title: Decrement pattern in Lambert-Eaton myasthenic syndrome is different from myasthenia gravis.
abstract: The decrement pattern at low rates of repetitive nerve stimulation in myasthenia gravis (MG) is characterized by a decrease of compound muscle action potential size within the first 4-5 responses. With subsequent stimuli, compound muscle action potential size either increases or does not change. Following an observation that the pattern of decrement might be different in patients with Lambert-Eaton myasthenic syndrome (LEMS), we retrospectively studied traces from eight LEMS patients and 14 patients with seropositive generalized MG, calculating decrement percent from first to fourth and from first to ninth compound muscle action potential. In the LEMS patients, compound muscle action potential amplitude decreased progressively from first to ninth stimulus at 2, 3 or 5Hz in all traces but one. In contrast, MG patients demonstrated the expected improvement after the initial decrement in all traces except one. In the evaluation of patients suspected of having myasthenia gravis, the finding of progressive decrement pattern at low rates of repetitive nerve stimulation may alert the electromyographer to the possibility of Lambert-Eaton syndrome and prompt the performance of further electrodiagnostic tests.
authors.affiliation: Department of Neurology, Istanbul Faculty of Medicine, Istanbul University, 34390 Capa, Istanbul, Turkey.
authors.forename: M Baris
authors.initials: MB
authors.lastname: Baslo
authors.forename: Feza
authors.initials: F
authors.lastname: Deymeer
authors.forename: Piraye
authors.initials: P
authors.lastname: Serdaroglu
authors.forename: Yesim
authors.initials: Y
authors.lastname: Parman
authors.forename: Coskun
authors.initials: C
authors.lastname: Ozdemir
authors.forename: Marina
authors.initials: M
authors.lastname: Cuttini
mesh_terms: D000328:Adult; D003937:Diagnosis, Differential; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006801:Humans; D015624:Lambert-Eaton Myasthenic Syndrome / Q000175:diagnosis* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000175:diagnosis* / Q000503:physiopathology*; D009431:Neural Conduction; D012189:Retrospective Studies