Myasthenia gravis (MG) is an autoimmune, neuromuscular disorder characterized by fluctuating muscle weakness and fatigability, in which the body’s immune system creates antibodies that attack acetylcholine receptors in neuromuscular junctions. The prevalence reported in Norway in 2007 was 10 pr. 100000 people, and the incidence was 4 pr 1 million inhabitants.
MG is a chronic disorder, but long periods of remission occur. One of the treatment options for MG patients today is thymectomy. This is currently performed based on empirical observations, as the role of thymus in MG is still unclear. In this study, the effect thymectomy has on remission of MG in early debut MG and in late debut MG will be discussed. MG with thymoma has been excluded, as thymectomy always will be removed due to a risk of malignancy.
6 retrospective studies have been analyzed, where 3 studies showed positive correlation between thymectomy and remission, with best results attained when performed in young patients, and least effect in late debut MG. One study concluded that thymectomy was effective in late debut MG. Nevertheless, all studies up till today are retrospective; this opens up for confounding variables, such as use of different operation technique, inconsistent use of MG classification, different definitions of endpoints. There is a general lack of good, class I studies. An evidence based review performed by Gronseth et al, has tried to identify confounders and compared articles with a similar design. They found that there was a positive correlation between thymectomy and remission of MG, and hence the recommendation is that thymectomy should be considered as an alternative to increase the chance of remission. This view has also been adopted by the American Academy of Neurology.
This study emphasizes the importance of using good methodology in retrospective studies. International, standardized and objective variables should be implemented and taken in use by all researchers in future studies, to exclude uncertainty around the results and conclusions drawn. Today’s international neurological guidelines have been based upon the best retrospective studies available so far, and are recommended by neurologists and used internationally.