CHANGE IN THE PATTERN OF CERVICAL DYSTONIA MIGHT BE THE CAUSE OF BENEFIT LOSS DURING BOTULINUM TOXIN TREATMENT

The muscular patterns of cervical dystonia were identified by polymyog raphic recordings in 76 patients before botulinum toxin treatment. The leading muscles were considered to be those which started dystonic mo vement and which showed constant and maximal activity during all dysto nic movements. The dystonic muscles were repeatedly treated by local i njections of botulinum toxin. Sixteen patients showed (after repeated injections) loss of the benefit of local applications of botulinum tox in after various periods of time. Repeated polymyographic recordings w ere performed in these patients during the loss of the benefit of inje cted botulinum toxin. In four patients repeated polymyographic recordi ngs showed an identical pattern of cervical dystonia, but the activity of previously injected muscles was apparently decreased. In 12 patien ts only minimum or no activity was recorded in muscles which had previ ously been treated with botulinum toxin, but the pattern of cervical d ystonia was changed. Different patterns of cervical dystonia with diff erent leading muscles, but with identical directions of head deviation , were observed in six patients. In another six patients, the head dev iation direction was to the opposite side and was accompanied by a cha nge of the leading muscle and a change of the muscular pattern of dyst onia. These results suggest either that dystonic activity from the cer ebral generator changes to new effecters during the peripheral blockad e of primary dystonic muscles, or that a change of generators at diffe rent levels of the CNS occurs. It may be neccessary to carry out repea ted polymyographic recordings throughout the period of loss of benefit of previously successful local botulinum toxin injections.