The tcrm" ReactionW has beell given to those cpisodes of significant inRammation occurring in leprosy which are the direct result of infection with Mycohacterium le-prae, and arc not due to secondary infection, trauma, etc. Many different types of reaction have been dcscribed, and the subject remained extremely confuscd throughout the first half of this century. However, since 1958 (: 1) it has increasingly been agreed that the majority fall into one or other of two groups, even though terminology remains controyersial (4. II. 14. 21).

The bctter defined group is commonly known as erythema nodosum leprosum (ENL)(: I. 7), although the Panel of Reaction of the 8th International Congress of Leprology recommended the term" Lepro_ matous Lepra Reaction"(.). Briefly, it consists of episodes of crops of painful, tender, erythema nodosum-like papules, which in severe cases may pustulate or necrose, which are often accompanied hy fever and malaise, and which may he complicated by neuritis, orchitis, lymphadenopathy, iridocyclitis, arthritis and proteinuria. ENL occurs only in lepromatous and small numbers of. borderline-lepromatous patients (ie, LL, LI and BL on the modified Ridley-Jopling spectrum classification (15. 111)). Although wen recognized before the introduction of sulfone treatment, it is particularly common in treated lepromatous leprosy, more than.'50 per cC'nt of such patients developing ENT, hy the end of the first year of treatment (:!:!). Histologically, on a backgrouncl usually of resolving lepromatous lC'prosy, the lesions~ nsist of vasculitis. polymorphonuclear 1Il6ltrate, hypcremia and fragmC'nted lepro-sy bacilli. The manifC'stations of ENT, may