculitis de pequeño vaso

Small-vessel vasculitides are a group of inflammatory diseases that affect arterioles, capillaries, and venules, classified by Chapel Hill nomenclature (2012). They include immunocomplex-mediated vasculitis (IgA vasculitis, cryoglobulinemic vasculitis, hypocomplementemic urticarial vasculitis) and vasculitides associated with anti-neutrophil cytoplasmic antibodies (ANCA) or anti-glomerular basement membrane antibodies (anti-GBM). These diseases have heterogeneous immunopathological mechanisms with multisystem involvement. IgA vasculitis, prevalent in children, is associated with IgA deposits in small vessels, frequently triggered by respiratory infections. Its manifestations include palpable purpura, arthritis, abdominal pain, and nephritis, the latter being the main determinant of the prognosis. Cryoglobulinemic vasculitis is usually associated with hepatitis C or autoimmune diseases. It manifests as purpura, neuropathy, arthralgias, and glomerulonephritis. Its treatment combines antivirals, glucocorticoids, and immunotherapy such as rituximab. Hypocomplementemic urticaria vasculitis includes persistent urticaria-like lesions, hypocomplementemia, and anti-C1q antibodies, with renal and pulmonary involvement in severe cases. Microscopic polyangiitis (MAP), associated with ANCA, mainly affects the kidneys and lungs, causing necrotizing glomerulonephritis and alveolar hemorrhage. Anti-GBM vasculitis is rare. It is characterized by autoantibodies that target collagen IV. It manifests as a lung-kidney syndrome with alveolar hemorrhage and rapidly progressive glomerulonephritis. Its diagnosis combines symptoms, immunology, and histopathology. Management depends on the severity and organs involved and prolonged follow-up is key.