Giant reactions to tuberculin in lepromatous leprosy patients.

A detailed account and definition is given of the previously inadequately described "giant reactions" to tuberculin occasionally seen in leprosy patients. The reaction is an accelerated and exaggerated response to species-specific antigens of Mycobacterium tuberculosis found in both PPD and New tuberculin. Our studies were performed in Malaysia, Uganda, Spain, and England. There was a significantly higher incidence of the phenomenon in Malaysia than in the other centers, but this may have been because there alone previously untreated lepromatous (LL and BL) patients were serially tested for up to three years after starting chemotherapy. Of the 28 patients exhibiting giant reactions, 27 occurred among lepromatous patients (24 LL and 3 BL), of which only 3 (1 LL and 2 BL) were untreated. One treated BL patient had developed, and one untreated BL patient was a family contact of, active tuberculosis. Giant reactions are uncommon in untreated and in very long-term treated LL patients, but may occur in up to a fifth of those receiving their first 1-3 years of chemotherapy. Although the mechanism is not yet understood, it appears to be a coincidence of delayed hypersensitivity of the tuberculin type and a less-delayed phenomenon of excessive local edema associated with local lymphadenopathy and short-lasting symptoms of malaise and pyrexia. It is suggested that the majority of giant reactions occur during a period of temporary lack of immune regulation associated with changing levels of antigenic load.