[Carbamazepine-induced pneumonitis definitively diagnosed by accidental readministration]

An 82-year-old man had been treated by carbamazepine for convulsions. A month later he felt febrile and malaise. Laboratory data revealed liver dysfunction, hypoxemia, and chest radiograph and computed tomography (CT) of the thorax showed ground glass opacity in both lungs and mediastinal lymphadenopathy. Analysis of bronchoalveolar lavage fluid revealed pulmonary lymphocytosis. Drug-induced lymphocyte stimulation test (DLST) for carbamazepine using peripheral blood lymphocytes was negative. We gave him a possible diagnosis of carbamazepine-induced liver damage and pneumonitis. After stopping carbamazepine, we initiated corticosteroid therapy and he recovered well. One year later he again suffered from convulsions and was treated with carbamazepine in another hospital. A week later he became febrile and suffered appetite loss, and came to our hospital. His chest radiograph and CT again showed ground glass opacity and pleural effusion in both lungs. Along with the laboratory data we established a definitive diagnosis of carbamazepine-induced pneumonitis. We discuss the mechanism of carbamazepine-induced pneumonitis in which the DLST results were negative and the challenge test was positive.