Oromandibular dystonia is characterized by involuntary contraction of the masticatory and tongue muscles, causing difficulties in mastication or speech. Muscle afferent block (MAB) therapy by intramuscular injection of lidocaine and alcohol is aimed at reducing muscle spindle afferents. We treated 37 patients with oromandibular dystonia by intramuscularly injecting 5 to 10ml of 0.5% lidocaine with 0.5 to 1ml of 99.5% alcohol. The muscles for injection were chosen from among the masseter, the inferior head of the lateral pterygoid muscle, the anterior belly of the digastric muscle, the genioglossal muscle, the medical pterygoid muscle, the sternocleidomastoid muscle, and the trapezius muscle. The effect of therapy was assessed subjectively on a linear self-rating scale ranging from 0 (no improvement) to 100 points (complete cure). All patients showed clinical improvement with reduced EMG activity in the affected muscles. The mean number of injections was 10.1±5.8. The overall subjective improvement rate was 60.8±25.4%. Maximal mouth opening (26.0±7.7mm) in patients with restricted mouth opening increased significantly (p<0.0001, t test) after treatment (37.1±7.6mm). Some patients had tenderness, stiffness, or swelling of the muscles after repeated injection. The discomfort disappeared spontaneously after discontinuing therapy. MAB therapy is an effective means of treating oromandibular dystonia that has no major side effects.
