Corticosteroids are considered the mainstay of treatment of IgG4-RD, and for many of its manifestations, response to therapy is favorable. The usual regimen consists of prednisolone or prednisone at a dose of between 30 mg/d and 1 mg/kg/d, but the optimal dose and duration of corticosteroid therapy remains to be defined. A number of other immunosuppressant drugs, such as azathioprine, mycophenolate mofetil, cyclophosphamide, and methotrexate, have also been used as corticosteroid-sparing agents. Additionally, successful treatment of IgG4-RD has been reported with bortezomib and rituximab. For treatment of IgG4-related fibrosing mediastinitis in particular, evidence for efficacy is anecdotal and based mainly on case reports. In three previous case reports of IgG4-related fibrosing mediastinitis, patients improved after steroid therapy, a noticeable event because mediastinal fibrosis is considered resistant to pharmacologic treatment. Specifically, two patients presented with symptoms from extrathoracic disease, whereas one patient complained of exertional dyspnea. In all patients, the size of mediastinal mass decreased after initiation of corticosteroids, and the patient with dyspnea showed remission of symptoms. A few other cases have been described in terms of retrospective analysis without information regarding treatment outcome.