A case of IgG4-related disease of the thymus

We report a rare case of IgG4-related disease of the thymus. A 77-year-old man was referred to our hospital because of a mass in the anterior mediastinum detected by thoracic CT. Enhanced CT showed a 53×33-mm mass in the left anterior mediastinum. The tumor in the left thymus had invaded the left phrenic nerve and pleura, and was initially suspected to be a thymoma. We performed extended thymo-thymectomy and lymph node dissection, with excision of the infiltrating surrounding tissues including the left phrenic nerve and pleura. Laryngeal nerve paralysis and chylothorax occurred after the operation. Histological examination revealed that the tumor consisted mainly of IgG4-positive plasma cells, with elevation of the serum IgG4 level. These findings suggested that the tumor was IgG4-related disease of the thymus.