[A case of isoniazid-induced pneumonitis]

A 55-year-old man was given a diagnosis of pulmonary tuberculosis. He was treated with isoniazid (INH), rifampicin (RFP), ethmbutol (EB) and pyrazinamide (PZA). After three weeks of treatment, he developed fever, dyspnea and dry cough. A chest X-ray taken at that time showed new reticulo-nodular shadows bilaterally and right pleural effusion. Ga scintigram showed strong uptake in both lungs. Transbronchial lung biopsy revealed alveolitis, suggesting drug-induced pneumonitis. Drug lymphocyte stimulation tests for INH, RFP, EB and PZA were negative. Because his symptoms were severe, all drugs were discontinued and daily predonisolone (30 mg) therapy was started. The symptoms and bilateral reticulo-nodular shadows soon resolved. The antituberculosis drugs were changed to streptomycin and levofloxacin, but these were ineffective. Therefore, EB, RFP and PZA, which only rarely induce pneumonitis, were carefully restarted in that order. Pneumonitis did not recur and the pulmonary tuberculosis improved. This clinical course suggests INH-induced pneumonitis.