[in Japanese]

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A 79-year-old man received steroid therapy at another hospital for immunoglobulin (Ig) G4-related sclerosing cholangitis. During follow-up at our department for suspected nontuberculous mycobacteriosis, we found a suspected obstruction in the lumen of the right lower lobe branch and a nodular shadow in the right lower lobe. Bronchoscopy revealed a tumor in the lumen, which raised suspicion of malignancy. Histopathological specimens showed no malignant findings, and IgG4-positive plasma cells were observed, but the IgG4/IgG-positive cell ratio was approximately 20%, which did not meet the diagnostic criteria for IgG4-related disease. The patient's imaging showed improvement of the mass and nodular shadows after increasing the steroid dosage, suggesting relapse of IgG4-related sclerosing cholangitis.

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