title: Nonthymoma early-onset- and late-onset-generalized myasthenia gravis--a retrospective hospital-based study.
abstract: OBJECTIVE
  Acquired myasthenia gravis (MG) is predominantly due to nicotinic acetylcholine receptor (AChR) autoantibodies (Ab). Differences between nonthymoma early-onset and late-onset MG were reported. We studied the clinical and serological characteristics of nonthymoma AChR Ab-positive-generalized MG patients.
  
  
  METHODS
  Chinese AChR Ab-positive-generalized MG patients who had generalized disease for 3 years or longer were studied.
  
  
  RESULTS
  Among 41 such patients, 25 (61%) were female. The mean onset age was 43.5 years (range 9-78 years) and the mean follow-up duration was 7.8 years (range 3-20 years). Sixteen (39%) patients had late-onset disease (onset age >or=50 years). Compared to early-onset patients (onset age <50 years), late-onset patients were characterized by male predominance (p=0.002), absence of thymic lymphofollicular hyperplasia (p=0.036), and a higher striated muscle Ab seropositivity rate (94% versus 4%, p<0.001). Although there was no statistically significant difference in clinical severity and outcome or response to treatment between late-onset and early-onset patients, 50% and 75% of late-onset patients had moderate or severe disease at onset and worst status, respectively, compared to 28% and 52% for early-onset patients at onset and worst status, respectively. Also 63% of late-onset patients had disease progressed within first 3 years compared to only 40% of early-onset patients did.
  
  
  CONCLUSIONS
  Nonthymoma late-onset-generalized MG patients were common among Hong Kong Chinese, with a statistically non-significant trend that it was clinically more severe than early-onset MG but with similar clinical outcome or response to treatment; >90% of these patients were seropositive for striated muscle Ab.
authors.affiliation: Department of Medicine, Queen Mary Hospital, The University of Hong Kong, Hong Kong, China. koonhochan@hotmail.com
authors.forename: K H
authors.initials: KH
authors.lastname: Chan
authors.forename: R T F
authors.initials: RT
authors.lastname: Cheung
authors.forename: W
authors.initials: W
authors.lastname: Mak
authors.forename: S L
authors.initials: SL
authors.lastname: Ho
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D044466:Asian People / Q000706:statistics & numerical data*; D001323:Autoantibodies / Q000097:blood; D002648:Child; D002675:Child, Preschool; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D008297:Male; D009045:Motor Endplate / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D009157:Myasthenia Gravis / Q000175:diagnosis / Q000453:epidemiology* / Q000628:therapy; D011978:Receptors, Nicotinic / Q000276:immunology; D012189:Retrospective Studies; D012720:Severity of Illness Index
chemical_list: D001323:Autoantibodies; D011978:Receptors, Nicotinic