Microscopic polyarteritis (MPA)

Abstract

In the nineteenth century, following Kussmaul and Maier’s [1] classic description, periarteritis nodosa was considered as a rare distinct disease entity. It was characterized by visible nodular lesions at autopsy involving the muscular arteries. Capillaries and venules were never involved. However, in the twentieth century, cases were described in which the diagnosis was made at microscopy — with consequent changes in the emphasis of disease descriptions. This led to an evolving concept of vasculitis and its classification. Initially, al.l the new descriptions were lumped together in an expanding unity. Subsequently, one entity after another was split off into distinct separate forms (Figure 10.1). Vesz-premi and Jancso [2] were the first to describe a case with microscopic involvement of vessels in the absence of any gross evidence of periarteritis nodosa. This was felt at the time to be a most unusual case, and a decade later only five cases had been described with microscopic disease in the absence of gross lesions [3]. The chief impetus for the expanding interest in the microscopic forms of necrotizing vasculitis in the first half of the twentieth century (and for including them in the same category as classic PAN) was the recognition of the vascular manifestations of al.lergies. This could occur in relationship to classic al.lergens, such as foreign proteins, to bacteria, and to drugs.