Reply to Letter to Editor regarding the article, "Polyarteritis nodosa presenting as peripheral vascular disease and acute limb ischemia".

Thank you for your comment on oral and ocular involvement in vasculitis and the importance of careful physical examination. There has been confusion in the classification of primary systemic vasculitis and it still persists to an extent. The American College of Rheumatology Criteria 1990 for the classification of polyarteritis nodosa (PAN) do not differentiate it from microscopic polyangiitis (MPA).[1] The Chapel Hill Consensus Conference in 1994 defined the different types of primary systemic vasculitis. This was an attempt to formulate the most accepted nomenclature for vasculitis and to construct root definitions concentrating on the pathologic involvement of size and type of blood vessels. It restricted the definition of PAN to necrotizing vasculitis of medium and small arteries excluding glomerulonephritis and vasculitis in arterioles, capillaries, and venules.[2]

From 2004–2006, the European Medicines Agency made an attempt to formulate an algorithm to classify systemic vasculitis into Churg-Strauss syndrome > Wegener's granulomatosis (WG) > MPA > PAN based on the available classification criteria. Antineutrophil cytoplasmic antibody (ANCA) was included as a surrogate marker to classify systemic vasculitis. PAN diagnosis was possible as a last resort in the algorithm, i.e. only if the patient does not satisfy the criteria of the other three vasculitis and has histologic or angiographic evidence of medium-sized artery involvement. Any remaining patients were termed as unclassifiable.[3] In 2008, the French Vasculitis Study Group based on 262 patients of PAN and 687 patients of other vasculitis published certain positive and negative predictive criteria for the diagnosis of PAN. Ear, nose, and throat signs were included as a negative predictive variable for the classification of PAN.[4]

There has been an overuse of the term PAN in the past, the true incidence and prevalence of the disease is low. PAN presents as constitutional features of fever, myalgia, weight loss with raised acute-phase proteins, and an evidence of ischemia of single or multiple organ systems. Mononeuritis multiplex, acute abdomen with intestinal bleeding, spleen and kidney infarcts, and skin lesions are usual presenting symptoms. Ischemic orchitis is a classic feature described in the disease, but rarely seen. Peripheral ulcerative keratitis, scleritis, episcleritis, retinal vasculitis, and necrosis of tongue, palate, and salivary gland may be possible in the disease, but unusual, being common in ANCA-associated vasculitis, particularly granulomatous polyangiitis (WG). Medium-sized artery vasculitis limited to a single tissue, for example, leading to necrosis of the tongue is often termed as localized PAN.[5] The most common being cutaneous PAN. These terms confuse the terminology and represent disease processes separate from systemic necrotizing PAN.

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