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Ann Thorac Surg 2003;76:1-3
© 2003 The Society of Thoracic Surgeons
a Department of Surgery, Columbia Presbyterian Medical Center, New York, New York, USA
b Department of Neurology, Haukeland Hospital, University of Bergen, Bergen, Norway
c Department of Neurology, Case Western Reserve University, Cleveland, Ohio, USA
d Department of Neurology, University of Virginia, Charlottesville, Virginia, USA
e Duke University Medical Center, Durham, North Carolina, USA
* Address reprint requests to Dr Jaretzki, 21 Little Point St, PO Box 365, Essex, CT 06426-0365, USA.
e-mail: alfred.jaretzki{at}snet.net
It is generally believed that a total thymectomy is indicated when thymectomy is used to treat autoimmune nonthymomatous myasthenia gravis (MG) and the best available data, albeit retrospective, suggest that the more complete the resection the better the results (Fig 1) [1, 2]. However, there are no controlled prospective studies that determined unequivocally which thymectomy technique gives the best results, nor even that the entire thymus needs to be removed. In recent issues of this journal, there are two additional reports describing the results of two thymectomy techniques that are used in the treatment of MG.
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Pego-Fernandes and colleagues reported in two retrospective studies [4, 5] their combined experience with thymectomy using a partial sternotomy and removal of the entire thymus and surrounding fat in 478 patients with MG. The crude remission rate corrected for mean length of follow-up was 12.7% at 7.3 years. Corticosteroids were used in an unspecified number of patients. There were no deaths or nerve injuries. The authors stated that "the results are very similar to the literature data."
In the first study, the Kaplan-Meier remission rates, a desirable form of analysis, are impressive although not equal to those of the combined transcervical-transsternal thymectomy at 7.5 years (Fig 1). However, as is the problem with all the retrospective thymectomy studies, the patient cohorts are not the same and so might favor one or the other technique. In the second study, the reported corrected crude remission rate, although an unreliable measure, does not compare favorably with the 35% to 60% rate for the more aggressive resections [2]. In fact, it is lower than the basic transcervical thymectomy rate of Papatestas [6] and approximately the same as the reported rate of spontaneous remissions [7]. This marked variance suggests the existence of some major unrecognized unfavorable baseline characteristics in their patient cohort.
Those reports are illustrative of the MG thymectomy literature [1, 2] and demonstrate that attempts to conclude that one resectional technique is equal to or better than another by comparing retrospective studies, may be misleading. Among other factors, the patient populations, accompanying therapy, and details of evaluation are not the same. Furthermore, retrospective analyses do not address the extreme variability and unpredictability of MG, the differing response to treatment among patients with different subtypes of MG, or the variability in the selection of patients for thymectomy. The problems of analysis are compounded by a lack of common definitions of disease severity and response to therapy and a lack of objective preoperative and postoperative assessment criteria. In addition, when patients continue to take immunosuppressive medications after thymectomy, it is not possible to infer retrospectively what contribution to the ultimate result was made by the thymectomy per se [8].
Properly designed prospective studies are required to resolve the debate regarding the relative effectiveness of the various thymectomy resectional techniques. A prospective randomized clinical trial has been recommended to help resolve the role of thymectomy in any form in the treatment of MG [9], Class I evidence in the American Academy of Neurology (AAN) nomenclature [10]. At this time such a study comparing immunosuppression alone with immunosuppression plus the extended transsternal thymectomy is being developed [11]. However, it would be extremely difficult to develop a randomized study specifically comparing the various thymectomy resectional techniques, primarily because of surgeon resistance resulting in major recruitment problems; therefore, it is unlikely that such a study will be performed in the near future.
Accordingly, because properly performed nonrandomized studies have been shown to be valid [12, 13], we urge investigators to undertake nonrandomized prospective studies of two or more thymectomy techniques [14] (class II or class III evidence in the American Academy of Neurology nomenclature, depending on whether there is a control arm) [10]. The data bank concept should be employed in which two or more institutions would compare their techniques prospectively by using computer-based patient records. The assessment should be independent of the treating teams (Franklin G. Personal communication 2002; Co-Chair, Quality Standards Subcommittee, American Academy of Neurology). The use of clinical research standards, which include definitions of clinical classification, quantitative assessment of disease severity, grading systems of postintervention status, standardization of numeric grading for all significant variables, and approved methods of analysis is required [15–17]. A rigid auditing process must be in place to review all the clinical records and monitor the quality of the database, including validation for completeness and accuracy. Collaboration with experts in the field of biostatistics and outcomes analysis is mandatory in the design of the studies, collection of data, and evaluation of the results.
A 3- to 5-year follow-up evaluation will probably be required. The primary focus of comparative analysis should be complete, stable remission. Survival instruments, which are used in the analysis of remission, are the most reliable determinant [7]. Kaplan-Meier life-table analysis is the technique of choice [18, 19]. Levels of clinical improvement, although less definitive, can also be evaluated if performed quantitatively [16, 20]. The use of crude data, crude data corrected for length of follow up, and clinical classifications to compare results must not be employed. Exacerbations after remission, as well as hospital and long-term morbidity and mortality data, should be compared. Quality of life evaluation should also be considered because therapy for MG may not be innocuous and may not produce a completely stable remission. Although disease-specific quality of life instruments for MG are highly desirable in this evaluation [19], they are not available at this time. Quality of life evaluation, however, should not replace survival-remission analysis.
Although such studies require considerable attention to detail in their development and execution, they must be performed and must replace retrospective analyses. Funding should be made available. The importance of research in MG exceeds the disorder’s relative rarity because the financial burden to society and the compromise of individual quality of life is high. In addition, in this era of outcome analyses, these steps are not only desirable but are mandatory.
References
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  L. Yu, J. Li, S. Ma, J. Jiang, T. Wang, Z. Gamliel, Y. Jing, X. Zhang, and M. J. Krasna Different Characteristics of Nonthymomatous Generalized Myasthenia Gravis With and Without Oropharyngeal Involvement Ann. Thorac. Surg., November 1, 2007; 84(5): 1694 - 1698. [Abstract] [Full Text] [PDF]
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 T. Kotani, Y. Kotake, H. Morisaki, J. Takeda, H. Shimizu, T. Ueda, and A. Ishizaka Activation of a Neutrophil-Derived Inflammatory Response in the Airways During Cardiopulmonary Bypass Anesth. Analg., December 1, 2006; 103(6): 1394 - 1399. [Abstract] [Full Text] [PDF]
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J. B. Shrager, D. Nathan, C. J. Brinster, O. Yousuf, A. Spence, Z. Chen, and L. R. Kaiser Outcomes After 151 Extended Transcervical Thymectomies for Myasthenia Gravis Ann. Thorac. Surg., November 1, 2006; 82(5): 1863 - 1869. [Abstract] [Full Text] [PDF]
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V. Tomulescu, V. Ion, A. Kosa, O. Sgarbura, and I. Popescu Thoracoscopic thymectomy mid-term results. Ann. Thorac. Surg., September 1, 2006; 82(3): 1003 - 1007. [Abstract] [Full Text] [PDF]
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 H.-S. Hsu, C.-S. Huang, B.-S. Huang, H.-C. Lee, K.-P. Kao, W.-H. Hsu, and M.-H. Huang Thymoma is associated with relapse of symptoms after transsternal thymectomy for myasthenia gravis Interactive CardioVascular and Thoracic Surgery, February 1, 2006; 5(1): 42 - 46. [Abstract] [Full Text] [PDF]
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