A Case Report of IgG4-Related Disease Clinically Mimicking Pleural Mesothelioma
A 74-year-old male patient had been followed-up for 4 years after radical prostatectomy due to adenocarcinoma of prostate. He was experienced smoker with 30 pack-years and had history of medication for diabetes mellitus and hypertension, but no history of drug, allergy or autoimmune disease and occupational or environmental exposure to asbestos. On the follow-up examinations, the right pleural effusion on chest X-ray (, one year ago) and the patchy lesions of the right lung on computed tomography (, 6 months ago) were found. However, serum prostate-specific antigen level was within normal limit, and repeated cytological evaluations for pleural effusion showed no evidence of malignancy. Multiple nodules and diffuse pleural thickening in the left lower lung field were newly developed 3 months ago (). Positron emission tomography also disclosed hot uptake on these new nodules (, arrows) and no identifiable lesions on the other organs including pancreas, thyroid and salivary gland. Under the impression of mesothelioma, wedge resection was done. Microscopically, visceral pleura and alveolar interstitium were thickened with dense cellular infiltration and fibrosis (). Infiltrates were mainly composed of lymphoplasma cells without cytological atypia (). Many multinucleated giant cells of foreign-body type were noted near the degenerated elastic layer of the visceral pleura on the inflammatory and fibrotic background (). Some blood vessels showed angiocentric infiltration of lymphoplasma cells, but there was no evidence of destructive changes such as neutrophilic infiltration and fibrinoid necrosis in the vessel walls (). All special stains for acid fast bacilli, Grocott-Gomori methenamine silver, periodic acid-Schiff, and mucicarmine failed to demonstrate any organism. The results of immunohistochemical stain with IgG (1:1,000, Dako, Glostrup, Denmark) and IgG4 (1:2,000, Binding Site, Bermingham, UK) revealed increased proportion of IgG4-positive plasma cells, estimated at about 40% (). Based on the histological and immunohistochemical findings, IgG4-related disease was confirmed, and increased serum level of IgG4 (over than 201 mg/dL) were subsequently checked. The patient showed excellent response to treatment with steroid (prednisolone) and followed-up over 20 months without any evidence of recurrence.