Tick paralysis: electrophysiologic studies.

A patient with tick paralysis had motor and sensory nerve conduction studies before and after removal of an engorged tick. The amplitudes of muscle action potentials evoked by stimulation of motor nerves were reduced initially, returning to normal after the tick was removed. Distal motor and sensory latencies also shortened after removal, and conduction velocities were improved 6 months later. Direct stimulation of muscle produced a normal response, and tests of neuromuscular transmission were normal, including the response to edrophonium. These findings are compatible with experimental results showing effects of the toxin on motor nerve terminals as well as on large sensory and motor nerves.