Polyarteritis nodosa

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

Epidemiology

Polyarteritis nodosa (PAN) is commoner in males and typically presents around the 5^th to 7^th decades.  Twenty to thirty percent of patients are hepatitis B antigen positive.

Clinical presentation

Patients can present with systemic and focal symptoms. 

Non specific systemic  signs and symptoms are almost always present and include fever, malaise and weight loss. 

Localised symptoms relate to ischaemia and infarction of affected tissues and organs. The most commonly involved vessels, are the renal arteries ¹, with visceral involvement also considered relatively common. The pulmonary circulation is typically spared, although bronchial arteries may occasionally be involved.

Frequent sites of involvement are ^3,5:

• renal: 80-90%, tends to be the prominent site and major cause of death
• cardiac: ~70%
• gastrointestinal tract: 50-70%
• hepatic: 50-60%
• spleen: 45%
• pancreas: 25-35%  
• CNS complications: 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 . 

Markers

• pANCA: levels can correlate with disease activity

Radiographic features

CT

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

Angiography/CT angiography (CTA)

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

• multiple microaneurysms
  • characteristic but not pathognomonic
  • typically  2-3 mm in size but can be up to 1cm
  • in the kidneys, the micro aneurysms typically involve the inter lobar and arcuate arteries
• haemorrhage may be evident due to focal rupture
• occlusion may also be evident

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 cyclophosphamide can results in remission, and a remission or cure able to be obtained in 90% of patients ³. 

History and etymology

It was initially described by Kassmaul and Maier in 1866

Differential diagnosis

• consider other vasculitides such as
  • microscopic polyangitiis: 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