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PAN (PolyArteritis Nodosa)
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.[6] 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 radiographic or pathological diagnosis of vasculitis is made[6] (see Presentationand 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
- Biopsy of small- or medium-sized artery containing polymorphonuclear neutrophils
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.)