Comparative Clinical Features and Immune Responses After Extended Thymectomy for Myasthenia Gravis in Patients With Atrophic Versus Hyperplastic Thymus

Background. Although extended thymectomy is believed to be suitable for myasthenia gravis (MG) patients with hyperplastic thymus, it is not clear whether surgical treatment is indicated for MG patients with atrophic thymus. We therefore assessed the clinical features and immune responses in 175 MG patients who underwent thymectomy between 1990 and 2004. Methods. All patients underwent extended thymectomy by the transsternal approach. Clinical features, prognosis, and immune response after extended thymectomy were compared in patients with atrophic and hyperplastic thymuses. Results. Of the 175 patients, 47 had atrophic and 128 had hyperplastic thymuses. Although the median times to complete stable remission of the two groups were similar (4.9 versus 4.8 years; p = 0.513), the median time to clinical improvement was significantly longer in patients with atrophic thymus (3.3 versus 2.3 years; p = 0.005). Patients with atrophic thymus showed a greater increase in ectopic thymus in the anterior mediastinal adipose tissue. Elevated B-cell activating factor receptor, CD19, and CD21 were observed in both hyperplastic and atrophic thymuses, although serum immunoglobulin G concentration after thymectomy increased more in patients with atrophic than in those with hyperplastic thymus. Conclusions. Atrophic thymus may contribute to the progression of MG. Patients with MG who have a atrophic thymus show similar postoperative prognosis as those with hyperplastic thymus, suggesting that surgical therapy should also be considered for the former subset. (Ann Thorac Surg 2011; 91: 212-8) (C) 2011 by The Society of Thoracic Surgeons