What is the mechanism of incremental response after high frequency RNS in patients with LEMS.
Decreased Ca 2+ influx into the presynaptic nerve terminal (due to antibody attack) results in insufficient release of ACh.
When the nerve is stimulated at sufficiently high frequencies (either by extrinsic high-frequency RNS or by brief volitional exercise), recurrent depolarization of the nerve terminal causes such a high rate of calcium influx that it overwhelms the nerve cell’s mechanisms for calcium clearance, temporarily increasing intracellular calcium levels and normalizing the release of ACh.
This manifests as a dramatic increase in compound muscle action potential size.
However, low-frequency RNS results in decrement, which may be confused with the decrement of MG.
