Oromandibular Dystonia (OMD)
Oromandibular dystonia (OMD) is a rare focal neurological disorder that affects mouth, face, and jaws, defined as an involuntary, repetitive, and sometimes sustained muscle contraction of the jaw and perioral muscles.
Dystonia can be anatomically categorized as focal (affecting one or two parts of the body), segmental, multifocal, and generalized. It can also be categorized based on etiology as primary (idiopathic or inherited), or secondary (related to traumatic or surgical incidents, brain diseases, and medications). 
Oromandibular dystonia is a form of a focal dystonia which affects the orofacial region and involves the jaw openers (lateral pterygoids and anterior digastrics), tongue muscles, facial muscles (orbicular oris and buccinator), and platysma. Oral dystonia can affect chewing, speech, swallowing, and facial expression producing functional disability. 
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Oromandibular Dystonia Symptoms
Patients with OMD can have symptoms of involuntary movement or spasm of the lips and tongue, involuntary jaw opening or closing, and lip pursing. They also may complain of muscle pain, which can be due to the hyperactivity and fatigue of masticatory muscles.
Involuntary movements can affect the orofacial region and cause dysphagia, dysphonia, subluxation of the temporomandibular joint, deviation of the mandible, and soft-tissue trauma intraorally. In some patients, there may be a change in the occlusal relationship and slurred speech.
Patients may also complain of excessive drooling as well as problems with mastication, swallowing, and speaking. Additionaly, they might report altered breathing and a feeling of having a foreign object stuck in the throat, as well as problems with opening and closing the jaw that can result in arthralgic or myogenous pain. Initially symptoms are mild; they may become more noticeable over time.
In some cases, OMD is associated with blepharospasm, an involuntary closing of the eyelids; this is referred to as Meige syndrome.
As a result of its infrequent occurrence, OMD is often misdiagnosed and can lead to unnecessary treatment.  It is present at rest, worsens with stress, fatigue or function and usually disappears during sleep.
If the affected muscles are in the oral region it can produce involuntary jaw opening, lateral movements of the jaw and/or protrusion of the tongue. All dystonias are involuntary but tend to be more intermittent than dyskinesias and are comprised of short but sustained muscle contractions that produce twisting and repetitive movements or abnormal postures.  
When oromandibular dystonia occurs in association with blepharospasm (focal dystonia of the orbicularis oculi muscles), it is called Meige’s syndrome, a rare form of segmental dystonia.
When there is no obvious other cause (e.g. dry eyes), blepharospasm is called benign essential blepharospasm, which symptoms range from mildly increased blink rate to forceful eyelid closure sometimes leading to functional blindness. It often affects both eyes at once, but it can also affect only one eye.
Various pathophysiologic mechanisms which have been proposed to explain dystonia, such as trauma, neurodegeneration, basal ganglia and globus pallidus dysfunction, hyperexcitability of interneurons involved in motor signaling, reduced inhibition of spinal cord and brainstem signals coming from supraspinal input, and dysfunction of neurochemical systems involving dopamine, serotonin, noradrenaline, and GABA resulting in abnormal execution of motor control.   
Some dystonias, such as the benign blepharospasm has been associated with enhanced plasticity and disordered sensorimotor integration, producing hyperexcitability on specific muscles. Decreased dopamine has also been implicated as a potential factor in many different forms of dystonia.
During recent years, several gene mutations have also been identified to explain dystonia-plus syndromes and paroxysmal dyskinesia syndromes, as well as aberrant plasticity, dysfunction of transmitters, and irregularities in intracellular signaling. These findings raise questions regarding the role of genetics in dystonia overall and the role of different molecular mechanisms in dystonia pathogenesis.
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