eMedicine Specialties > Rheumatology > Vasculitis

Microscopic Polyangiitis: Differential Diagnoses & Workup

Author: Mehran Farid-Moayer, MD, Adjunct Clinical Faculty, Department of Psychiatry, Sleep Disorders Clinic, Stanford Medical Center
Contributor Information and Disclosures

Updated: Dec 6, 2006

Differential Diagnoses

Acute Mesenteric Ischemia
Infective Endocarditis
Churg-Strauss Syndrome
Leukocytoclastic Vasculitis
Cryoglobulinemia
Polyarteritis Nodosa
Glomerulonephritis, Crescentic
Wegener Granulomatosis

Other Problems to Be Considered

Acute nephritis
Vasculitis associated with collagen vascular disease

Workup

Laboratory Studies

  • Hematology laboratory studies
    • Leukocytosis
    • Anemia (normocytic anemia)
  • Elevated erythrocyte sedimentation rate (ESR)
  • Renal tests
    • Elevated serum BUN and creatinine (70%)
    • Abnormal urine sediment
    • Proteinuria (80%)
    • Hematuria (67%)
    • Leukocyturia (44%)
    • Erythrocyte casts
  • Antineutrophil cytoplasmic antibodies
    • ANCA positive (80%)
    • Perinuclear ANCA related to myeloperoxidase ANCA (60%)
    • Cytoplasmic ANCA related to proteinase-3 ANCA (40%)
  • Blood cultures to rule out bacterial endocarditis
  • Normal C3 and C4

Imaging Studies

  • Chest radiograph
    • Bilateral irregular, nodular, and patchy opacities
    • Pulmonary cavitary lesions (less frequently than Wegener granulomatosis)
    • Diffuse parenchymal infiltrates secondary to pulmonary alveolar capillaritis and hemorrhage
  • Other imaging studies – Indicated for the complications of the disease and specific organ system involvement, such as abdominal CT scan for pancreatitis or mesenteric angiography to differentiate from polyarteritis nodosa

Other Tests

  • Ordered according to the specific organ system involved
    • ECG indicated for myocardial infarction, pericarditis, and congestive heart failure
    • Gastrointestinal endoscopy in case of gastrointestinal bleeding
    • Electromyography (EMG) in case of clinical evidence of neuropathy

Procedures

  • Skin biopsy if skin is involved
  • Open lung biopsy
  • Renal biopsy to help diagnose crescentic glomerulonephritis
  • Sural nerve biopsy if EMG results are consistent with sural nerve involvement

Histologic Findings

Pathologically, microscopic polyangiitis (MPA) may cause necrotizing arteritis that is histologically identical to that caused by polyarteritis nodosa.

According to the Chapel Hill consensus conference on the classification of small vessel vasculitis, polyarteritis nodosa and MPA are distinguished pathologically by the absence of vasculitis in vessels other than arteries in patients with polyarteritis nodosa and the presence of vasculitis in vessels smaller than arteries, such as arterioles, venules, and capillaries, in patients with MPA.

Because of sparing of muscular and larger vessels in MPA, macroscopic infarcts similar to those seen in polyarteritis nodosa are uncommon. Histologically, segmental fibrinoid necrosis of the media may be present, but in some, the change is limited to infiltration with neutrophils, which become fragmented as they follow the vessel wall (leukocytoclasia). The term leukocytoclastic angiitis is given to such lesions, most commonly found in postcapillary venules.

Immunoglobulins and complement components may be present in the vascular lesions of the skin. The paucity of immunoglobulin is demonstrable using immunofluorescence microscopy (ie, pauci-immune injury).

The glomerulonephritis in MPA is characterized by focal necrosis, crescent formation, and the absence or paucity of immunoglobulin deposits. Pulmonary manifestation is in the form of pulmonary alveolar capillaritis. Biopsy of the muscle and sural nerve may reveal necrotizing vasculitis in small and medium vessels.

More on Microscopic Polyangiitis

Overview: Microscopic Polyangiitis
Differential Diagnoses & Workup: Microscopic Polyangiitis
Treatment & Medication: Microscopic Polyangiitis
Follow-up: Microscopic Polyangiitis
Multimedia: Microscopic Polyangiitis
References
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References

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Further Reading

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Keywords

microscopic polyangiitis, MPA, small vessel vasculitis, microscopic polyarteritis nodosa, microscopic PAN, small vessel vasculitides, systemic vasculitis, Wegener granulomatosis, Wegener's granulomatosis, Churg-Strauss syndrome, polyarteritis nodosa

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Contributor Information and Disclosures

Author

Mehran Farid-Moayer, MD, Adjunct Clinical Faculty, Department of Psychiatry, Sleep Disorders Clinic, Stanford Medical Center
Mehran Farid-Moayer, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians-American Society of Internal Medicine, American Medical Association, and American Thoracic Society
Disclosure: Nothing to disclose.

Medical Editor

Bryan L Martin, DO, Assistant Chief, CoFellowship Director, Department of Allergy-Immunology, Departments of Internal Medicine and Pediatrics, Walter Reed Army Medical Center; Assistant Professor, Uniformed Services University of the Health Sciences
Bryan L Martin, DO is a member of the following medical societies: American Academy of Allergy Asthma and Immunology, American College of Physicians, American Medical Association, American Osteopathic Association, and Texas Medical Association
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Elliot Goldberg, MD, Dean of the Western Pennsylvania Clinical Campus, Professor, Department of Medicine, Temple University School of Medicine
Elliot Goldberg, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians, and American College of Rheumatology
Disclosure: Nothing to disclose.

CME Editor

Alex J Mechaber, MD, FACP, Assistant Dean for Medical Curriculum, Associate Professor of Medicine, Division of General Internal Medicine, University of Miami Miller School of Medicine
Alex J Mechaber, MD, FACP is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians-American Society of Internal Medicine, and Society of General Internal Medicine
Disclosure: Nothing to disclose.

Chief Editor

Vecihi Batuman, MD, FACP, FASN, Professor of Medicine, Section of Nephrology-Hypertension, Tulane University School of Medicine; Chief, Medicine Service, Southeast Louisiana Veterans Health Care System
Vecihi Batuman, MD, FACP, FASN is a member of the following medical societies: American College of Physicians, American Society of Hypertension, American Society of Nephrology, and International Society of Nephrology
Disclosure: Nothing to disclose.

 
 
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