title: A congenital myasthenic syndrome refractory to acetylcholinesterase inhibitors.
abstract: We studied 4 siblings (3 men and 1 woman), ages 22 to 43 years, with congenital ptosis, external ophthalmoplegia, proximal muscle weakness and fatigability unresponsive to acetylcholinesterase (AChE) inhibitors. Repetitive nerve stimulation showed a significant compound muscle action potential (CMAP) area decrement at 2 or 3 Hz. Nerve conduction studies and concentric needle electromyography were normal, and repetitive CMAPs to single nerve stimulation were not observed. Voluntary single fiber electromyography (SFEMG) showed increased jitter and blocking. Assessment of individual end-plates using SFEMG with intramuscular axonal microstimulation showed no uniform relationship between jitter and the rate of stimulation, consistent with a postsynaptic defect of neuromuscular transmission. Edrophonium eliminated the decremental response to repetitive nerve stimulation, but caused no significant clinical improvement, suggesting an additional mechanism for weakness in these patients.
authors.affiliation: Department of Neurology, University of Texas Medical School, Houston.
authors.forename: W J
authors.initials: WJ
authors.lastname: Triggs
authors.forename: A
authors.initials: A
authors.lastname: Beric
authors.forename: I J
authors.initials: IJ
authors.lastname: Butler
authors.forename: S M
authors.initials: SM
authors.lastname: Roongta
mesh_terms: D000328:Adult; D002800:Cholinesterase Inhibitors / Q000627:therapeutic use*; D004491:Edrophonium; D004576:Electromyography; D005260:Female; D005808:Genes, Recessive; D006801:Humans; D008297:Male; D009157:Myasthenia Gravis / Q000151:congenital* / Q000188:drug therapy / Q000235:genetics; D009469:Neuromuscular Junction / Q000502:physiology*; D011950:Receptors, Cholinergic / Q000032:analysis; D006178:Romani People; D009435:Synaptic Transmission / Q000502:physiology*; D013577:Syndrome
chemical_list: D002800:Cholinesterase Inhibitors; D011950:Receptors, Cholinergic; D004491:Edrophonium