29th January 2024

Polyarteritis nodosa (PAN)

Background

Epidemiology

Polyarteritis nodosa can occur at any age, with the peak incidence being 45-65 years of age. There is a male predominance of 2:1. 

Aetiology

The cause is largely unknown (idiopathic); however, some cases are associated with active hepatitis B. 

Pathophysiology 

Necrotising vasculitis of medium-sized vessels leads to microaneurysm formation, especially at the bifurcations of vessels. This can cause end-organ damage by aneurysmal rupture and thrombosis of the vessel. PAN most commonly affects the skin, peripheral nerves, muscles, joints, gastrointestinal tract and kidneys. 

Clinical features 

Non-specific symptoms such as fever, weight loss and malaise, along with muscle and joint pains, may develop sub-acutely over weeks or months. PAN may affect every organ of the body with a predisposition for the skin, kidneys, nerves and gastrointestinal tract. 

Renal involvement occurs in around 60% of patients, which can present with hypertension and impaired renal function. Skin involvement occurs in 40%, mainly on the legs and can be very painful. Common findings include purpura, livedo reticularis, ulcers, nodules or gangrene. Neurological involvement includes polyneuropathy (mononeuritis multiplex) along with central nervous system presentations such as seizures and stroke. Gastrointestinal involvement can cause abdominal pain, malaena, nausea and vomiting. More serious complications can occur, such as bowel infarction and perforation. Coronary artery involvement occurs in 35% with an increased risk of myocardial infarction. 

Diagnosis

Blood tests such as raised ESR, anaemia, leukocytosis and a negative ANCA screen are important for the diagnosis of this condition. Hepatitis serology needs to be carried out in all patients, given the association with active hepatitis B infections. Urine analysis can show proteinuria and haematuria. 

If there is skin, muscle or nerve involvement, a biopsy of the tissue will greatly aid in diagnosis. Muscle biopsy can demonstrate transmural inflammation of the arterial wall with leukocytic infiltration and fibrinoid necrosis. Angiography commonly demonstrates numerous small aneurysms and stenosis of small and medium-sized vessels of the involved organs, most commonly seen in the renal arteries. 

Treatment

PAN is fatal within weeks to months without treatment as a result of kidney, heart or gastrointestinal complications. Immunomodulation with glucocorticoids is used initially. Immunosuppressive therapies such as cyclophosphamide can also be added to therapy. Antiviral therapy may be required if the patient is positive for hepatitis B. PAN does not relapse following completed treatments. 

References

• About vasculitis, Vasculitis UK. Available at: https://www.vasculitis.org.uk/about-vasculitis [Accessed 28th January 2022].
• Bessant, R., Borms, J., Ford, C., 2020.Medicine for MRCP. Oxford Specialty Training 
• Polyarteritis Nodosa, Johns Hopkins Vasculitis Center. Available at: https://www.hopkinsvasculitis.org/?s=polyarteritis [Accessed 16th January 2022]
• Vasculitides, Amboss. Available at: https://www.amboss.com/us/knowledge/Vasculitides/ [Accessed 17th January 2022].https://www.amboss.com/us/knowledge/Vasculitides/