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Late‐onset myasthenia not on the increase: a nationwide register study in D enmark, 1996–2009
Author(s) -
Pedersen E. G.,
Hallas J.,
Hansen K.,
Jensen P. E. H.,
Gaist D.
Publication year - 2013
Publication title -
european journal of neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 124
eISSN - 1468-1331
pISSN - 1351-5101
DOI - 10.1111/j.1468-1331.2012.03850.x
Subject(s) - medicine , incidence (geometry) , myasthenia gravis , pyridostigmine , population , confidence interval , pediatrics , demography , sociology , physics , environmental health , optics
Background An increase in late‐onset myasthenia gravis ( MG ) has been reported. There are few large population‐based studies over longer periods of time reflecting recent developments in MG incidence. Methods We identified a nationwide cohort of patients with incident myasthenia in D enmark in 1996–2009. We used a validated algorithm to track subjects based on a combination of diagnosis and prescription (pyridostigmine) data from nationwide registers. Patients with myasthenia were classified into early onset (<50 years old) and late onset (50+ years). We calculated incidence rates ( IR s) and corresponding 95% confidence intervals. Results We identified 693 patients (362 women) with incident MG in the study period corresponding to an IR of 9.2 per million person‐years (8.5–9.9). Overall, 207 (29.9%) were classified as early‐onset and 486 (70.1%) as late‐onset MG . Women predominated in the early‐onset group (70.5%), but not in the late‐onset group (44.4%). The incidence rate of early‐onset MG was 4.2 (3.6–4.8) and late‐onset MG 18.9 (17.3–20.7) per million person‐years and it did not vary over time in the study period ( P ‐values for trend 0.54 and 0.15, respectively). Conclusion Late‐onset MG comprised a large proportion of all incident cases in D enmark, was more common in men than women, and occurred with a stable incidence in the 14‐year study period. Therefore, we speculate whether previous reports of a rise in late‐onset MG reflect a non‐biological phenomenon, that is, a gradual improvement in the diagnosis of MG in this age group in previous years.