Increase in Incidence of Elderly-onset Patients with Myasthenia Gravis in Nagano Prefecture, Japan

Abstract

Objectives In European countries and the United States the incidence of elderly-onset myasthenia gravis (MG) has recently been increasing. To investigate whether the incidence of the elderly-onset MG has increased in Nagano Prefecture of Japan, we divided the patients into young and elderly groups, and retrospectively examined their incidence.Patients and Methods On the basis of two-step questionnaires sent to hospitals and the patient list of the intractable disease registration system in Nagano Prefecture we studied 213 MG patients diagnosed between 1982 and 2001. This 20-year period was divided into 4 fiveyear terms, and the incidence of MG in young-(younger than 65) and elderly-onset (65 or older) groups was investigated separately for each term.Results The ratio of the elderly-onset group showed a significantly positive correlation with terms irrespective of associated thymoma (r=0.98, p<0.05). There was a significant difference in the mean onset age among the 4 terms (p<0.005). The standardized incidence of MG gradually increased in both young-and elderly-onset groups as well as in the whole age range. The elderly group showed a particularly high incidence in females (12.01/million/year) and in patients without thymoma (8.78/million/year) in the final five years.Conclusions We confirmed that the incidence of elderly-onset MG has recently been increasing in the Nagano Prefecture. Since the change of the age distribution in this district is almost identical to that of the whole country, the incidence of MG might have been increasing in Japan as a whole, particularly in the elderly population.

The Incidence of Myasthenia Gravis: A Systematic Literature Review

“…1 Incidence rate confirmed using data given in paper; 2 age-adjusted to the Libyan population; 3 age-and sex-adjusted to the UK population; 4 age-and sex-adjusted to the world standard population; 5 age-adjusted to 1991 Croatian population; 6 standardised to Doll's world population; 7 no details given about criteria used for diagnosis at onset; Somnier et al [30] note that onset can be up to 2 years before diagnosis; incidence at diagnosis unless otherwise specified; 8 95% confidence limits calculated from data given in paper. vis was not reported on with reference to disease subtype but in the papers that reported the numbers of cases by subtype, the most frequently diagnosed were the mildgeneralised, moderate-severe generalised and ocular subtypes [30][31][32][33]36] .…”

“…Variation over Time Between 1970 and 1990 the incidence rates reported were mainly between 3.0 and 6.0/1,000,000/year [13,16,17,25,26,[31][32][33][34][35] . From 1990 onwards they were higher (6.0-30.0/1,000,000/year) [13-15, 18, 19, 21-24, 27, 28, 33, 36-38] .…”

“…Overestimation of incidence rates was thought to be unlikely where specialists diagnosed or reviewed the cases included [14, 16, 18, 19, 24-27, 29, 32, 36, 37] ; other studies reported reliable case identification [40] , using a 3-year follow-up period to ensure correct diagnosis [23] and a regular clinical follow-up to exclude questionable cases [13] . Another important factor in reducing the possibility of overestimating cases is owing to the changes that have taken place in diagnosing myasthenia gravis [22,28,33,36] : Oosterhuis [31] reported that he retested patients with a diagnosis established before 1985 who were still alive and traceable and found that 26 of 29 patients were positive for anti-AChR antibodies; the remaining patients were thought to have had seronegative myasthenia gravis.…”

Comparison of the histological and immunohistochemical features of the thymus in young- and elderly-onset myasthenia gravis without thymoma

“…In this disease the thymus plays an important role in the induction of the anti-AChR antibodies, and at the present time total thymectomy is accepted as a standard therapy irrespective of associated thymoma, particularly for the generalized type (1,2). Although typical MG is likely to develop in the second to fourth decades (1), the number of elderly patients with this disease has recently increased in Japan as well as in Europe and the United States (3)(4)(5)(6). Because elderly-onset MG patients without thymoma are considered to commonly show extensive fat infiltration in the thymus, it remains unclear whether total thymectomy is the best therapeutic option for these patients or not.…”

Ocular Myasthenia Analysis of Diagnostic and Treatment Options

“…The classic statement of the disease being of old men and young woman is true with an age distribution being bimodal with incidence peaks in the 20's for women and 40's for men (Phillips and Torner 1996;Grob 1999;Mantegazza et al 2003;Matsuda et al 2005). OM is more likely to present at a later age and is more often seen in men .…”