Microscopic polyangiitis

Microscopic polyangiitis - necrotizing vasculitis with or without minimal immune deposits, affecting small vessels (arterioles, capillaries, venules), less often the arteries of the middle caliber, with a predominance in the clinical picture of necrotizing glomerulonephritis and pulmonary capillaritis.

[1], [2], [3], [4], [5]

Epidemiology

At present, microscopic polyangiitis is registered almost 10 times more often than nodular polyarteritis. The incidence of microscopic polyangiitis is 0.36 per 100 000 population. Disease microscopic polyangiitis often develops at the age of 50-60 years, almost the same frequency in men and women.

[6], [7], [8], [9], [10]

Causes of the microscopic polyangiitis

The disease microscopic polyangiitis is described by J. Davson and co-authors. In 1948 as a separate variant of nodular polyarteritis, in which rare arterial hypertension, but there is focal necrotizing glomerulonephritis, indicating the lesion of small vessels. The form of the kidney lesion (segmental necrotizing small immune glomerulonephritis), which combines microscopic polyangiitis, Wegener's granulomatosis and rapidly progressive glomerulonephritis without extrarenal signs of vasculitis, confirms the validity of microscopic polyangiitis release into an independent nosological form different from nodular polyarteritis. Detection in the blood of patients with microscopic polyangiitis ANCA allowed this form of systemic vasculitis to be assigned to the group of ANCA-associated vasculitides, and glomerulonephritis in this form of vasculitis to the low-immune fast-progressing glomerulonephritis associated with the presence of ANCA (type III no R. Glassock, 1997).

The basic ideas about the role of ANCA in the pathogenesis of systemic vasculitis have been described in the description of Wegener's granulomatosis. Unlike the latter, in most patients microscopic polyangiitis in the blood is detected by pANCA against myeloperoxidase.

[11], [12], [13], [14], [15], [16]

Pathogenesis

A distinctive feature of microscopic polyangiitis is segmental necrotizing vasculitis of small vessels without signs of granulomatous inflammation. In addition to vasculitis of the vessels of the microcirculatory bed, necrotizing arteritis, histologically similar to that of nodular polyarteritis, can develop  . The most common are small vessels of the kidneys, lungs and skin.

• The skin is characterized by the development of dermal leukocytoclastic venuleum.
• In the lungs, necrotizing alveolitis with septal capillaritis, massive neutrophil infiltration develops. In the case of death of a patient from pulmonary hemorrhage during autopsy, hemosiderosis of the lungs is detected.
• In the kidneys, a morphological picture of focal segmental necrotizing glomerulonephritis with semilunals identical to glomerulonephritis in Wegener's granulomatosis is revealed. Unlike the latter, kidney lesions with microscopic polyangiitis are not characterized by interstitial granulomas and necrotizing vasculitis of efferent  vasa recta  and peritubular capillaries.

[17], [18], [19]

Symptoms of the microscopic polyangiitis

Symptoms of microscopic polyangiitis begin with fever, migratory arthralgia and  myalgia, hemorrhagic purpura, weight loss. About a third of patients in the debut of the disease suffer from ulcerative necrotic rhinitis. In contrast to Wegener's granulomatosis, the changes in the upper respiratory tract are reversible, not accompanied by destruction of tissues, and therefore do not lead to deformation of the nose.

When a biopsy of the nasal mucosa is not detected granuloma, and note only nonspecific inflammation. The manifestations of lesions of internal organs with microscopic polyangiitis and Wegener's granulomatosis are similar.

The prognosis determines the defeat of the lungs and kidneys.

• Lungs are involved in the pathological process in 50% of patients. Clinically,  hemoptysis, dyspnea, cough,  pain in the chest. The most dangerous symptom is pulmonary hemorrhage, which becomes the main cause of death of patients with microscopic polyangiitis in the acute period. X-ray reveals massive infiltrates in both lungs, signs of hemorrhagic alveolitis.
• Kidney damage is detected in 90-100% of patients with microscopic polyangiitis. It is manifested in most cases by the symptomatology of rapidly progressive glomerulonephritis with increasing renal failure, persistent hematuria and moderate proteinuria, which usually does not reach the nephrotic level. Arterial hypertension is expressed moderately and, unlike Wegener's granulomatosis, develops not often.

About 20% of patients, like Wegener's granulomatosis, have expressed renal failure at the time of diagnosis, and need hemodialysis, which later can be stopped in most of them.

Along with the kidneys and lungs with microscopic polyangiitis affects the gastrointestinal tract and peripheral nervous system. The nature of their lesion is the same as in Wegener's granulomatosis.

Diagnostics of the microscopic polyangiitis

Patients with microscopic polyangiitis show increased ESR, moderate hypochromic anemia, increasing in the case of pulmonary hemorrhage, neutrophilic leukocytosis, an increase in the concentration of C-reactive protein.

In contrast to nodular polyarteritis, HBV markers are absent in most patients. Almost 80% of patients in the blood are found to have ANCA, mainly to myeloperoxidase (p-ANCA), but 30% have c-ANCA.

[20], [21], [22], [23], [24]

Differential diagnosis

Microscopic polyangiitis is diagnosed on the basis of a clinical picture, morphological and laboratory data. However, almost 20% of patients do not have ANCA in their blood, and a kidney biopsy is not always possible. In these cases, the combination of rapidly progressing glomerulonephritis with other symptoms of vasculitis of small vessels allows one to suspect necrotizing vasculitis.

Since the treatment of microscopic polyangiitis and Wegener's granulomatosis is the same in the presence of severe viscerites determining the prognosis, there is no need for a clear delineation of these forms of systemic vasculitis.

Differential diagnosis of microscopic polyangiitis is also performed with nodular polyarteritis. In this case, the doctor should be guided by the clinical and laboratory features of both diseases. Nodular polyarteritis is characterized by abdominal pain syndrome and polyneuropathy, severe, sometimes malignant, arterial hypertension, which practically does not occur in patients with microscopic polyangiitis, lean urinary syndrome, aneurysm or stenosis of vessels during angiography, frequent infection with HBV. With microscopic polyangiitis, a combination of hemorrhagic alveolitis with rapidly progressive glomerulonephritis, ANCA in serum is more often detected.

In renal and pulmonary syndrome patients with microscopic polyangiitis need differential diagnosis with a number of diseases characterized by similar clinical symptoms.

Treatment of the microscopic polyangiitis

Treatment of microscopic polyangiitis as a form of ANCA-associated vasculitis is the combination of glucocorticoids with cytostatics. Principles and regimens of immunosuppressive treatment are similar to those used for the treatment of Wegener's granulomatosis.

In the treatment of low-immune fast-progressive glomerulonephritis within the framework of microscopic polyangiitis, a shorter course of treatment with cyclophosphamide may be used to induce remission followed by azathioprine therapy as maintenance therapy, although hemorrhagic alveolitis combined with rapidly progressive glomerulonephritis is not used. Severe pulmonary vasculitis within the microscopic polyangiitis serves as an indication for repeated courses of plasmapheresis and intravenous immunoglobulin. Another indication for the appointment of immunoglobulin is considered resistance to active immunosuppressive therapy, which is understood as the lack of effect (continued progression of vasculitis) after 6 weeks or more of glucocorticoids and cytotoxic drugs.

Forecast

The prognosis for microscopic polyangiitis, as well as for Wegener's granulomatosis, is determined by the damage to the lungs and kidneys. Prognostically unfavorable factor in relation to overall survival of patients is hemoptysis. The level of creatinine in the blood, before treatment exceeds 150 μmol / l, is a risk factor for the development of chronic renal failure. Taking into account the frequency of development of massive pulmonary hemorrhage, which is the main cause of death of patients with microscopic polyangiitis, even with the combined use of glucocorticoids and cytostatics, the 5-year survival rate is 65%. Along with pulmonary hemorrhage in an acute period, the lethal outcome often comes from infectious complications.

[25], [26]