Oromandibular dystonia (OMD) is a form of focal dystonia that involves the masticatory, lower facial, labial and lingual musculature. The term “cranial dystonia” is used when oromandibular dystonia occurs in association with blepharospasm. This particular combination is often referred to as Meige’s syndrome (reviewed by Bhidayasiri et al., 2006).
Epidemiology, clinical features and etiology
Oromandibular dystonia frequently affects women more than men and the prevalence was estimated to be around 68.9 cases per 1 million in the USA (Bhidayasiri et al., 2006). The mean age at onset is between 50 and 60 years. The involvement of masticatory muscles in OMD may cause jaw closing or jaw opening, lateral deviation, protrusion, retraction, or a combination of these. These movements often result in involuntary biting of the tongue, cheek or lips and difficulty with speaking and chewing. Its appearance is often socially embarrassing and disfiguring. In patients with jaw-closing OMD, dystonic spasms of the temporalis and masseter muscles may result in clenching or trismus and grinding of the teeth or bruxism. Jaw-opening OMD commonly involves the lateral pterygoids, anterior belly of the digastric muscle and other submental muscles; contractions of these muscles may lead to some degree of anterocollis. The effects of OMD may be alleviated by different proprioceptive sensory inputs (“sensory tricks”). These include touching the lips or chin, chewing gum or biting on a toothpick. Coexistence with dystonia in other regions and presences of sensory tricks is more common in jaw-opening than jaw-closing OMD. The contraction of mouth and pharynx muscles may cause involuntary vocalizations, occasionally confounded with vocal tics. In addition to the dystonic symptoms, many patients with OMD complain of tension-type headache, dental wear, temporomandibular joint syndrome and, more rarely, temperomandibular joint dislocation, resulting in upper airway collapse.