[The decrement-increment phenomenon in disorders of neuromuscular transmission by inhibition of acetylcholinesterase]

Abstract

Repetitive stimulation of the median nerve elicited a so far unknown course of the muscle action potentials in four patients with organophosphate intoxications. The amplitude of the initial muscle action potential decreased with the second stimulus and gradually increased to normal values by subsequent stimuli. With the second stimulus a loss of the repetitive muscle action potentials occurred. The Decrement-increment phenomenon was seen in early and/or late stages of severe intoxications when fasciculations were prominent. We suppose that the repetitive muscle action potential following the first stimulus results from backfiring. The second orthodromic nerve action potential collides with this antidromic activity leading to a partial extinction. Loss of backfiring with the second stimulus abolishes the phenomenon of collision and enables a recovery of the muscle action potential amplitudes.