Erythema Component of the Tuberculin Reaction.

THE development of erythema is often a striking feature of the reaction to tuberculin. It occurs in the cutaneous test of Von Pirquet, and its development was the criterion of positivity in the conjunctival test of Wolff-Eisner and Calmette. It is usually well developed in the test which superseded both of these, the intracutaneous test of Mantoux. Over the years, however, particularly with the extensive use of the Mantoux test for survey purposes, the significance of the erythema component of the reaction has been seriously questioned. Its development has been largely abandoned as the index of a positive reaction, and the idea has as a result become widespread that the development of erythema is a non-specific response to the irritant effect of tuberculin which is quite unrelated to the presence of true tuberculin sensitivity. I do not propose to question, or even to discuss, the validity of the criteria at present used for defining a positive tuberculin reaction. I hope, however, to be able to show that erythema is as much a characteristic part of the tuberculin reaction as is induration and that the erythema component exhibits some interesting, and possibly important, properties of its own. The observations are based on testing almost 2oo young service men, just over half of whom were suffering from active tuberculosis. They were tested with old tuberculin by conventional techniques beginning with i T.U., followed 48 hours later (if induration of 6 mm. diameter failed to develop) by io T.U., and again 48 hours later, if the reaction was negative, by IOO T.U. The pattern of development of erythema in positive tuberculin reactions can be divided into several groups which are illustrated in Fig. I. The thick lines show the course of induration. The lower edge of the curve shows the average diameter, and the thickness of the line the depth of induration. In the commonest kind of reaction the diameter of induration reaches its maximum around 48 hours and then falls to a slightly smaller value which is often maintained 40-