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ABOUT THE MGTX STUDY

Funding Agency : National Institute of Neurological Disorders and Stroke

Abstract: Myasthenia gravis (MG) is an autoimmune disease involving the thymus in which 85% of patients have antibodies to muscle acetylcholine receptors (AchR-Ab) that interfere with neuromuscular transmission and can cause severe, sometimes life-threatening, weakness.

Thymectomy has been used world-wide to treat non-thymomatous MG, based on retrospective non-randomized studies. Prednisone (a corticosteroid) is also frequently used to treat MG. Both therapies are often employed together and both have adverse effects. A recent evidence-based review of thymectomy in non-thymomatous MG patients concluded that the benefits of thymectomy had not been established because published studies had serious methodological flaws. They identified the need for a randomized controlled trial.

The present multicenter, multiracial, international, single-blinded, clinical study (MGTX) meets that need and is now actively recruiting patients. It aims to answer three questions: compared to prednisone alone, does ETTX combined with prednisone result in (1) a greater improvement in myasthenic weakness (2) a lower total dose of prednisone (3) an enhanced quality of life by reducing adverse events and symptoms associated with the therapies?

Non-thymomatous MG patients aged at least 18 but less than 60 years with generalized AchR-Ab positive non-thymomatous MG, disease duration less than 3 years, are randomized to receive extended transsternal thymectomy (ETTX) or no thymectomy. Both groups will receive prednisone administered by a 'blind' evaluator according to the same set protocol aimed at establishing the minimum dose needed to achieve and maintain Minimal Manifestation (MM) status. Patients may be receiving prednisone at entry but not other immunosuppressive medications. Each patient is seen at least every 3 months for 3 years.

The primary endpoint is a composite measuring (a) clinical efficacy of therapy evaluated by the QMG weakness score (b) the total dose of prednisone (Area under the Dose time Curve, AUDTC) (c) the frequency of treatment associated adverse events.

A significant difference favoring ETTX would establish its clinical benefits in this patient population, and provide indirect evidence of the possible benefits of ETTX in patients not receiving prednisone medication. Conversely, failure to demonstrate a significant difference in the global or individual components of the primary endpoint would suggest that thymectomy is an unnecessary procedure in the population studied. Subgroup analysis may show whether benefits are confined to those who are prednisone naive at entry or in a particular age group.

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