Polyarteritis nodosa revisited: a review of historical approaches, subphenotypes and a research agenda.

Polyarteritis nodosa (PAN) is a rare form of primary systemic vasculitis with heterogeneous presentations, treatments and disease course. Historical approaches to classification and diagnostic terminology are reviewed. Since differentiation of PAN from microscopic polyangiitis (MPA) and other ANCA vasculitides by the Chapel Hill conference statements, and with hepatitis associated PAN defined as a secondary vasculitis, the phenotyping and subclassification of PAN has received little attention. Monogenic disorders similar to PAN have been described (familial Mediterranean fever, Adenosine Deaminase-2 deficiency), and cutaneous PAN and single organ vasculitis, discussed. The overlapping phenotypes between PAN and other primary vasculitic syndromes and subphenotypes within PAN are explored. This work will underpin development of newer treatment regimens and future genetic and related aetiologic studies.