[A case of isoniazid (INH)-induced pneumonitis]

A 58-year-old man was referred for the evaluation of a lung nodule on chest X-ray. On admission, chest X-ray showed a solitary nodule with cavitation in the left lung field. Histological examination revealed epithelioid cell granulomas and the diagnosis of pulmonary tuberculosis was made. He was treated with INH, ethambutol (EB), and rifampicin (RFP). On the 16th day of treatment, he developed dry cough and high fever. On the 20th day, dyspnea developed and PaO2 was decreased to 38.2 Torr. Chest X-ray showed new widespread infiltrates in both lung fields and bilateral pleural effusions. The size of the cavitary lesion was decreased. Transbronchial biopsy specimen showed slight interstitial thickening, lymphocyte infiltration, and multiple granulomas. Drug lymphocyte stimulation test was positive only with INH (230%). INH-induced pneumonitis was highly suspected. All drugs was discontinued and hydrocortisone 2400 mg daily was started. He soon became afebrile, and dyspnea and dry cough resolved. Chest X-ray film showed resolution of infiltrative shadows. He was subsequently successfully treated with streptomycin, EB, and RFP without any adverse effects. To our knowledge, this is the sixth reported case of INH-induced pneumonitis.