HENOCH‐SCHÖNLEIN PURPURA

HENOCH-SCHONLEIN PURPURA (anaphylactoid purpura) presents with a characteristic rash, which is frequently associated with arthritis, gastro-Intestlnal and renal lesions and, rarely, other organ involvement. The initial diagnosis is often made by a dermatologist or a prediatrician. The underlying pathological process is a vasculitis which tends to affect the small blood-vessels, in contradistinction to polyarteritis nodosa, in which the medium-sized arteries are involved.' The retiology is idiopathic in most cases. In one reported series up to two-thirds of the !patients had suffered a prior respiratory tract Intectton," and in another series 14 out of 77 had a proven streptococcal infection.' Drugs and food allergens have occasionally been incriminated. The mechanism is thought to be a hypersensitivity reaction of the Arthus type. Immunofluorescence studies have shown antigen-antibody complexes deposited in both skin and kidneys.' The condition occurs more commonly in children than in adults. In adults, the sex ratios are approximately equal, but in children males are affected twice as often as females. Purpura is the most constant feature of the cutaneous lesions. In children this is usually preceded by erythematous maculas, by urticarial or papular lesions, or by a combination of these. In adults the purpura often arises as the initial sign." Cutaneous lesions tend to occur in crops, the most common sites being the legs, thighs, buttocks and arms. Blisters, ulceration and necrosis are rare in children, but occur not uncommonly in about 16% of adults.' The rash usually clears within six weeks, but recurrences are very common. In adults recurrences often arise over periods longer than 12 months afterwards.· Lever" describes the pathological changes in the skin as occurring in dermal arterioles, venules and capillaries. These vessels show swelling of endothelial cells, and deposition of fibrinoid material within and around the vessel wall. There is a perivascular cellular infiltrate predominantly of neutrophils with varying numbers of eostnophils, but only a few lymphocytes. Fragmentation of polymorph nuclei (leucocytoclasis) is seen in early lesions. Extravasation of red cells also occurs, and leads to deposition of hramcsidertn in lesions of longer standing. Localized cedema, which may be recurrent, is present in