Movement disorders are a complex group of disorders spanning all aspects of neurological illnesses and range from conditions characterized by too little movement (hypokinesis) to those where movement is excessive (hyperkinesis) . Movement disorders are defined as either an excess of movement or a paucity of voluntary and automatic movement, unrelated to organic weakness or spasticity.
Recently, awareness that movement disorders rank among the most common neurological diseases has been increasing. While most movement disorders are chronic and degenerative, some can develop abruptly and require acute management. Wenning et al. showed that movement disorders are relatively common, with a prevalence rate of 30% in the general population.  
The term “orofacial motor disorder” (OMD) encompasses a spectrum of movement aberrations, both hyperactive and hypoactive, which involves the muscles of the orofacial complex and are innervated by cranial nerves V, VII, and XII. 
An understanding of orofacial movement disorders (OMD) is essential to the clinician interested in treating orofacial pain. It is not uncommon for OMD to be misdiagnosed as temporomandibular disorders (TMD) or to be mislabeled as a psychiatric manifestation resulting in inappropriate treatments. Orofacial motor disorders should thus be a diagnostic consideration in patients presenting with orofacial pain. 
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Orofacial Motor Disorders
We will focus on the hyperactive motor disorders that have their primary presentation in the orofacial region (masticatory system and its adjacent muscles), such as: Orofacial dystonia, bruxism, drug-induced dystonic-type extrapyramidal reactions, secondary masticatory muscle spasms, hemi-masticatory spasms, hemi-facial spasms, oromandibular dyskinesia, synkinesis, hyperactivity of the tongue, masseteric and temporalis hypertrophy, orofacial motor tics, and palatal myoclonus.   
Other Motor Disorders
There are other motor disorders that have an influence on the orofacial muscles, including Parkinson’s disease, dementia related tremor, and post-stroke paralysis; however, we will not discuss those conditions. We will also not cover the hypoactive disorders of the masticatory and facial muscle system (Bell’s palsy or motor nerve transaction with paralysis and focal atrophy).
The term orofacial motor disorder (OMD) covers a wide spectrum of movement aberrations that may be hyperactive, hypertrophic, and restrictive or hypoactive. The hyperactive OMD’s are thought to be driven by alterations in central nervous system functioning.  
Symptoms of Orofacial Motor Disorders
The most common orofacial motor disorder is sleep bruxism and when severe causes pain and dysfunction in the masticatory system. Bruxism is not the only oral motor disorder that can cause headaches, damage the temporomandibular joint and because many of the others in the above list occur during the day (dystonia, dyskinesia, spasm), they can create such motor control difficulty that patients will be unable to eat and may start to lose weight. Sometimes these motor disorders can affect the tongue musculature to such a degree that it compromises the patient’s ability to speak clearly.
Such changes are not only an embarrassment which patients must endure, but it affects their daily living and many patients will refuse, or strongly avoid, public events. Fortunately, there are medications which suppress the motor system and injectable agents such as botulinum neurotoxin (BoNT) and selective surgical interventions that have been shown to reduce the severity of the OMD’s.
Diagnosing Orofacial Motor Disorders
The most important aspect of any clinician’s skill is the ability to provide a differential diagnosis. With the possible exception of bruxism and masseteric hypertrophy, all of the other motor disorders will require a neurologic workup and often a brain MRI and a consultation with a neurologist to achieve a definitive diagnosis. This is necessary in order to rule out the possibility that the motor dysfunction may be due to a tumor, central degenerative, demyelinating, or sclerotic lesion of the nervous system. Fortunately for the patient, tumors and CNS degenerative diseases are uncommon.
Depending on the exact nature of the motor disorder, the examining specialist may add to the work up a thorough family, medication and illegal drug history. The neurologist will typically order standard, enhanced and angiographic-type magnetic resonance imaging of the brain and spinal cord to rule in or out a neurologic infarct, tumor, or compression of critical nerves or brain tissue.
Motor Disorders During Sleep
For those motor disorders that are occurring during sleep (e.g. bruxism) it may be necessary to conduct a polysomnogram which includes an electromyographic assessment of the involved muscles.
For the dystonias that affect a specific motor system (e.g. blepharospasm or torticollis) it is necessary to assess that system thoroughly to ensure that no local infection, neoplastic or arthritic disease is present that might be damaging or irritating the involved peripheral motor nerve branch.
For all of the oral motor disorders it is necessary to conduct a careful examination to rule out local pathologic entities.
Related Reading: Treating Oromandibular Dystonia
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