Microscopic Polyangiitis - MPA

  • Diagnosis
  • Algorithms
  • Background
  • Lab Tests
  • References
  • Related Topics

Indications for Testing

  • Unexplained systemic illness with multiple system involvement (renal, neurologic, dermatologic)

Laboratory Testing

  • Nonspecific testing – helpful in excluding other diagnoses or identifying organ dysfunction
    • BUN/creatinine – usually normal unless significant renal involvement
    • CBC – mild anemia; rule out infectious process
    • Urinalysis – hematuria, proteinuria, granular or red cell casts
    • C-reactive protein (CRP)
    • ANCA – antimyeloperoxidase predominant
      • Most effective test to demonstrate vasculitis
      • Positive in at least 40% of patients
        • Absence does not rule out MPA
  • Antiglomerular basement membrane antibodies – 5-10% of MPA patients are positive for this
    • Most useful to rule out antiglomerular basement membrane disease (anti-GBM disease)

Histology

  • Small and mid-size artery, venule, and capillary necrotizing vasculitis (nongranulomatous)
  • Pulmonary disease is often capillaritis – absence of immune complex deposition
  • Renal biopsy – focal segmental necrotizing, glomerulonephritis with crescents
    • Identical to biopsy in granulomatosis with polyangiitis and eosinophilic granulomatosis with polyangiitis

Imaging Studies

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

Differential Diagnosis

Microscopic polyangiitis (MPA) is a necrotizing vasculitis without granulomatous inflammation. MPA is considered a small vessel ANCA-associated vasculitis (Chapel Hill 2012).

Epidemiology

Pathophysiology

  • Necrotizing vasculitis of the microscopic vessels (predominantly arterioles, capillaries or venules) in sites other than kidney
  • Necrotizing crescentic glomerulonephritis on renal biopsy
  • Differentiated from granulomatosis with polyangiitis (GPA) by absence of granulomatous inflammation

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 – pulmonary hemorrhage, dyspnea, cough, chest pain
    • Pulmonary hemorrhage may be life threatening
  • Gastrointestinal – abdominal pain
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.

Urea Nitrogen, Serum or Plasma 0020023
Method: Quantitative Spectrophotometry

Creatinine, Serum or Plasma 0020025
Method: Quantitative Enzymatic

Limitations 

Assay interference (negative) may be observed when high concentrations of N-acetylcysteine (NAC) are present

Negative interference has also been reported with NAPQI (an acetaminophen metabolite) but only when concentrations are at or above those expected during acetaminophen overdose

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

Urinalysis, Complete 0020350
Method: Reflectance Spectrophotometry/Microscopy

C-Reactive Protein 0050180
Method: Quantitative Immunoturbidimetry

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

Renal Pathology Special Studies

Limitations 

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

Follow-up 

Positive result should be confirmed by renal biopsy

Guidelines

American Society for Clinical Pathology. Choosing Wisely - Five Things Physicians and Patients Should Question. An initiative of the ABIM Foundation. [Last revision Feb 2015; Accessed: Jan 2016]

Jennette JC, Falk RJ, Bacon PA, Basu N, Cid MC, Ferrario F, Flores-Suarez LF, Gross WL, Guillevin L, Hagen EC, Hoffman GS, Jayne DR, Kallenberg CG M, Lamprecht P, Langford CA, Luqmani RA, Mahr AD, Matteson EL, Merkel PA, Ozen S, Pusey CD, Rasmussen N, Rees AJ, Scott DG I, Specks U, Stone JH, Takahashi K, Watts RA. 2012 revised International Chapel Hill Consensus Conference Nomenclature of Vasculitides. Arthritis Rheum. 2013; 65(1): 1-11. PubMed

General References

Chung SA, Seo P. Microscopic polyangiitis. Rheum Dis Clin North Am. 2010; 36(3): 545-58. PubMed

Falk RJ, Nachman PH, Hogan SL, Jennette JC. ANCA glomerulonephritis and vasculitis: a Chapel Hill perspective. Semin Nephrol. 2000; 20(3): 233-43. PubMed

Jayne D. Challenges in the management of microscopic polyangiitis: past, present and future. Curr Opin Rheumatol. 2008; 20(1): 3-9. PubMed

Kawakami T. New algorithm (KAWAKAMI algorithm) to diagnose primary cutaneous vasculitis. J Dermatol. 2010; 37(2): 113-24. PubMed

Merkel PA, Seo P, Aries P, Neogi T, Villa-Forte A, Boers M, Cuthbertson D, Felson DT, Hellmich B, Hoffman GS, Jayne DR, Kallenberg CG M, Krischer J, Mahr A, Matteson EL, Specks U, Luqmani R, Stone J, Vasculitis Clinical Research Consortium, OMERACT 7 Special Interest Group. Current status of outcome measures in vasculitis: focus on Wegener's granulomatosis and microscopic polyangiitis. Report from OMERACT 7. J Rheumatol. 2005; 32(12): 2488-95. PubMed

Mukhtyar C, Flossmann O, Hellmich B, Bacon P, Cid M, Cohen-Tervaert JW, Gross WL, Guillevin L, Jayne D, Mahr A, Merkel PA, Raspe H, Scott D, Witter J, Yazici H, Luqmani RA, European Vasculitis Study Group (EUVAS). Outcomes from studies of antineutrophil cytoplasm antibody associated vasculitis: a systematic review by the European League Against Rheumatism systemic vasculitis task force. Ann Rheum Dis. 2008; 67(7): 1004-10. PubMed

Villiger PM, Guillevin L. Microscopic polyangiitis: Clinical presentation. Autoimmun Rev. 2010; 9(12): 812-9. PubMed

Medical Reviewers

Last Update: August 2016