Microscopic Polyangiitis

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

Vasculitis
- Churg-Strauss syndrome
- Polyarteritis nodosa
- Wegener granulomatosis
- Cryoglobulinemia
- Connective tissue disease
Autoimmune disease
- Systemic lupus erythematosus
- Mixed connective tissue disease
- Goodpasture syndrome
- Endocarditis
Glomerulonephritis
- Goodpasture syndrome
- Crescenteric glomerulonephritis
- Endocarditis
- Acute nephritis
- Post-streptococcal glomerulonephritis
Pulmonary – renal hemorrhage
- Wegener granulomatosis
- Goodpasture syndrome
- Systemic lupus erythematosus

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

Epidemiology

Incidence – 16-25/1,000,000 for systemic vasculitis as a group (includes Churg-Strauss, MPA, polyarteritis nodosa and Wegener granulomatosis)
Age – peak onset is 50-60 years
Sex – M>F, 1.8:1
Ethnicity – higher prevalence in Europeans (Southern >Northern descent)

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

Tests generally appear in the order most useful for common clinical situations

Test name: Urea Nitrogen, Serum or Plasma

ARUP #: 0020023

Methodology: Quantitative Spectrophotometry

Use:

Test for elevated renal function

Test name: Creatinine, Serum or Plasma

ARUP #: 0020025

Methodology: Quantitative Enzymatic

Use:

Test for elevated renal function

Test name: CBC with Platelet Count & Automated Differential

ARUP #: 0040003

Methodology: Automated Cell Count with Flow Cell Differential

Use:

May help in ruling out other diseases (infectious process)

Test name: Urinalysis, Complete

ARUP #: 0020350

Methodology: Reflective Photometry/Microscopic by Yellow IRIS

Use:

Use in assessing renal involvement

Test name: Sedimentation Rate, Westergren (ESR)

ARUP #: 0040325

Methodology: Westergren

Use:

Initial screen in vasculitis

Test name: Anti-Neutrophil Cytoplasmic Antibody with Reflex to Titer and MPO/PR-3 Antibodies

ARUP #: 2002068

Methodology: Semi-Quantitative Indirect Fluorescent Antibody/Semi-Quantitative Multi-Analyte Fluorescent Detection

Use:

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

Test name: Renal Pathology Special Studies

ARUP #:

Methodology:

Use:

Confirm type of vessel involvement or confirm renal glomerulonephritis

Limitations:

May not demonstrate disease due to skip lesions

Test name: Glomerular Basement Membrane Antibody Panel

ARUP #: 0051001

Methodology: Semi-Quantitative Multi-Analyte Fluorescent Detection/Qualitative Indirect Fluorescent Antibody

Use:

Rule out Goodpasture syndrome

Additional Tests Available

Test name: Anti-Neutrophil Cytoplasmic Antibody, IgG

ARUP #: 0050811

Methodology: Semi-Quantitative Indirect Fluorescent Antibody

Comments:

Test name: Myeloperoxidase Antibody

ARUP #: 0050526

Methodology: Semi-Quantitative Multi-Analyte Fluorescent Detection

Comments:

General

Tebo, Anne E., PhD. Assistant Medical Director, Immunology at ARUP Laboratories; Assistant Professor of Pathology (Clinical), University of Utah

Comprehensive Review: November 2011
Last Update: November 2011

Connective Tissue Diseases

Mixed Connective Tissue Disease

Polyarteritis Nodosa

Streptococcal Disease, Group A

Systemic Lupus Erythematosus

Vasculitis

Wegener Granulomatosis