Microscopic polyangiitis is a small vessel vasculitis that affects the skin, lungs and kidneys. Blood vessel inflammation under the skin causes the development of palpable purpura. Involvement of the lungs can lead to hemoptysis, and involvement of the kidney leads to hematuria. On renal biopsy, a rapidly progressive or crescentic glomerulonephritis is seen, and immunofluorescence reveals a pauci-immune or negative pattern. Importantly, patients with microscopic polyangiitis will often test positive for MPO-ANCA or p-ANCA. Treatments for microscopic polyangiitis include cyclophosphamide and corticosteroids.