The effect of muscle-tone-reducing procedures in athetotic head movements:partial nerve block by lidocaine and surgical release of the neck muscles

Objective: To investigate the effect of muscle-tone-reducing procedures (MT RPs), i.e. partial nerve block by lidocaine (PNB) and surgical release of m uscle attachment to bone (SRMAB), on incessant involuntary head movements i n athetotic patients. Methods: Pre/post-MTRP changes in neck-muscle activities, glabella movement and maximum isometric forces of the head were measured in six athetotic pa tients with severe spondylotic myelopathy resulting from incessant involunt ary head movements. Results: Pre/post-MTRP changes in neck-muscle activities resembled those af ter gamma-block. In four patients, PNB reduced the maximum isometric force by no more than 40% of pre-PNB force, while decreasing the amount of involu ntary head movements to 37-65% of the pre-PNB value in the frontal plane. M RSAB reduced the force by less than 40% of pre-SRMAB force in 4 MRSAB teste d patients, while decreasing the amount of involuntary head movements to 12 -45% of the pre-SRMAB value in all 6 patients. Conclusion: MTRPs reduced involuntary head movements significantly while pr eserving voluntary muscle forces relatively well. PNB and SRMAB procedures have in common the effect of reducing gain in the myotatic reflex pathway b y decreasing the excitatory inflows to alpha-motoneurons via muscle spindle Ia-afferents, which resulted from blocking mainly gamma-efferent conductio n by PNB, and reducing background tension in muscle spindles by SRMAB. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.