Polyarteritis nodosa

Polyarteritis nodosa is a systemic inflammatory necrotizing vasculitis that involves small to medium-sized arteries (larger than arterioles). 

Epidemiology

Polyarteritis nodosa is more common in males and typically presents around the 5^th to 7^th decades. 20-30% of patients are hepatitis B antigen positive.

Associations

• hepatitis B

• hepatitis C

Clinical presentation

Patients can present with systemic and/or focal symptoms.

• systemic signs and symptoms are almost always present and are non-specific, including fever, malaise and weight loss

• localized symptoms relate to ischemia and infarction of affected tissues and organs; the most commonly involved vessels are the renal arteries ¹ while the pulmonary circulation is typically spared

Frequent sites of involvement are ^3,5,6:

• renal: 80-90%, tends to be the prominent site and major cause of morbidity (e.g. chronic kidney disease, hypertension, hemorrhage) and death

• cardiac: ~70%

• gastrointestinal tract: 50-70%

• hepatic: 50-60%

• spleen: 45%

• pancreas: 25-35%  

• CNS: 20-45% ⁴

Pathology

Initially, there is transmural and necrotizing inflammation of medium-sized arteries, mostly involving part of the circumference which causes weakening of the wall leading to microaneurysm formation and subsequent focal rupture. There is a predilection for branch points. Fibrinoid necrosis of vessels promotes thrombosis of vessels followed by infarction of the tissue supplied. Fibrous thickening and mononuclear infiltration occur at a later stage. Different stages of inflammation can occur in the same vessel at different points.

Radiographic features

CT

Routine contrast-enhanced CT may be entirely normal or may demonstrate focal regions of infarction or hemorrhage in affected organs. 

Angiography (DSA / CT angiography)

Direct catheter angiography is far more sensitive to changes within small vessels, although a good quality CTA can also demonstrate changes. Findings include:

• multiple microaneurysms

  • characteristic but not pathognomonic

  • typically 2-3 mm in size but can be up to 1 cm

  • in the kidneys, the microaneurysms typically involve the interlobar and arcuate arteries

• hemorrhage may be present due to focal rupture

• occlusion may be present

Treatment and prognosis

Polyarteritis nodosa is usually fatal if untreated, often as a result of progressive renal failure or gastrointestinal complications. Prompt treatment with corticosteroids and/or cyclophosphamide may result in remission, and a remission/cure can be achieved in 90% of patients ³. 

History and etymology

It was initially described by Kussmaul and Maier in 1866.

Differential diagnosis

• consider other vasculitides such as

  • microscopic polyangiitis: has a much more established association with ANCA and tends to affect smaller arterioles, capillaries and venules

  • rheumatoid vasculitis

  • systemic lupus erythematosus (SLE)

  • Churg-Strauss syndrome