Thymic Hyperplasia With Lymphoepithelial Sialadenitis-Like Features Arising in a Patient With Immunoglobulin G4-Related Disorders: A Case Report.

Thymic hyperplasia with lymphoepithelial sialadenitis-like features is characterized by thymic hyperplasia with lymphocytic infiltrates in the thymic epithelium. The lesion differs from other forms of thymic hyperplasia, including true and follicular thymic hyperplasia, in that it presents at an advanced age and has been reported to be unassociated with autoimmune diseases. We report a case of thymic hyperplasia with lymphoepithelial sialadenitis-like features in a 55-year-old male patient with a history of an immunoglobulin G4 (IgG4)-related disorder. Histologically, the resected mediastinal mass showed features consistent with those of thymic hyperplasia with lymphoepithelial sialadenitis-like features. In addition, the IgG4/IgG ratio was elevated in the polyclonal plasmacytoid infiltration. Thymic hyperplasia with lymphoepithelial sialadenitis-like features has not been reported to be associated with IgG4-related disorders; however, as shown in our report, it is crucial to include it in the differential diagnosis of a mediastinal mass in a patient with IgG4-related disorders.