The deoxyribonucleic acid (DNA) skin test in systemic lupus erythematosus. 2. Histological findings

A total of fifty-five biopsies from fifty-two intradermal DNA skin tests were studied. The biopsies were taken, 6, 8-10, 24 or 48 h after the injection of the DNA material. Necrosis of the vessel wall was taken to be the main characteristic of a specific reaction. In forty of the fifty-two tests the results of the histological evaluation closely matched the clinical results. In five of the fifteen cases with discrepancies, the histological evaluation ruled out clinically false positive test results. In three cases of SLE on corticosteroid treatment, the histological examination gave a positive result despite a clinically negative result. In seven of the fifteen cases the discrepancies occurred in borderline cases with reactions of 5 to 6 mm diameter. The amount of inflammatory cells in positive as well as in negative reactions was also recorded. The number of polymorphonuclear cells in positive reactions increased with the age of the reaction. The number of lymphocytes was not found to increase in the positive reactions, thus differing from the delayed hypersensitivity type of reactions. Rather, the reaction was characterized by an Arthus type of hypersensitivity. On the basis of the present study it may be concluded that clinically positive tests at 6 or 8 h may merely be expressions of nonspecific vascular alterations. On the other hand, in late reactions, even in patients on systemic treatment, histological examination revealed clinically negative results to be positive. By using the histological picture of hypersensitivity angiitis as the main diagnostic criterion the specificity of the clinical reactions may be established.