Polyarteritis nodosa (ORPHA:767)
A rare, clinically heterogeneous, systemic disease characterized by necrotizing inflammatory lesions affecting medium-sized blood vessels. It most commonly affects skin, joints, peripheral nerves and the gastrointestinal tract.
Epidemiology
Prevalence of polyarteritis nodosa (PAN) has been estimated at 1/33,000 in France, Norway and Sweden. Changes in classification of systemic vasculitis and more precise delineation of these disorders make it difficult to determine exact epidemiological data.
Clinical description
PAN is defined as vasculitis affecting medium-sized vessels and has no pathognomonic clinical or laboratory features. There is a very broad range of clinical presentations depending on the underlying cause and age of onset, with different presenting features, courses, therapeutic implications, and prognoses. The most frequent form of the disease is a potentially life-threatening, idiopathic condition affecting mainly adults, and has a presentation with fever, fatigue, weight loss, myalgia and arthralgia, often with multisystem involvement (systemic PAN). In this form, cutaneous manifestations are common at onset. A limited form with subcutaneous nodules, indurated erythema, and livedo reticularis, and mild extracutaneous features has also been described, with no significant internal organ involvement (cutaneous PAN). Rare limited forms affecting the peripheral nerves, testicles, ureter, breasts, or ovaries have also been described and are known as single-organ PAN.
Etiology
The disease can be primary (primary PAN) or secondary, e.g. related to viral infection such as hepatitis B virus (secondary PAN).
Diagnostic methods
Diagnosis is based on the clinical features but often requires tissue biopsy showing necrotizing medium-sized vessel vasculitis, and/or angiography showing microaneurysms. Laboratory findings are non-specific and PAN is never associated with anti-neutrophil cytoplasm antibodies (ANCA).
Differential diagnosis
The main differential diagnoses are other medium-sized vessel vasculitides such as Kawasaki disease and also small-sized vessel necrotizing vasculitides, mainly microscopic polyangiitis.
Management and treatment
The main factors guiding treatment are the extent of organ involvement and disease progression. Glucocorticoids combined with 6 to 9 intravenous cyclophosphamide injections are prescribed to treat systemic PAN with factors of poor prognosis, as defined by the Five Factor Score (FFS). Milder cases (FFS=0) can be treated with glucocorticoids alone. Once remission is obtained, maintenance treatment with azathioprine is given for one year. When PAN is caused by HBV infection, treatment involves a combination of anti-viral drugs and plasma exchanges. Corticosteroids and immunosuppressants are not recommended because they stimulate viral replication and favor the development of liver cirrhosis.
Prognosis
Limited forms tend to have a favorable prognosis. Factors of poor prognosis are GI involvement, renal insufficiency, cardiac manifestations and central nervous system involvement. Causes of death include uncontrolled vasculitis and infections, as well as renal, gastrointestinal and cardiovascular manifestations.

                            Last update: 
                            October 2020


                            - Expert reviewer(s): 
                            Dr Xavier PUECHAL  - Pr Benjamin TERRIER