Each practice recommendation is rated based on the strength of the evidence. Definitions of the strength of the recommendations (standard, guideline, practice option, practice advisory) and quality of the evidence (Class I-Class III) are presented at the end of the Major Recommendations field.
Conclusions
After systematically reviewing the controlled but nonrandomized studies describing outcomes in myasthenia gravis patients undergoing and not undergoing thymectomy the authors found:
- positive associations in most studies between
thymectomy and myasthenia gravis remission and improvement (median relative
rate of medication-free remission, 2.1; asymptomatic, 1.6; improvement, 1.7)
- confounding differences in baseline characteristics of
prognostic importance between thymectomy and nonthymectomy patient groups in
all studies
- persistent positive associations between thymectomy and
improved myasthenia gravis outcomes after controlling for single confounding
variables such as age, gender, and severity of myasthenia gravis
- conflicting associations between thymectomy and improved myasthenia gravis outcomes in studies controlling for multiple confounding variables simultaneously
The authors cannot determine from the available studies whether the observed association between thymectomy and improved myasthenia gravis outcome was a result of a thymectomy benefit or was merely a result of the multiple differences in baseline characteristics between the surgical and nonsurgical groups. Based on these findings, the authors conclude that the benefit of thymectomy in non-thymomatous autoimmune myasthenia gravis has not been established conclusively.
Practice Recommendation
For patients with nonthymomatous autoimmune myasthenia gravis, thymectomy is recommended as an option to increase the probability of remission or improvement (Class II).
Definitions:
Classification of Evidence
Class I: Evidence provided by one or more well-designed randomized controlled trials, including overviews (meta-analyses) of such trials.
Class II: Evidence provided by well-designed observational studies with concurrent controls (e.g., case–control and cohort studies).
Class III: Evidence provided by expert opinion, case series, and studies with historical controls.
Strength of Recommendations
Standards: A principle for patient management that reflects a high degree of clinical certainty (usually this requires Class I evidence that directly addresses the clinical question or overwhelming Class II evidence when circumstances preclude randomized clinical trials).
Guidelines: A recommendation for patient management that reflects moderate clinical certainty (usually this requires Class II evidence or a strong consensus of Class III evidence).
Practice option: A strategy for patient management for which the clinical utility is uncertain (inconclusive or conflicting evidence or opinion).
Practice advisory: A practice recommendation for emerging and/or newly approved therapies or technologies based on evidence from at least one Class I study. The evidence may demonstrate only a modest statistical effect or limited (partial) clinical response, or notable cost–benefit questions may exist. Substantial (or potential) disagreement among practitioners or between payers and practitioners may exist.
