Microscopic polyangiitis M31.7

Rare, severe, p-ANCA- or c-ANCA positive (60% of patients), necrotizing "small vessel" vasculitis (microscopic) as (minus) variant of the classic polyarteritis nodosa mostly without infestation of medium or large arteries.

MPA is usually accompanied by necrotizing glomerulonephritis and pulmonary capillaritis. Diagnosis is often difficult to distinguish from Churg-Strauss syndrome and granulomatosis with polyangiitis (= Wegener's granulomatosis).

The life-threatening pulmo-renal full picture usually requires intensive treatment.

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 (myalgia, arthralgia).
• Kidneys:in the further course of the disease renal extinction possible (80%) which can manifest itself as Rapid Progressive Glomerulonephritis.
• Lungs: pulmonary capillaritis (25%), haemoptysis, pleuritides, pneumonia.
• Heart: cardiovascular system involvement
• Other: Gastrointestinal tract and peripheral nervous system (polyneuritis) are possible.
• skin (40%; the dermatologist is usually only involved in consultation with the patient in this clinical picture):
  • Clinically difficult to define in individual cases due to the high variability of dermatological symptoms:
    • Palpable purpura (is in the foreground of the dermatological symptoms)
    • more rarely:
      • Livedo
      • urticarial exanthema
      • subcutaneous nodules and nodes
      • Pyoderma gangraenosum-like ulcerations.

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

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

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.

Leucocytoclastic vasculitis: vasculitis of small vessels, no positive ANCA serology

Drug and virus exanthema: no positive ANCA serology

Pyoderma gangraenosum: Clinic, localized infestation, ulcer

Granulomatosis with polyangiitis (GPA) - histological detection of granulomas

Eosinophilic granulomatosis with polyangiitis (EPGPA)- pioneering eosinophilic infiltrates

Microscopic polyangiitis (MPA)- no histological evidence of granulomas

In larger collectives with systemic vasculitis the following distributions were found: 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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10. Wójcik K et al (2019) Clinical characteristics of Polish patients with ANCA-associatedvasculitides-retrospective
    analysis of POLVAS registry. Clin Rheumatol doi: 10.1007/s10067-019-04538-w.