In which of the following will EMG show decremental response?

Ans. A. M. Gravis* In M. Gravis, the fundamental defect is a decrease in the number of available AChRs at the postsynaptic muscle membrane. These changes result in decreased efficiency of neuromuscular transmission.* Therefore, although ACh is released normally, it produces small end-plate potentials that may fail to trigger muscle action potentials.* The amount of ACh released per impulse normally declines on repeated activity (termed presynaptic rundown).* In the myasthenic patient, the decreased efficiency of neuromuscular transmission combined with the normal rundown results in the activation of fewer and fewer muscle fibers by successive nerve impulses and hence increasing weakness, or myasthenic fatigue.* This mechanism accounts for the decremental response to repetitive nerve stimulation seen on electrodiagnostic testing.