Myasthenia, Congenital, Refractory To Acetylcholinesterase Inhibitors
Triggs et al. (1992) reported the cases of 3 brothers and a sister, aged 22-43 years, with congenital ptosis, external ophthalmoplegia, proximal muscle weakness, and fatigability unresponsive to acetylcholinesterase inhibitors. Repetitive nerve stimulation showed a significant compound muscle action potential area decrement at 2 or 3 Hz. Nerve conduction studies and concentric needle electromyography were normal. Assessment of individual endplates using single fiber electromyography (SFEMG) with intramuscular axonal microstimulation showed a pattern consistent with a postsynaptic defect of neuromuscular transmission. Edrophonium, an acetylcholinesterase inhibitor, eliminated the decremental response to repetitive nerve stimulation but caused no significant clinical improvement.