Microscopic Polyangiitis

Diagnosis

Indications for Testing

  • Multiorgan system involvement in patient

Laboratory Testing

  • Nonspecific testing
    • BUN/creatinine – usually normal unless significant renal involvement
    • CBC – mild anemia; rule out infectious process
    • Urinalysis – hematuria, proteinuria, granular or red cell casts
    • Erythrocyte sedimentation rate/C-reactive protein – elevated >50% of the time
    • ANCA – antimyeloperoxidase predominant
      • Most effective test to demonstrate vasculitis
      • Positive in 50-75% of patients
  • Antiglomerular basement membrane antibodies – small number (5-10%) positive; use to rule out Goodpasture syndrome

Histology

  • Gold standard for diagnosis
  • Small and mid-size artery, venule, and capillary necrotizing vasculitis (no granulomas visualized)
  • Renal biopsy – focal segmental necrotizing, glomerulonephritis with crescents (identical to biopsy in Wegener granulomatosis and Churg-Strauss syndrome)

Imaging Studies

  • Chest x-ray – bilateral, patchy opacities suggest hemorrhage
  • CT – ground glass attenuation; eventual honeycombing when fibrosis occurs

Differential Diagnosis

Clinical Background

Microscopic polyangiitis (MPA) is a necrotizing vasculitis of the small vessels without granulomatous inflammation.

Epidemiology

Pathophysiology

  • Necrotizing vasculitis of the microscopic vessels (small arteries, arterioles, capillaries or venules) in sites other than kidney
  • Necrotizing crescenteric glomerulonephritis on renal biopsy

Clinical Presentation

  • Constitutional – weight loss, fever, myalgias
  • Otorhinolaryngological – oral ulcers, epistaxis, sinusitis
  • Renal – rapidly progressing glomerulonephritis
  • Cardiovascular – pericarditis, endocarditis
  • Neurological – mononeuritis multiplex, sensorimotor polyneuropathy
  • Dermatological – palpable purpura, papules, ulcers
  • Ophthalmological – scleritis, uveitis, episcleritis
  • Pulmonary – hemoptysis, chest pain (pleuritis), dyspnea, cough
  • Gastrointestinal – abdominal pain

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Urea Nitrogen, Serum or Plasma 0020023
Method: Quantitative Spectrophotometry

Test for elevated renal function

   
Creatinine, Serum or Plasma 0020025
Method: Quantitative Enzymatic

Test for elevated renal function

   
CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

May help in ruling out other diseases (infectious process)

   
Urinalysis, Complete 0020350
Method: Reflectance Spectrophotometry/Microscopy

Use in assessing renal involvement

   
Sedimentation Rate, Westergren (ESR) 0040325
Method: Visual Identification

Initial screen in vasculitis

   
Anti-Neutrophil Cytoplasmic Antibody with Reflex to Titer and MPO/PR-3 Antibodies 2002068
Method: Semi-Quantitative Indirect Fluorescent Antibody/Semi-Quantitative Multiplex Bead Assay

Most effective test to aid in classification of vasculitis

Components include anti-neutrophil cytoplasmic antibody, IgG; myeloperoxidase antibody; and serine proteinase 3 antibody

If screen is positive, titer and MPO/PR-3 antibodies testing will be added to aid in antibody determination

   
Renal Pathology Special Studies

Confirm type of vessel involvement or confirm renal glomerulonephritis

May not demonstrate disease due to skip lesions

 
Glomerular Basement Membrane Antibody, IgG by Multiplex Bead Assay and IFA 2008403
Method: Semi-Quantitative Multiplex Bead Assay/Qualitative Indirect Fluorescent Antibody

Rule out Goodpasture syndrome

   
Additional Tests Available
 
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
Anti-Neutrophil Cytoplasmic Antibody, IgG 0050811
Method: Semi-Quantitative Indirect Fluorescent Antibody

If ANCA screen detects antibodies ≥1:20 dilution, titer to end point is added

Myeloperoxidase Antibody 0050526
Method: Semi-Quantitative Multiplex Bead Assay