title: Frequency of seronegativity in adult-acquired generalized myasthenia gravis.
abstract: We determined the prevalence of muscle acetylcholine receptor (AChR) antibodies in patients with adult-acquired generalized myasthenia gravis (MG), the seroconversion rate at 12 months, and the prevalence of muscle-specific tyrosine kinase (MuSK) antibody among persistently seronegative patients. We identified 562 consecutive Mayo Clinic patients with MG based on clinical and electrophysiological criteria. At presentation, 508 patients (90.4%) tested positive for AChR binding or AChR modulating antibodies. After 12 months, 15.2% of initially seronegative patients had become seropositive, yielding a seronegativity rate of 8.2% (95% confidence interval: 6.2-9.6%). Among seronegative patients not receiving immunosuppressants, 38% were MuSK antibody-positive and 43% were seropositive for nonmuscle autoantibodies. Classification as seronegative MG should be reserved for nonimmunosuppressed patients with generalized MG who lack muscle AChR binding, AChR modulating, or MuSK antibodies at presentation and at follow-up of at least 12 months.
authors.affiliation: Department of Laboratory Medicine & Pathology, Mayo Clinic, College of Medicine, 200 First Street S.W., Rochester, Minnesota 55905, USA.
authors.forename: Koon Ho
authors.initials: KH
authors.lastname: Chan
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Lachance
authors.forename: C Michel
authors.initials: CM
authors.lastname: Harper
authors.forename: Vanda A
authors.initials: VA
authors.lastname: Lennon
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001323:Autoantibodies / Q000097:blood*; D018450:Disease Progression; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000378:metabolism; D009157:Myasthenia Gravis / Q000097:blood* / Q000276:immunology*; D011863:Radioimmunoassay / Q000379:methods; D020794:Receptor Protein-Tyrosine Kinases / Q000276:immunology*; D011950:Receptors, Cholinergic / Q000276:immunology*; D012189:Retrospective Studies; D012699:Serology / Q000379:methods*
chemical_list: D001323:Autoantibodies; D011950:Receptors, Cholinergic; C095714:MUSK protein, human; D020794:Receptor Protein-Tyrosine Kinases