Polyarteritis nodosa (PAN) is a systemic vasculitis of medium-sized vessels that most commonly affects the skin, peripheral nerves, muscles, joints, gastrointestinal tract, and kidneys, but usually spares the lungs. Most cases are idiopathic, but PAN is associated with certain viral infections, most commonly hepatitis B virus (HBV) infection. Patients typically present with constitutional symptoms (e.g., fever, weight loss, muscle and joint pain); additional symptoms vary based on the organ of involvement (e.g., acute kidney injury, myocardial infarction, rash). ANCAs and cryoglobulins are typically negative on laboratory studies. The diagnosis is confirmed via biopsy or visceral angiography of the affected organs. Management typically involves immunosuppressive agents (e.g., glucocorticoids). For patients with HBV-associated PAN, antiviral therapy and, in selected cases, plasmapheresis, are also indicated.
- Systemic vasculitis of medium-sized vessels and small muscular arteries, leading to tissue ischemia 
- Most commonly involves the skin, peripheral nerves, muscles, joints, gastrointestinal tract, and kidneys
- Most cases are idiopathic. 
- Viral infections 
- Hepatitis B (incidence has ↓ from 30% to 7% due to vaccination)
- Less frequently: other viruses ; (e.g., hepatitis C, HIV, CMV)
- Nonspecific symptoms
- Renal involvement (∼ 60%): hypertension, renal impairment 
- Coronary artery involvement (∼ 35%); ↑ risk of myocardial infarction
- Skin involvement (∼ 40%): rash, ulcerations, nodules
- Neurological involvement: polyneuropathy (mononeuritis multiplex), stroke
- GI involvement: abdominal pain, melena, nausea, vomiting
- Usually spares the lungs
In PAN, the Pulmonary Artery is Not involved, PANmural inflammation of the arterial wall is present, and PAN may be associated with hePAtitis B.
PAN should be considered in adults < 65 years of age presenting with stroke or myocardial infarction.
General principles 
- PAN may involve various organs; no symptom is pathognomonic for PAN.
- The absence of lung involvement and glomerulonephritis helps differentiate PAN from other systemic necrotizing vasculitides (e.g., ANCA-associated vasculitis).
- Laboratory studies further support the diagnosis and help determine the underlying etiology.
- A biopsy or visceral angiography is required to confirm the diagnosis.
Laboratory studies 
- Inflammatory markers
- BMP: ↑ creatinine if there is renal involvement
- Hepatitis B, hepatitis C 
- Negative ANCA and cryoglobulins 
- Urinalysis: mild-moderate proteinuria and/or hematuria if there is renal involvement
Imaging studies 
Visceral angiography of affected organs
- Indications: Consider if biopsy is not possible.
Findings: most commonly seen in the renal, mesenteric, and hepatic artery branches (pulmonary arteries are usually not affected)
- Numerous microaneurysms (1–5 mm in diameter)
- Stenosis of small muscular arteries and medium-sized vessels
CTA or MRA
- Indications: assessment of disease extension, progression, and response to treatment
- Visceral hemorrhage or necrosis
- Large aneurysms, stenosis, and/or occlusion of the main renal artery and its branches
Biopsy of affected tissue 
- Indications: patients with accessible affected tissue (e.g., muscle; , skin, sural nerve) 
- Transmural inflammation ; with leukocytic infiltration and fibrinoid necrosis
- Inflammatory lesions in various stages of development and regeneration
Most guideline recommendations are based on low-level evidence or expert opinion. Use shared decision-making. 
- Consult rheumatology and/or other specialties as required.
- Immunosuppressants (e.g., glucocorticoids; PLUS cyclophosphamide) are indicated for all patients to achieve remission.
- Antiviral therapy; is indicated for HBV-associated PAN.
- Patients with nerve and/or muscle involvement often benefit from physical therapy.
Plasmapheresis may be considered for patients with life-threatening PAN refractory to pharmacotherapy and those with HBV-associated PAN. 
Initial therapy: Start remission induction therapy for patients with active disease.
- Severe disease : e.g., IV methylprednisolone pulses PLUS cyclophosphamide (first line) 
- Nonsevere disease: e.g., high-dose oral prednisone PLUS either azathioprine OR methotrexate
- Maintenance of remission: glucocorticoids PLUS a glucocorticoid-sparing agent (e.g., methotrexate or azathioprine) 
- Sustained remission: Therapy may be discontinued.
Some patients achieve remission with glucocorticoid monotherapy, however, the addition of glucocorticoid-sparing agents reduces the dose of glucocorticoids required, reducing the potential adverse effects. 
HBV-associated PAN 
- Consult a hepatologist for all patients; see “Treatment” in “Hepatitis B.”
- All patients require a 2-week course of high-dose glucocorticoids before antiviral therapy.
- Plasmapheresis may be considered.
The addition of plasmapheresis increases the rate of remission induction in patients with HBV-associated PAN.