A rare case of unifocal oromandibular dystonia of the temporalis muscle is presented. It was treated with surgical myotomy when initial botulinum toxin A therapy failed after 3 years of repeated injections.
Oromandibular dystonia is a rare and debilitating neurological condition that results in repetitive involuntary sustained (tonic) or spasmodic (clonic) contractions of the masticatory, lingual, perioral and pharyngeal muscles . Clinically it may be present as involuntary jaw opening, jaw closing, jaw deviation and tongue protrusion . The dystonia may be focal (involving one muscle), segmental (involving neighbouring muscles), multifocal or generalised (widespread muscular involvement). The literature reports that dystonias respond well to injections of botulinum toxin A (Botox) but follow-ups are usually short (<12 months) and what happens to patients who develop a tolerance to Botox is rarely reported .
A 36-year-old Caucasian male presented in September 2002 with a 3 month history of involuntary contractions in the left temporalis muscle that were becoming more frequent. Trauma to his tongue and cheek were not infrequent and he was becoming concerned that his left posterior teeth would crack under the sustained contraction of the left temporalis muscle. At his initial presentation he was experiencing about a dozen contractions per day. Clinically, he had a hypertrophied left temporalis muscle that was confirmed on MRI with no evidence of other focal neurological lesions in the basal ganglia. To confirm the diagnosis , he was referred to a specialist neurologist for further investigations to exclude other neurological disorders such as multiple sclerosis and Wilson disease. Based on the diagnosis of focal oromandibular dystonia that was confined to the left temporalis muscle, management was commenced with botulinum toxin A (Botox) injections (50 mouse units) directly into the left temporalis muscle. The initial response was excellent so the injections were repeated every 4 months .
In June 2005, the patient returned to the author because the Botox injections had become ineffective in the preceding 12 months, and the last injection in April 2005 had had no effect. The contractions in the left temporalis muscle had become more intense and he was experiencing over 100 contractions a day. An update MRI showed a significantly hypertrophied left temporalis muscle ( Fig. 1 ) that was similar in size to the original scans in 2002. He was taken to the operating room where, under general anaesthesia, the left temporalis muscle was exposed via a coronal flap ( Fig. 2 ). The beating muscle was detached off the parietal and temporal bones so that the deep temporal nerves could be exposed on the medial aspect ( Fig. 3 ). Both nerves were identified and cauterised, but the muscle continued contracting. The deep aspect of the left temporalis muscle was then surgically excised down to the zygomatic arch leaving only the temporalis tendon attached to the coronoid process of mandible and 5 mm thickness of fan muscle still attached to the temporalis fascia, which was replaced over the skull to prevent hollowing of the temple. Suction drains and a pressure bandage were left in situ for 2 days postoperatively. Recovery was uneventful, but the contractions, although significantly reduced from >100 per day, did not disappear. Histopathology of the resected muscle did not reveal any abnormalities apart from hypertrophy of muscle fibres. Six weeks after surgery the patient reported 3–4 episodes per week. The patient was advised that further surgery in the form of left mandibular coronoidectomy and temporalis tendon release was required, but he did not return for surgery until June 2006. Immediately following the left coronoidectomy and temporalis tendon release, the contractions completely disappeared.