Microscopic polyangiitis pathophysiology

The pathogenesis of microscopic polyangiitis is currently not fully understood. However, certain hypothesizes have been made to determine possible factors that may trigger the disease such as environmental factors and anti-neutrophil cytoplasmic antibodies. Capillaries and venules are involved in the pathogenesis of microscopic polyangiitis.The paucity of immunoglobulin deposition is shown in immunohistochemical staining.

• The exact etiology of Microscopic polyangiitis is not fully understood.
• Certain hypothesizes have been made to determine possible factors that may trigger the disease.
• Triggers such as environmental factors and anti-neutrophil cytoplasmic antibodies.

• Environmental triggers such as exposure to silica have been found to influence the progression of the disease.But, its role in disease progression is not fully understood.^[1]

Key-points regarding ANCA in microscopic polyangiitis include:^[2][3][4][5]

• The majority of patients who are affected with microscopic polyangiitis are positive for anti-neutrophil cytoplasmic antibodies (ANCA) with myeloperoxidase antigen activity.
• The presence of anti-neutrophil cytoplasmic antibodies (ANCA) activates neutrophil production do to proinflammatory cytokines such as interleukin-1 and tumor necrosis factor-α (TNF-α).
• Stimulation of interleukin-1 and tumor necrosis factor-α (TNF-α) results in producing reactive oxygen species and causing the release of lytic enzymes.
• These two processes, induce detachment and lyses of the endothelium.
• The destruction of the endothelial cells results in necrotizing crescentic glomerulonephritis and necrotizing vasculitis of the pulmonary capillaries.^[6]

• Microscopic polyangiitis is correlated with HLA-DRB1*09:01-DQB1*03:03 haplotype in the Japanese population. This haplotype however, in the Caucasian population is not typically seen.^[7]

• On gross pathology, the characteristic findings of microscopic polyangiitis incude:^[8][9]
  • Hemorrhagic necrotizing alveolar capillaritis
  • Fibrinoid necrosis of the lung
  • Intra-alveolar hemosiderosis

• On microscopic histopathological analysis of the kidney in patients with microscopic polyangiitis, characteristic findings include:^[10][11]
  • Focal segmental necrotizing glomerulonephritis
  • Crescents of glomeruli
  • Minimal deposition of immunoglobulins
  • Compliment in glomeruli and renal vasculature can be seen

• The majority of patients who are affected with Microscopic polyangiitis are positive for anti-neutrophil cytoplasmic antibodies (ANCA) with myeloperoxidase antigen activity.
• The presence of anti-neutrophil cytoplasmic antibodies (ANCA) activates neutrophil production do to proinflammatory cytokines such as interleukin-1 and tumor necrosis factor-α (TNF-α).
• Stimulation of interleukin-1 and tumor necrosis factor-α (TNF-α) results in producing reactive oxygen species and causing the release of lytic enzymes.
• These two processes, induce detachment and lyses of the endothelium.
• The destruction of the endothelial cells results in necrotizing crescentic glomerulonephritis and necrotizing vasculitis of the pulmonary capillaries.^[12]

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