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microscopic polyangiitis

Term introduced in 1948 to describe disorder considered different from polyarteritis nodosa (PAN). Alias microscopic PAN. Epidemiology: (similar to PAN) 1) males affected more frequently than females 2) median age of onset is 50 years Pathology: 1) vulnerable organs include: a) kidneys (~80%) - pauci-immune necrotizing glomerulonephritis b) joints (~70%) c) skin (~50%) d) gastrointestinal tract (~40%) - GI bleed e) lungs (~20%) - alveolar hemorrhage - pulmonary infiltrates - pulmonary fibrosis f) peripheral nerves (~20%) 2) shares some features with Wegener's granulomatosis & polyarteritis nodosa (PAN) 3) distinguishing features from Wegener's granulomatosis: - involves skin in ~50% of patients [3] 4) distinguishing features from PAN: a) few or no immune complexes (pauci-immune) b) disease affects small vessels 1] capillaries 2] venules 3] arterioles c) glomerulonephritis 1] rapidly progressing 2] focal & segmental 3] necrotizing without granulomatosis d) inflammation of the pulmonary capillaries e) pulmonary alveolar hemorrhage (12-30%) Clinical manifestations: 1) characteristically affects lungs & kidneys [4] a) hemoptysis [4] b) pauci-immune necrotizing glomerulonephritis [4] 2) hypertension 3) weight loss 4) arthralgias, myalgias 5) peripheral neuropathy - mononeuritis multiplex - distal symmetric polyneuropathy 6) CNS: - pachymeningitis, cerebral hemorrhage, ischemic stroke 7) epididymitis 8) skin - subcutaneous nodules, necrotic ulcers, palpable purpura, livedo reticularis 9) abdominal pain, GI bleeding 10) sinusitis 11) sensorineural hearing loss Laboratory: 1) p-ANCA (MPO Ab) is positive in 75% (similar to PAN) [4] 2) c-ANCA (proteinase-3 Ab) may be positive 3) urinalysis a) active urine sediment b) proteinuria 4) azotemia 5) anemia 6) complement levels are normal 7) erythrocyte sedimentation rate (ESR) commonly > 100 mm/hr 8) renal biopsy not angiography best for diagnosis 9) open lung biopsy if no renal manifestations - transbronchial lung biopsy generally does not provide sufficient tissue for diagnosis [4] 10) skin biopsy 11) see ARUP consult [5] Radiology: - chest X-ray: pulmonary infiltrates [4] Diagnosis: - diagnostic considerations are similar to PAN Differential diagnosis: - Wegener's granulomatosis characterized by cANCA - microscopic polyangiitis involves skin in ~50% of patients [3] - polyarteritis nodosa (PAN) - see Pathology: for distinguishing features from PAN Management: 1) induction therapy (initial treatment) a) combination therapy b) rituximab 375 mg/m2/week (4 doses) in combination with glucocorticoids preferred induction for severe disease [8] c) methotrexate in combination with glucocorticoid preferred induction for less severe disease [8] d) prednisone + cyclophosphamide to induce remission - treatment for 3-6 months 2) maintenance therapy with methotrexate or azathioprine [4] - rituximab in combination with glucocorticoids if cyclophosphamide is contraindicated, not tolerated, or is otherwise unacceptable (NICE) [NGC] - mycophenolate acceptable for maintenance therapy - azathiaprine acceptable for maintenance therapy [4] 3) plasmapheresis may delay need for dialysis [4] 4) management considerations are similar to PAN

Interactions

disease interactions

Related

classic polyarteritis nodosa (PAN)

General

ANCA-associated vasculitis chronic vascular disease (chronic vasculopathy)

References

  1. Harrison's Principles of Internal Medicine, 14th ed. Fauci et al (eds), McGraw-Hill Inc. NY, 1998, pg 1912-14
  2. Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 610, 785
  3. Khasnis A and Langford CA. Update on vasculitis. J Allergy Clin Immunol 2009 Jun; 123:1226. PMID: 19501230
  4. Medical Knowledge Self Assessment Program (MKSAP) 14, 15, 16, 17, 18, 19. American College of Physicians, Philadelphia 2006, 2009, 2012, 2015, 2018, 2022. - Medical Knowledge Self Assessment Program (MKSAP) 19 Board Basics. An Enhancement to MKSAP19. American College of Physicians, Philadelphia 2022
  5. ARUP Consult: Microscopic Polyangiitis The Physician's Guide to Laboratory Test Selection & Interpretation https://www.arupconsult.com/content/microscopic-polyangiitis
  6. Ramsey J, Amari M, Kantrow SP. Pulmonary vasculitis: clinical presentation, differential diagnosis, and management. Curr Rheumatol Rep. 2010 Dec;12(6):420-8 PMID: 20882372
  7. Kallenberg CG. The diagnosis and classification of microscopic polyangiitis. J Autoimmun. 2014 Feb-Mar;48-49:90-3. Review. PMID: 24461388
  8. Chung SA, Langford CA, Maz M et al. 2021 American College of Rheumatology/Vasculitis Foundation guideline for the management of antineutrophil cytoplasmic antibody-associated vasculitis. Arthritis Rheumatol 2021 Aug; 73:1366-1383. PMID: 34235894 https://onlinelibrary.wiley.com/doi/10.1002/art.41773