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Polyarteritis Nodosa

Background

Classic polyarteritis nodosa (PAN or c-PAN) is a systemic vasculitis characterized by necrotizing inflammatory lesions that affect medium-sized and small muscular arteries, preferentially at vessel bifurcations.
These lesions result in microaneurysm formation, aneurysmal rupture with hemorrhage, thrombosis, and, consequently, organ ischemia or infarction.

Kussmaul and Maier first described PAN in 1866. The autopsy of a patient with fever, weight loss, abdominal pain, and polyneuropathy revealed areas of focal inflammatory exudations that gave rise to palpable nodules along the course of medium-sized arteries.

PAN, like other vasculitides, affects multiple systems and has protean manifestations, although it most commonly affects skin (see the image below), joints, peripheral nerves, the gut, and the kidney.
The lungs are usually spared with PAN. A typical PAN patient might present with fever, night sweats, weight loss, skin ulcerations or tender nodules, and severe muscle and joint pains developing over weeks or months. (See Etiology, Presentation, and Workup.)

Nonspecific, firm, tender subcutaneous nodules wit

Nonspecific, firm, tender subcutaneous nodules without livedo reticularis and/or systemic involvement may be the first sign of polyarteritis nodosa (PAN).

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See Cutaneous Clues to Accurately Diagnosing Rheumatologic Disease, a Critical Images slideshow, to help recognize cutaneous manifestations of rheumatologic diseases. Also see the slideshow Vasculitis: Case Presentations for more information on clinical, histologic, and radiographic imaging findings in various forms of vasculitis. For information on pediatric PAN, see Childhood Polyarteritis Nodosa.

Insight into PAN requires some understanding of how this rare disease has been defined. Periarteritis nodosa was a term used from the mid-1800s to the 1900s to describe a spectrum of systemic vasculitic disorders, including diseases that manifested as arterial aneurysms, as well as those that caused diffuse necrotizing glomerulonephritis.
The term periarteritis nodosa was changed to polyarteritis nodosa in the mid-1900s to reflect the transmural inflammation of arteries caused by this disorder.

The understanding of vasculitides continued to increase by the 1980s with the discovery of antineutrophil cytoplasmic antibodies (ANCAs). Microscopic polyangiitis (MPA; formerly called microscopic polyarteritis) is an ANCA-associated systemic vasculitis that has some features similar to those of classic PAN, with the additional involvement of renal glomeruli and pulmonary capillaries.

Features of PAN

In 1990, the American College of Rheumatology (ACR) established criteria for research purposes in order to differentiate PAN from other forms of vasculitis.
A committee of ACR physicians selected 10 disease features of PAN; in order for PAN to be diagnosed, at least 3 of the 10 ACR criteria should be present when a radiographic or pathological diagnosis of vasculitis is made
(see Presentation and Workup):

Weight loss of 4 kg or more

Livedo reticularis

Testicular pain/tenderness

Myalgia or leg weakness/tenderness

Mononeuropathy or polyneuropathy

Diastolic blood pressure greater than 90 mm/Hg

Elevated blood urea nitrogen (BUN) or creatinine level unrelated to dehydration or obstruction

Presence of
hepatitis B surface antigen or antibody in serum

Arteriogram demonstrating aneurysms or occlusions of the visceral arteries

Presence of polymorphonuclear neutrophils in a biopsy specimen from a small- or medium-sized artery

The strong association of MPA with ANCA, as well as the pathologic and clinical differences between MPA and PAN, demonstrate that PAN and MPA are likely separate disorders. It was not until 1994 that histologic criteria to distinguish PAN from MPA were defined at the international Chapel Hill Consensus Conference (CHCC).
According to the CHCC criteria, the presence of vasculitis in arterioles, venules, and capillaries defines the diagnosis of MPA (although small- and medium-sized arteries may also be involved in MPA) and excludes the diagnosis of PAN. (See Presentation, DDx, and Workup.)

Stages

PAN is divided into subacute, acute, and chronic stages. In the subacute stage, infiltration of mononuclear cells becomes more prominent, while in the acute stage, polymorphonuclear neutrophils infiltrate all layers of the vessel wall. (See Etiology.)

In the chronic stage, fibrinoid necrosis of the vessels causes thrombosis and tissue infarction. Aneurysmal dilatations of the involved arteries, as large as 1 cm in size, are characteristic findings of PAN. Kidney lesions show predominant arteritis without glomerulonephritis; however, in patients with severe hypertension, glomerulosclerosis may be superimposed with glomerulonephritis. Pulmonary arteries are not involved, and bronchial artery involvement is uncommon.

Treatment

Corticosteroids are the cornerstone of treatment. Additional courses include the following:

Idiopathic PAN that is steroid refractory or includes major organ involvement: corticosteroids plus cyclophosphamide are the standard of care

Hepatitis B–related PAN: corticosteroids with antiviral agents (eg, vidarabine, interferon alpha-2b) and plasmapheresis

In patients with steroid-refractory and recurrent PAN, case reports describe response to treatment with biologic agents (eg, infliximab, etanercept, tocilizumab, tofacitinib, rituximab)

Severe PAN: plasma exchange has been used

See Treatment and Medication.

For patient education information, see What Is Polyarteritis Nodosa?.

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