Microscopic polyangiitis is a systemic necrotizing vasculitis that primarily involves small blood vessels and may invade small arteries, microarterioles, capillaries, and small veins in organs such as the kidney skin and lungs. It often manifests as necrotizing glomerulonephritis and pulmonary capillaritis.In 1948, Davson et al. first proposed that there exists a subtype of polyarteritis nodosa characterized by segmental necrotizing glomerulonephritis, which is called microscopic polyarteritis (MPA), because it mainly involves small blood vessels, including veins, and is therefore now called microscopic polyangiitis.In 1990, the classification of vasculitis by the American College of Rheumatology did not include MPA in its criteria. The 1990 American College of Rheumatology classification of vasculitis does not list MPA separately, so in the past, microscopic polyangiitis was mostly classified as polyarteritis nodosa and rarely as Wegener’s meat. Microscopic polyangiitis can develop at any age, but it is most common in the age group of 40-50 years old, with a prevalence rate of 1 in 100,000-3 in 100,000 people, and the rate of males is slightly higher than that of females, with the ratio of males to females being 1 to 1 or 8:1. Clinical manifestations Microscopic polyangiitis has a variable onset and a rapidity. The onset of microscopic polyangiitis (MPA) varies: MPA may present acutely with acute glomerulonephritis, pulmonary hemorrhage, and hemoptysis, or it may be very insidious, with intermittent purpura, mild renal damage, and intermittent hemoptysis over the course of several years. Typical cases have skin-lung-kidney clinical manifestations. 1, systemic symptoms. Patients with microscopic polyangiitis (MPA) often present with a general systemic condition, including fever, malaise, anorexia, arthralgia, and weight loss. Skin manifestations: MPA may present with various skin rashes with purpura and congestive maculopapular rash above the skin surface. Rash can appear alone or with other clinical symptoms at the same time, and its pathology is mostly leukocyte crushing vasculitis. In addition to the rash, patients with MPA may also present with reticular cyanotic spots, skin ulcers, skin necrosis, gangrene, and limb ischemia, necrotic nodules, urticaria and vasculitis-associated urticaria often lasting for more than 24h. 3.Renal damage. Renal damage is the most common clinical manifestation of MPA, the lesion performance varies greatly, and very few patients may have no renal lesions. Most patients have proteinuria, hematuria, tubular edema and renal hypertension; some patients have renal insufficiency, which may progressively deteriorate to renal failure. 25% to 45% of patients eventually need hemodialysis. The renal pathology of MPA is necrotizing glomerulonephritis, which is characterized by segmental necrosis with crescent formation and little or no capillary endothelial cell proliferation. Glomerular histology with little or no immune complex deposition electron microscopy with little or no electron dense material deposition. The above features are different from other immune complex-mediated glomerulonephritis and anti-glomerular basement membrane antibody-mediated Goodpasture’s syndrome, but are not easily differentiated from the renal lesions of Wegener’s granulomatosis and the idiopathic acute glomerulonephritis at times.Pathologic changes on light microscopy of MPA are seen. 4, lung damage. About half of the patients with MPA have lung damage occurring alveolar capillaritis, 12% to 29% of patients have diffuse alveolar hemorrhage. Examination of the lungs can be seen in respiratory distress signs can be smelled woven mat S piggyback shirking to the edge of the M we wash yatou Bangde word (11) to go to the M tail copy hydra 1/3 of the patients appeared coughing, hemoptysis, anemia, which a large number of pulmonary hemorrhage can lead to respiratory distress, or even death. Some patients may develop interstitial fibrosis on the basis of diffuse alveolar hemorrhage. 5, Nervous system: 20% to 30% of MPA patients have symptoms of neurological damage, of which about 57% have multiple mononeuritis or polyneuropathy, and about 11% of patients may have central nervous system involvement, often manifested as seizures. 6. Digestive system. The digestive tract can also be involved, manifesting as gastrointestinal bleeding, pancreatitis, and abdominal pain caused by intestinal ischemia. In severe cases, ischemia can be caused by small vessel inflammation and thrombosis in the gastrointestinal tract, resulting in intestinal perforation. 7, cardiovascular system: MPA can also involve the cardiovascular system, patients may have chest pain and heart failure symptoms, clinical hypertension, myocardial infarction and pericarditis. 8. Others. Some patients also have ear, nose and throat manifestations, such as sinusitis, it is easier to be confused with Wegener’s granulomatosis. A few patients may also have arthritis arthralgia and testicular pain due to orchitis. Ocular symptoms include redness, swelling, and pain in the eyes, as well as loss of vision. Ophthalmologic examination reveals retinal hemorrhage, scleritis, and uveitis. Diagnosis There are no standardized criteria for the diagnosis of this disease, but in the presence of systemic damage with pulmonary involvement and renal involvement and the presence of purpura above the skin surface, the diagnosis of MPA should be considered, especially if there is also a positive p-ANCA. Renal biopsy and skin or other visceral biopsy are useful in the diagnosis of MPA. In some patients, infective endocarditis should be excluded. Laboratory tests 1, routine examination: in MPA, indicators reflecting acute phase inflammation such as ESR, CRP is elevated, some patients have anemia leukocytes and thrombocytosis. Proteinuria, microscopic hematuria and erythrocyte tubular pattern, elevated serum creatinine and urea nitrogen levels are seen when the kidney is involved. 2. Immunologic examination: C3 and C4 levels are normal. About 80% of MPA patients are positive for anti-neutrophil cytoplasmic antibodies (ANCA), which is an important diagnostic basis for MPA. About 60% of them are positive for MPO-ANCA (p-ANCA), which is often found in those with lung involvement, and about 40% of them are positive for PR3-ANCA (c- ANCA). Anti-cardiolipin antibodies (ACL) can be detected in about 40% of patients, and a small number of patients are positive for ANA and RF. Peking Union Medical College Hospital 1995-2001 diagnosed 16 cases of MPA patients in ANCA positive 13 cases (81,2%), of which 11 cases (84,6%) for P-ANCA positive, 3 cases (23,1%) c-ANCA positive patients in 1 case (7,7%) at the same time p-ANCA positive. 3, chest radiograph: early can be found without characteristic bilateral irregular nodular flaky shadow or small vesicular infiltration shadow, lung cavity is rare, can be seen secondary to alveolar capillaritis and pulmonary hemorrhage diffuse lung parenchyma infiltration shadow, interstitial fibrosis can appear in the middle and late stages of the lung. The clinical manifestations of MPA vary, with some showing only mild systemic vasculitis and mild renal failure, while others have an acute onset, with an aggressive condition that rapidly progresses to renal failure and respiratory failure due to pulmonary capillary alveolitis. Therefore, the treatment of this disease is mainly based on the extent and progression of the disease and the degree of inflammation. The treatment of MPA can be divided into 3 stages, stage 1 is induction of remission; stage 2 is maintenance of remission, which can be treated with medium-dose prednisone and maintenance cyclophosphamide (CTX) for 12 months, or switch to azathioprine, methotrexate and other DMARDs to maintain the remission; stage 3 is the treatment of relapse, which can be treated with the same treatment regimen as that of induction of remission, which can be associated with the colonization of S. aureus and the recurrence of MPA. There is a relationship between the recurrence of MPA, so the administration of sulfonamide antibiotics is effective in preventing recurrence. Patients with life-threatening alveolar capillaritis with pulmonary hemorrhage should be treated with combination therapy or plasmapheresis. Glucocorticoid plus cyclophosphamide should be the first choice. Glucocorticosteroids Glucocorticosteroids are the first-line drugs for treating MPA and inducing remission. In order to induce remission as soon as possible, methylprednisolone (methylprednisolone) shock therapy can be used, the dose of 7mg/(kg・d), for 3 days, and then switch to prednisone to gradually reduce the dose. The initial dose of prednisone was 40～60mg/d. After the ESR was reduced to normal and the patient’s symptoms disappeared, the dose was reduced by 5～10mg every 1～2 weeks. when the dose was reduced to 15mg, the reduction should be slow. Primary treatment, especially with pulmonary and renal damage, commonly used prednisone 60mg/d, and combined with cyclophosphamide, the course of treatment should be long, after stopping the drug, there are still about 25% of the patients in the average recurrence within 24 months. 2, immunosuppressant (1) cyclophosphamide (CTX): cyclophosphamide should be used as the first choice of treatment, the dose of intravenous administration of 0,5 ~ 1g / (m2・month), or 0,2g intravenous injection every other day, or 0,1g oral 1 time / d. Adjustment of dosage according to the leukocyte count in the course of the medication, the duration of the drug should be long, usually up to 12 months. (2) Methotrexate (MTX): MTX can inhibit inflammation and reduce inflammatory symptoms. The dose is 10-25mg/week, orally, intramuscularly and intravenously. (3) Azathioprine: now the commonly used dosage is azathioprine (Imuran), an antagonist of purine metabolism, which can inhibit the synthesis of DNA and RNA, thus reducing the proliferation of immune cells, down-regulation of immunoreactive dosage of 1mg/(kg・d), commonly used 50-100mg per day. after 6-8 weeks of use, if the initial dose is ineffective, the dosage can be increased if there are no serious adverse effects. The dose should be increased at the rate of 0.5mg/(kg・d), and the total dose should not exceed 2.5mg/(kg・d) if necessary, and the dose can be adjusted every 4 weeks. 3.Intravenous Human Gammaglobulin(Gammaglobulin) Patients with poor response to cyclophosphamide treatment can use intravenous human Gammaglobulin, which can significantly improve the clinical symptoms of pulmonary and renal damage, and the anti-unique antibody may be an effective mechanism of action.The dose of IVIg is 400mg/(kg・d) for 5-7 days, and the commonly used dosage is 20g/d in China.