A case of IgG4-related interstitial lung disease showing usual interstitial pneumonia pattern: Unusual case for histological features with pathological proof

The case was a 71-years-old male with chest abnormal shadow and persistent dry cough. Chest CT showed ground-glass opacities, traction bronchiectasis, and honeycomb-like change in the bilateral lower lobes. Laboratory tests revealed high serum IgG4 concentration. Pathological examination of the video-assisted thoracoscopic surgery biopsy taken from the right lung showed a pattern compatible with usual interstitial pneumonia (UIP) with strong infiltration of IgG4-positive plasma cells. Based on these findings, diagnosis of IgG4-related interstitial lung disease (ILD) was made. One year later, when ILD was progressed with the appearance of swelling of both submandibular glands, treatment with prednisolone (PSL) was started. When the dose of PSL was tapered to 7.5 mg, left pleural effusion emerged in chest CT. Further examination yielded the diagnosis of lung adenocarcinoma and he was treated with chemotherapy. After two cycles of chemotherapy, IgG4-related interstitial lung disease exacerbated, thus he was re-treated with moderate dose of PSL. Response to PSL treatment was good, but unfortunately, chemotherapy for lung cancer was discontinued due to the risk for re-exacerbation of ILD. To our knowledge, this is the eighth case of IgG4-related ILD ever reported and the second case diagnosed as UIP pattern pathologically.