Persistence of local twitch response with loss of conduction to and from the spinal cord.

A local twitch response (LTR) is a brisk contraction of a taut band of skeletal muscle fibers elicited by snapping palpation of a trigger point (TrP) in that band. The LTR is a clinically valuable objective sign that confirms the presence of a myofascial TrP. A transient burst of electromyographic (EMG) activity can be recorded from taut band fibers when an LTR is elicited by snapping palpation of TrP. A previous study of the human extensor digitorum muscle during ischemia suggested that both central and local pathways can be involved in the propagation of LTRs. In this study, EMG activity of LTRs in the third finger extensor muscle were recorded bilaterally in a patient with a unilateral brachial plexus lesion. This patient had complete loss of nerve conduction involving the posterior cord of the right brachial plexus as confirmed by EMG and nerve conduction studies and by neurological examination at 6 months after injury. EMG activity (measured as discharge duration and maximal amplitude) on the paralyzed side was significantly reduced (p < 0.01) as compared with the unaffected side, but had not disappeared. Three more studies were done at 7, 8, and 17 months after injury when the motor and sensory functions were recovered progressively. The EMG activity of LTRs recovered on the paralyzed side in parallel with the motor and sensory recovery. These findings indicate that the transmission of LTR depends mainly on the central nervous system with a possible minor degree of local transmission.