• Energy Research

Jaw-deviation dystonia is characterized by the lateral shift of the mandible due to involuntary masticatory muscle contraction, causing difficulties in speech or mastication. We evaluated a patient with jaw-deviation dystonia by recording movement-related cortical potentials (MRCPs) and treated with muscle afferent block (MAB). MRCP associated with mandibular movements (mouth opening, closing, and left and right lateral movements) was recorded in the patient and ten age-matched healthy subjects. In the control subjects, the amplitude of Bereitschaftspotential (BP)/negative slope (NS') was significantly higher for left lateral movements than for the mouth closing. The cortical map of BP/NS' prior to mouth opening and closing showed symmetric distribution, whereas those of lateral movements showed a slight predominance in the ipsilateral hemisphere. The patient showed lower amplitude as compared with control subjects. The right lateral movement (homonymous task) showed task-specific markedly reduced potentials. After MAB by intramuscular injection of lidocaine and ethanol to the inferior head of the left lateral pterygoid muscle, the deviation abolished and severity in speech and mastication was significantly improved. This study suggests that jaw-deviation dystonia might have the same etiology as other focal dystonias.

AbstractOromandibular dystonia is a focal dystonia involving the masticatory and tongue muscles, causing difficulties in speech or mastication. We treated 13 patients with this condition by injecting diluted lidocaine and alcohol intramuscularly. This method is aimed at reducing muscle spindle afferent activity. The symptoms had been resistant to other therapies such as pharmacotherapy or dental treatment. All patients showed clinical improvement after this therapy with reduced EMG activities in the affected muscles, whereas control injection of normal saline gave no changes in EMG activities. The overall subjective improvement was 57.7 ± 25.1% (mean ± standard deviation) in a self‐rating scale. The mean response of the jaw elevator muscles (70 ± 13.1%) was significantly higher (p < 0.02, t test) than that of the depressor muscles (38 ± 28.4%). Despite the precise mechanism being unknown, this difference might be related to the smaller number of muscle spindles in the depressor than the elevator muscles. This therapy is useful for the treatment of drug‐resistant oromandibular dystonia.

Jaw-opening and jaw-deviation dystonias are characterized by mouth opening or lateral shift of the mandible due to involuntary contraction of the lateral pterygoid muscle, causing difficulties in speech or mastication. We introduce the method of muscle afferent block by using a removable device for inserting a hollow electromyographic needle.A technique for fabricating a customized needle insertion guide into the lateral pterygoid muscle is described. Using the device, intramuscular injection of lidocaine and ethanol was performed in 3 patients with jaw-opening dystonia and 2 with jaw-deviation dystonia. Subjective improvement was assessed on a linear self-rating scale ranging from 0 (no improvement) to 100 points (complete cure).The overall subjective improvement was 72% +/- 16.4% without major side effects.The device is very useful for safe and accurate injection into the lateral pterygoid muscle. The muscle afferent block is effective for jaw-opening and jaw-deviation dystonias.