Microscopic polyangiitis M31.7

Rare, severe, p-ANCA- or c-ANCA positive (60% of patients), necrotizing, non granulomatous (differentiation from granulomatosis with polyangiitis =Wegener's granulomatosis) "small vessel" vasculitis (microscopic) as a (minus) variant of classic polyarteritis nodosa mostly without involvement of medium-sized or large arteries.

MPA is usually accompanied by necrotizing glomerulonephritis and pulmonary capillaritis. Often difficult to differentiate diagnostically from granulomatous vasculitides: Churg-Strauss syndrome/eosinophilia and granulomatosis with polyangiitis/combinationwith sino-nasal symptoms (= Wegener's granulomatosis).

The life-threatening pulmo-renal syndrome requires in most cases intensive care.

The incidence is 0.6-0.8/100,000 per year.

S.u. granulomatosis with polyangiitis

Prodromal stage with adynamia, subfebrile temperatures, night sweats and weight loss. 50% of patients develop rheumatic complaints (myalgias, arthralgias).

Kidneys:in the further course renal involvement is possible (80%) which can manifest as Rapid Progressive Glomerulonephritis.

Lung: pulmonary capillaritis (25%), hemoptysis, pleurisy, pneumonia.

Heart: cardiovascular system involvement.

Other: gastrointestinal tract and peripheral nervous system (polyneuritis) are possible.

Skin (40%/ the dermatologist is usually involved in this clinical picture only on a consultative basis). Symptoms are nonspecific, clinically difficult to delineate in individual cases because of the high variability of dermatologic symptoms. The symptoms should only be considered in the context of the known clinical diagnosis:

more common is a:

• Palpable purpura (is in the foreground of the dermatologic symptomatology)

less frequent are:

• Livedo
• persistent reticular erythema
• subcutaneous nodules and nodules
• Pyoderma gangraenosum-like(painful) ulcerations.

Positive (MPO-ANCA) p-ANCA in about 60% of pat. cANCAs may also be present in about 20% of patients.

High inflammatory parameters (ESR; CRP)

Note: pANCAs are not specific for MPA but are also found in other vaculitides.

A pronounced eosinophilia speaks against the disease.

Inconspicuous epidermis, extensive filling of the corium by dense, perivascularly accentuated infiltration of lymphocytic cells with numerous neutrophilic granulocytes and nuclear dust. Pronounced erythrocyte extravasation. Distinctly swollen vascular endothelia and pronounced fibrin deposits within the vessel walls. Leucocytoclastic vasculitis without immune complex deposits.

Leukocytoclastic vasculitis: small vessel vasculitis, no positive ANCA serology.

Drug and viral exanthema: no positive ANCA serology

Pyoderma gangraenosum: clinic, localized involvement, ulceration

Granulomatosis with polyangiitis (GPA) - histological evidence of granulomas

Eosinophilic granulomatosis with polyangiitis (EPGPA) - eosinophilic granulomatous infiltrates are the key feature.

In larger collectives with systemic vasculitides, the following breakdowns were shown: 66.7% with GPA, 17.0% with MPA, 16.3% with EGPA(Wójcik K et al. 2019).

5-year survival rate: approx. 70%; ANCA and CRP increases indicate a recurrence and a worsened prognosis.

The dermatological symptoms are extremely variable and not "'diagnosis-specific". Thus, the diagnosis can only be made by evaluating the histopathology in conjunction with the complex overall problem.

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