S8C15P2-1: In this example of Henoch-Schonlein purpura, the epidermis shows slight hyperplasia of the basal unit (mild psoriasiform pattern) and hyperkeratosis. The papillary dermis is widened and edematous (pale). There are perivascular infiltrates of inflammatory cells in the upper portion of the reticular dermis. The infiltrates extend from the perivascular spaces into the interstitium of the upper portion of the reticular dermis. They are not prominent along vessels of the papillary dermis and are not collected at the dermal-epidermal interface. This is a fairly classic pattern of a leukocytoclastic angiitis in which epidermal involvement is minimal; the infiltrates are relatively confined to the perivenular spaces and to neighboring interstitial tissue in the upper portion of the reticular dermis. The inflammatory infiltrates are rich in neutrophils. If the infiltrates in the perivascular spaces and the interstitial tissue of the reticular dermis had been composed of lymphocytes and histiocytes, it would seem appropriate to classify the lesion as a lymphohistiocytic vasculitis, but this is not an accepted, or even favored, practice (Henoch-Schonlein purpura).

S8C15P2-2: This a classic pattern of leukocytoclastic angiitis, occurring in the setting of Henoch-Schonlein purpura. The perivascular infiltrates are composed mostly of neutrophils  and histiocytes. There are a few collections of extravasated red blood cells in the adventitia of the vessel. The wall of the vessel is intact, but there are fibrin deposits near the bottom of the field at the interface between the adventitia of the vessel and the reticular dermis. The fibrinoid necrosis is perivascular, not mural. Scattered neutrophils and fragments of nuclear debris are present in the condensed fibrin and in the neighboring interstitium of the reticular dermis. The scattered fragments of nuclear debris are a marker for leukocytoclasia, but both histiocytes and neutrophils can contribute.

S8C15P2-3: A renal biopsy from this patient with Henoch-Schonlein purpura shows focal mesangial sclerosis with shrinkage of the affected tuft (red arrows). Blue arrows point to an organizing “crescent” (focal sclerosing glomerulonephritis).

S8C15P2-4: In this example, the sclerosis is more centrally located. An organizing crescent is present to the left of the area of mesangial sclerosis.