Polyarteritis Nodosa & Microscopic Polyangiitis

Key Features

Essentials of Diagnosis

POLYARTERITIS NODOSA

• Medium-sized arteries are affected

• Clinical findings depend on the arteries involved; lungs are spared

• Common features

  • Fever

  • Abdominal pain

  • Extremity pain

  • Livedo reticularis

  • Mononeuritis multiplex

  • Anemia

  • Elevated acute phase reactants (erythrocyte sedimentation rate [ESR] or C-reactive protein or both)

• Kidney involvement causes renin-mediated hypertension

• Associated with hepatitis B (10% of cases)

MICROSCOPIC POLYANGIITIS

• Necrotizing vasculitis of small- and medium-sized arteries and veins

• Most common cause of pulmonary-renal syndrome: diffuse alveolar hemorrhage and glomerulonephritis

• Associated with antineutrophil cytoplasmic antibody (ANCA) in 75% of cases, usually anti-myeloperoxidase antibodies (MPO-ANCA) (that cause a P-ANCA pattern on immunofluorescence testing)

• ANCA directed against proteinase-3 (PR3-ANCA) (that cause a C-ANCA pattern on immunofluorescence testing) can also be observed

General Considerations

POLYARTERITIS NODOSA

• A necrotizing arteritis of medium-sized vessels that has a predilection for involving the skin, peripheral nerves, mesenteric vessels (including renal arteries), heart, and brain but spares the lungs

• Relatively rare, with a prevalence of about 30 cases per 1 million people

• Approximately 10% of cases are caused by hepatitis B; most cases of hepatitis B–associated disease occur within 6 months of onset of hepatitis B infection

MICROSCOPIC POLYANGIITIS

• A pauci-immune nongranulomatous necrotizing vasculitis that

  • Affects small blood vessels (capillaries, venules, or arterioles)

  • Often causes glomerulonephritis and pulmonary capillaritis

  • Often is associated with ANCA on immunofluorescence testing (directed against MPO, a constituent of neutrophil granules)

• Appears in a spectrum overlapping with both polyarteritis nodosa and granulomatosis with polyangiitis (formerly Wegener granulomatosis) because it

  • May involve medium-sized as well as small blood vessels

  • Tends to affect capillaries within the lungs and kidneys

• Rarely medications induce a systemic vasculitis associated with high titers of p-ANCA and features of microscopic polyangiitis, particularly

  • Propylthiouracil

  • Hydralazine

  • Allopurinol

  • Penicillamine

  • Minocycline

  • Sulfasalazine

Clinical Findings

Symptoms and Signs

POLYARTERITIS NODOSA

• Fever, malaise, weight loss, and other symptoms develop over weeks to months

• Pain in the extremities

• Vasculitic neuropathy

• Livedo racemosa, subcutaneous nodules, and skin ulcers reflect involvement of deeper, medium-sized blood vessels

• Digital gangrene is common

• Lower extremity ulcerations, usually occurring near the malleoli

• Renin-mediated hypertension due to involvement of renal arteries

• Acalculous cholecystitis or appendicitis caused by compromised function of major viscera

• Dramatic presentation in some cases

  • Acute abdomen caused by mesenteric vasculitis and gut perforation

  • Hypotension resulting from rupture of a microaneurysm in the liver, kidney, or bowel

• Subclinical cardiac involvement is common; overt cardiac dysfunction occurs occasionally

• Lungs are seldom (if ever) involved

MICROSCOPIC POLYANGIITIS

• "Palpable" (or "raised") purpura ...