• Comparison of the prednisone treatment alone to thymectomy (ETTX) plus prednisone treatment, based on the clinical response to therapy measured over the 3 year trial period by the Area Under the Quantitative Myasthenia Gravis Weakness Score [ Time Frame: 3 years ] [ Designated as safety issue: Yes ]
  
• Testing the difference of total prednisone used over the 3 year trial period measured by pill count from blister packs (Area Under the prednisone Dose Time Curve, AUDTC) conditional on the results of comparing AUQMG. [ Time Frame: 3 years ] [ Designated as safety issue: Yes ]
  

Myasthenia gravis (MG) is an autoimmune disease involving the thymus in which 85 percent of patients have antibodies to muscle acetylcholine receptors (AchR-Ab) that interfere with neuromuscular transmission. MG frequently causes severe disability that can be life-threatening. Thymectomy—a surgical procedure that removes thymus gland tissue from the chest cavity—has been an established therapy for non-thymomatous MG, or MG without thymoma, for more than 60 years (based on retrospective, non-randomized studies). Corticosteroids are now being used increasingly either as the sole treatment or in combination with thymectomy. Both therapies have associated adverse effects and indications for their use based on randomized trial data are lacking.

The purpose of this 5-year trial is to determine if the surgical procedure, extended transsternal thymectomy (ETTX), combined with prednisone therapy is more beneficial in treating individuals with non-thymomatous MG than prednisone therapy alone. More specifically, this study will determine 1) if ETTX combined with prednisone results in a greater improvement in myasthenic weakness, compared to prednisone alone; 2) if ETTX combined with prednisone results in a lower total dose of prednisone, thus decreasing the likelihood of concurrent and long-term toxic effects, compared to prednisone alone; and 3) if ETTX combined with prednisone enhances quality of life by reducing adverse events and symptoms associated with the therapies, compared to prednisone alone.

Learning that thymectomy results in a meaningful reduction of prednisone dosage or even full withdrawal or reduces side effects related to prednisone would support using the two treatments—thymectomy and prednisone—together. However, if no meaningful reduction of prednisone dosage or side effects is shown, the results would mean that using the two treatments together offers no advantages over prednisone treatment alone.

After an initial screening, study participants will be randomized either to undergo the surgical procedure ETTX and receive prednisone treatment, or to receive prednisone treatment alone without surgery. Participants will be followed for at least 3 years.