Carr et al. BMC Neurology 2010, 10:46 http://www.biomedcentral.com/1471-2377/10/46 Open Access RESEARCH ARTICLE © 2010 Carr et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons At- tribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Research article A systematic review of population based epidemiological studies in Myasthenia Gravis Aisling S Carr* 1 , Chris R Cardwell 2 , Peter O McCarron 2 and John McConville 1,3 Abstract Background: The aim was to collate all myasthenia gravis (MG) epidemiological studies including AChR MG and MuSK MG specific studies. To synthesize data on incidence rate (IR), prevalence rate (PR) and mortality rate (MR) of the condition and investigate the influence of environmental and technical factors on any trends or variation observed. Methods: Studies were identified using multiple sources and meta-analysis performed to calculate pooled estimates for IR, PR and MR. Results: 55 studies performed between 1950 and 2007 were included, representing 1.7 billion population-years. For All MG estimated pooled IR (eIR): 5.3 per million person-years (C.I.:4.4, 6.1), range: 1.7 to 21.3; estimated pooled PR: 77.7 per million persons (C.I.:64.0, 94.3), range 15 to 179; MR range 0.1 to 0.9 per millions person-years. AChR MG eIR: 7.3 (C.I.:5.5, 7.8), range: 4.3 to 18.0; MuSK MG IR range: 0.1 to 0.32. However marked variation persisted between populations studied with similar methodology and in similar areas. Conclusions: We report marked variation in observed frequencies of MG. We show evidence of increasing frequency of MG with year of study and improved study quality. This probably reflects improved case ascertainment. But other factors must also influence disease onset resulting in the observed variation in IR across geographically and genetically similar populations. Background Myasthenia gravis (MG) is an archetypal autoimmune disorder in which muscle weakness occurs as a result of impairment of neuromuscular transmission. It is likely to occur as the result of a number of disease entities that result in an indistinguishable clinical picture [1]. There are paraneoplastic forms (thymoma-associated) and non- paraneoplastic forms and the disorder is immunologically heterogeneous - for example serum antibodies can be detected to muscle acetylcholine receptors (AChR-Ab) [2] or the muscle-specific receptor tyrosine kinase (MuSK-Ab) [3], but not both in the same patient. From case series and epidemiological studies, a bimodal distri- bution of MG IR has been frequently described suggest- ing a hormonal or environmental influence on disease onset. MG occurs in both sexes, at all ages and in all races [4]. A large number of MG epidemiological studies have been performed worldwide over the last 60 years with marked variability in observed incidence and prevalence of the disease. Systematic review of MG epidemiology has been carried out in the past by Phillips [5]; but 28 further studies have been performed since and this review pre- dates the discovery of MuSK-Ab MG. In his review, Phil- lips commented upon apparent increasing IR and PR with time but without similar change in MR, and proposed that these trends were due to improved diagnosis and a changing natural history of disease related to better treat- ment. The aim of this review was to summarize the findings of all population-based epidemiological studies of myas- thenia gravis (MG) paying attention to serological sub- type-specific studies and age- and sex- specific incidence. We sought to establish if there is a consensus in IR, PR and MR of MG worldwide and investigate any trends or differences in observed rates over time and in popula- tions. * Correspondence: aisling.carr@belfasttrust.hscni.net 1 Department of Neurology, Royal Victoria Hospital, Belfast, Northern Ireland, UK Full list of author information is available at the end of the article