Myasthenia gravis with features of the myasthenic syndrome. An investigation with electrophysiologic methods including single-fiber electromyography.
A 47-year-old woman had myasthenia gravis with only moderate weakness and a consistently poor response to anticholinesterase medication. She was investigated with routine electrophysiologic studies and single-fiber electromyography. The studies showed a limited effect of anticholinesterase medication. There was a decrement to 2 Hz stimulation of not less than 25 percent regardless of medication and administration of edrophonium. With faster rates of stimulation (10 to 20 Hz), there was a facilitation up to 190 percent. In addition, with postcontractive or post-tetanic potentiation the action potential in the abductor digiti minimi muscle was increased from the initial value of 2.5 mv or less to up to 6 mv. Single-fiber electromyographic investigations showed increased jitter and blocking with little response to drugs, as well as facilitation in a large number of motor end-plates in association with both voluntary activity and repetitive stimulation. The findings indicated a mixture of phenomena seen in myasthenia gravis and the myasthenic syndrome.
D000200:Action Potentials; D004359:Drug Therapy, Combination; D004491:Edrophonium; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006801:Humans; D008875:Middle Aged; D009119:Muscle Contraction; D009132:Muscles / Q000166:cytology / Q000503:physiopathology*; D009157:Myasthenia Gravis / Q000188:drug therapy / Q000503:physiopathology* / Q000628:therapy; D009388:Neostigmine / Q000008:administration & dosage / Q000627:therapeutic use; D011729:Pyridostigmine Bromide / Q000008:administration & dosage / Q000627:therapeutic use; D011999:Recruitment, Neurophysiological; D013934:Thymectomy
D009388:Neostigmine; D004491:Edrophonium; D011729:Pyridostigmine Bromide