Characteristics of Sensory Trick Maneuvers in Idiopathic Oromandibular Jaw Opening Dystonia

Objective: We have attempted to evaluate the efficacy of different sensory trick manoeuvres in oromandibular dystonia (OMD). Background: Jaw opening OMD is a form of focal dystonia involving lower facial, labial, lingual as well as pterygoid and submental muscles resulting in unvoluntary muscle spasms especially during speaking. As in other forms of dystonia, symptoms may be alleviated by several sensory trick manoeuvres (e.g., biting on a toothpick) although hitherto only little is known about the underlying pathophysiological mechanisms. Methods: In this study we systematically examined a homogeneous group of seven patients with idiopathic jaw opening dystonia performing a standardized counting task with and without the use of a small wooden stick serving as a sensory trick. The following conditions were tested while counting: 1) no use of the stick, 2) stick placed in the mouth between teeth and cheek, 3) slight biting on the stick, and 4) voluntary jaw closure without use of the stick. For further analysis we assessed the following parameters: self-rating using a visual analogue scale, quality of speech using audio recordings for blinded evaluation and surface electromyographic (EMG) recordings from the temporal, perioral, and submental regions. Results: Self-assessment showed a significant reduction of symptoms for both conditions using the stick, while biting on it was most effective (–48%, p<0.015). Analysis of EMG data showed a significant reduction of perioral EMG activity during condition 2 (–28%, p<0.05) whereas biting on the stick (condition 3) had a significant effect mainly on submental muscles (–21%, p<0.01). Although voluntary jaw closure (condition 4) did neither improve speech nor self-assessment, it significantly reduced EMG activity of submental muscles to a similar degree as biting on the stick (–23%, p<0.015). Speech showed no significant changes although there was a trend for condition 3 (biting on the stick, –15.1%, p=0.114). Conclusions: Sensory tricks in jaw opening OMD are an effective and valuable tool to reduce dystonic muscle activity. Besides primary sensory stimulation of the oral region, slight voluntary jaw closure (with or without the use of a stick) decreases dystonic muscle activity indicating that muscle spindle afferents may play a role in the action of sensory trick manouevers. These findings may have therapeutic implications to be used in specific speech training programs for OMD patients. Supported by Dystonia Foundation, USA.