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Ann Thorac Surg 2007;84:360-361
© 2007 The Society of Thoracic Surgeons
Division of Cardiothoracic Surgery, Columbia University, New York–Presbyterian Hospital, 177 Fort Washington Ave, New York, NY 10032
(Email: alfred.jaretzki{at}snet.net).
We read with anticipation the comprehensive retrospective review [1] in which the long-term remission rates of this potentially important minimally invasive operation [2] have been meticulously collected using Kaplan-Meier analysis [3]. The authors’ have concluded that their results are comparable with those following transsternal procedures, that patients with less severe disease have higher complete remission (CR) rates, and that complete responses are durable.
Unfortunately the authors have not used what are now considered accepted standards of evaluation [4, 5], and most importantly they have developed a set of definitions of remission (CR) that raise questions concerning the authors’ conclusion that "the 5-year Kaplan-Meier CR rate is comparable with that obtained after transsternal procedures."
The authors’ definition of CR consists of two subgroups: "asymptomatic off all medications" and "asymptomatic on low-dose prednisone or azathioprine." These definitions contradict the "Recommendations for Clinical Research Standards" of the Medical/Scientific Advisory Board of the Myasthenia Gravis Foundation of America (MGFA) [4, 5], which were developed specifically to eliminate the multiple ad hoc definitions and classifications that were being widely used and that were making comparative analysis of results of therapy virtually impossible [6].
The MGFA "complete stable remission" status requires the patient be off all medication in addition to a "careful examination by someone skilled in the evaluation of neuromuscular disease" (not simply an asymptomatic status). Patients with a similar status, but still receiving myasthenia gravis (MG) medication (for whatever reason) are separately and appropriately defined as being in "pharmacological remission." Patients who have not reached either status are classified in the various subgroups of "minimal manifestations." Although we are in no way refuting the potential advantages of continuing low-dose immunosuppression after a patient has otherwise satisfied the criteria of remission, the author’s explanation that it has become the practice of their neurologists to continue these medications to avoid the potential of relapses does not justify defining these patients as being in complete remission.
With an understanding of the previously mentioned issues, the authors’ reported Kaplan-Meier CR rates at 3 and 6 years of 43% and 46%, respectively, for the entire 147-patient cohort and 44% and 46% for the earlier 84-patient cohort. In our view these rates are not valid complete remission rates since patients receiving immunosuppressive therapy are included. Therefore these determinations do not permit comparative analysis with valid remission rates reported by others.
Furthermore, the Kaplan-Meier CR rates of the "asymptomatic patients" off all medication, of 33% and 35% at 3 and 6 years, respectively, do not seem to compare favorably with either the combined transcervical-transsternal (T-4) resections [7] at 5 and 7.5 years of 50% and 81%, respectively, especially because the latter series had 80% moderately severe or severe MG manifestations. They also do not compare favorably with two Extended Transsternal T-3b resection series [8, 9], the first 5 and 6 years of 44% and 49%, respectively, and the second 5 and 7.5 years of 40% and 50%, respectively.
On the other hand, the authors’ data seem to confirm that patients with less severe disease have higher complete remission rates and that the responses are durable. However we take exception to: (1) the inclusion of thymomas in the authors’ series (8.3%) because there are a number of reasons to limit such an evaluation to patients with nonthymomatous MG; (2) the inclusion of crude data in the analysis, especially the use of uncorrected data and the use of patients "followed" in the denominator rather than patients "operated upon," because comparative analysis of this type of data is very misleading [6]; and (3) the use of one of the Osserman Clinical Classifications, especially because, in this series, the Clinical Classifications were apparently converted to the Osserman classification from MGFA Clinical Classification data obtained on review of the patient information.
Accordingly, as has been previously recommended [10] and as supported by Shrager and colleagues [1], the time has come for two or more surgical programs to prospectively compare thymectomy resectional techniques using well-controlled, well-monitored, and nonrandom Class II studies (American Academy of Neurology nomenclature). Frankly there are too many variables that can not be controlled and compared in retrospective studies to continue to compare the results of even well-designed retrospective studies.
Presently a large international, multicenter, randomized prospective study supported by the National Institutes of Health–National Institute of Neurological Disorders and Stroke and the MGFA is actively enrolling patients [11]. This study hopes to clarify the role of surgery in nonthymomatous MG by comparing the extended transsternal thymectomy to no thymectomy in patients receiving prednisone. We encourage enrollment in this study and look forward to subsequent cooperative studies investigating the relative merits of the various surgical techniques.
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  M. Lucchi, R. Ricciardi, F. Melfi, L. Duranti, F. Basolo, G. Palmiero, L. Murri, and A. Mussi Association of thymoma and myasthenia gravis: oncological and neurological results of the surgical treatment Eur. J. Cardiothorac. Surg., May 1, 2009; 35(5): 812 - 816. [Abstract] [Full Text] [PDF]
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 J. B. Shrager and L. R. Kaiser Reply. Ann. Thorac. Surg., July 1, 2007; 84(1): 361 - 361. [Full Text] [PDF]
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