title: Neuromuscular junction disorders mimicking myopathy.
abstract: BACKGROUND
  Small-amplitude, short-duration motor unit action potentials are non-specific findings seen in myopathies and neuromuscular junction (NMJ) disorders. NMJ studies (repetitive nerve stimulation and single-fiber electromyography) can determine if such findings are related to NMJ abnormalities but are not considered routinely in atypical cases.
  
  
  METHODS
  Medical records of 338 patients with confirmed NMJ disorders were reviewed to identify cases with a clinical or electrodiagnostic impression of myopathy during initial evaluation. A history of muscle biopsy with findings that did not support a myopathic process was required for inclusion.
  
  
  RESULTS
  Four patients met the inclusion criteria. NMJ studies were abnormal in all cases. One patient had elevated acetylcholine receptor antibodies. Three patients were antibody negative: 2 demonstrated immunotherapy responsiveness, and 1 had a Rapsyn mutation.
  
  
  CONCLUSIONS
  NMJ disorders may mimic myopathies, and NMJ studies should be performed to clarify so-called "myopathic" electromyographic findings to avoid unnecessary testing and delayed diagnosis.
authors.affiliation: The Ohio State University College of Medicine, Columbus, Ohio, USA.
authors.forename: Phillip C
authors.initials: PC
authors.lastname: Mongiovi
authors.forename: Bakri
authors.initials: B
authors.lastname: Elsheikh
authors.forename: Victoria H
authors.initials: VH
authors.lastname: Lawson
authors.forename: John T
authors.initials: JT
authors.lastname: Kissel
authors.forename: W David
authors.initials: WD
authors.lastname: Arnold
mesh_terms: D000293:Adolescent; D000906:Antibodies / Q000097:blood; D001706:Biopsy; D003402:Creatine Kinase / Q000097:blood; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006801:Humans; D018482:Muscle, Skeletal / Q000503:physiopathology; D009135:Muscular Diseases / Q000175:diagnosis* / Q000503:physiopathology*; D020511:Neuromuscular Junction Diseases / Q000503:physiopathology*; D011950:Receptors, Cholinergic / Q000276:immunology; D012189:Retrospective Studies
chemical_list: D000906:Antibodies; D011950:Receptors, Cholinergic; D003402:Creatine Kinase
keywords: action potentials; electromyography; myasthenia gravis; neuromuscular junction disorders; repetitive nerve stimulation