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First Randomized Trial Shows Thymectomy Is Associated with Improved Clinical Outcomes for Myasthenia Gravis
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Thursday, August 11, 2016
Thymectomy combined with prednisone improved clinical outcomes in patients with nonthymomatous myasthenia gravis over a three-year period compared to prednisone alone, according to a new study published August 11 in the New England Journal of Medicine.
The randomized, controlled, multicenter trial is the first of its kind to assess the benefit of thymectomy versus medical treatment alone for myasthenia gravis, an autoimmune neuromuscular disease that can cause muscle weakness, vision problems, and other symptoms.
Thymectomy has been used to treat nonthymomatous myasthenia gravis — a form of the disease that does not include a thymoma, or chest tumor — for 75 years, the study's authors noted, but observational and retrospective studies were limited and have not shown a clinical benefit to surgery versus medical therapy alone. Because the neurologic disease is so rare, it was challenging to enroll enough patients to conduct a randomized, controlled study to ascertain the benefit of the surgery and identify "the clinical characteristics of the patients who should be offered the procedure," the study's authors added.
Previous nonrandomized studies had bias problems, said Gil I. Wolfe, MD, FAAN, Irvin and Rosemary Smith chair of the department of neurology at the Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo of the State University of New York and chief study author, in a press release accompanying the study. The new findings confirm that thymectomy is beneficial, the authors noted.
The researchers enrolled 126 patients who had myasthenia gravis for less than three years in the MGXT trial. The participants were randomized to receive alternate-day prednisone alone (n=60) or thymectomy plus alternate-day prednisone (n=66). The primary outcomes were a reduction in the Quantitative Myasthenia Gravis score – a 13-item, 39-point scale of muscle weakness, with higher scores indicating more severe weakness, and a reduction of 2.3 points signifying improved clinical status – and a significant reduction in prednisone dosage.
They found that patients in the thymectomy group had "significantly lower" Quantitative Myasthenia Gravis scores compared to patients in the prednisone group (a difference of 2.85 points, p<0.001) over the three-year study period. They also found that patients in the thymectomy group had lower prescribed dosages of prednisone (44 mg versus 60 mg in the prednisone-only group, p<0.001).
In addition, patients in the thymectomy group had fewer hospitalizations for exacerbations of myasthenia gravis (9 percent) than those in the prednisone-only group (37 percent, p<0.001). Among patients who were hospitalized, those in the thymectomy group had fewer cumulative days in the hospital (8.4±8.6 days) compared to those in the prednisone-only group (19.2±24.5 days; p=0.09). Compared to the prednisone-only group, patients in the thymectomy group had better scores on the Myasthenia Gravis Activities of Daily Living scale, an eight-question survey that assesses interference of myasthenia gravis symptoms with daily life.
The results, the study's authors wrote, provide evidence "supporting the use of thymectomy for improving clinical outcomes and reducing the need for immunosuppressive therapy" for patients with myasthenia gravis.
The study's authors noted several limitations, including the single-blind nature of the study and the pill-count method used to assess medical outcomes, which was "not a precise measure of actual intake."
In an accompanying editorial, Allan H. Ropper, MD, professor and executive vice chair of neurology at Harvard Medical School, noted that the results of the trial "reflect the difficulty in capturing these fluctuating and fatigable myasthenic symptoms." The clinical outcomes were better in the thymectomy group, he said, but the "absolute differences were moderate," and the main results were supported by secondary outcomes, showing that more patients in the thymectomy group had "minimal manifestations" by three years and a lower rate of need for immunosuppression with azathioprine.
While the findings "will be useful in counseling patients," he cautioned that they "offer no further clarity" for the selection of patients receiving thymectomy because secondary analyses did not show relative benefits based on gender or age. "Nevertheless, the appeal of a virtual cure by means of thymectomy is likely to persist because of the unappealing alternative of a long-term commitment to the use of glucocorticoids and immunosuppression," he said.