This study was conducted to clarify non-motor symptoms, such as cognitive ability, psychiatric state, and QOL state, in patients with jaw closing dystonia. The patients examined in this study presented variable symptoms related to pain and movement difficulties beyond the orofacial region, while their awareness of those difficulties and motor deficits in the jaw, tongue, lip, face, and shoulder regions also widely varied.
Recently, Gnand Nag  reported clinical findings of a case of oromandibular dystonia in a 26-year-old female who complained of painful constrictive movements on the right side of the face and a feeling of constriction in the neck, which led to difficulty with breathing. Their patient experienced spontaneous, intermittent, unilateral paroxysmal, and severely painful involuntary spasmodic contractions on the right half of the face, which were repetitive throughout the day and could be relieved by conscious opening of the mouth, only to reappear again with the next occlusal contact. Considering the features reported in that study, it is conceivable that the dysfunctional awareness of pain and movement deficits may have great variety among individual jaw closing dystonia patients.
The jaw closing dystonia subjects in the present study had significantly decreased cognitive abilities as evaluated by MMSE findings. Romano et al.  reported that patients with cranial-cervical dystonia may have impaired cognitive domains related to working memory, processing speed, visual motor ability, and short term memory, while Yang et al.  also suggested that cognitive disabilities are predominant in cervical dystonia patients. In consideration of those previous reports of cognitive disabilities noted in dystonia patients, it is likely that those with jaw closing dystonia are also affected by cognitive decline, similar to cranial and cervical dystonia patients [8, 25]. Additionally, the present patient cohort showed anxious and depressive psychiatric states. Clinical observations have noted psychiatric comorbidities, and frequent co-existence of depression and anxiety in dystonia patients [26, 27]. Thus, it is conceivable that jaw closing dystonia patients may also be affected by anxiety and depression as part of their psychiatric state.
Examinations of our patients with the SCL–90R also revealed aggravated somatization, which is considered to be psychological or emotional distress manifested in the form of physical symptoms related to a medically unexplained situation [28–30]. Mild sensory symptoms such as discomfort in the neck noticed months prior to the development of cervical dystonia, irritation or dry eyes prior to development of blepharospasm, and throat irritation prior to the development of spasmodic dysphonia have been reported [28, 31]. Associations of somatoform disorders with anxiety and depressive states have been reported in cervical dystonia patients [27, 32, 33], thus it is also assumed that jaw closing dystonia patients may develop a somatization state such as medically unexplained physical symptoms in relation to anxious and depressive states.
The present patients showed reduced QOL, based on their OHIP–49 and SF–36 scores. Zurowsky et al.  as well as others have confirmed that psychiatric illnesses have a major impact on QOL of patients with dystonia [34–36]. In our study, the dystonia patients consistently demonstrated lower QOL as compared to the healthy controls. Furthermore, OHIP–49 scores for the present patient cohort were consistent with those reported by Bakke et al.  for patients with Parkinson’s disease. On the other hand, our patients had more severe SF–36 scores than reported for patients with cervical dystonia [38, 39], cranial dystonia , and writer’s cramp [40, 41]. Interestingly, our jaw closing dystonia patients showed a remarkable resemblance to patients with Meige’s syndrome in SF–36 results . Taken together, we consider that jaw closing dystonia can have severe effects on physical QOL state, similar to Meige’s syndrome.
Although the neuroanatomical basis of dystonia is unclear, the basal ganglia have been implicated in its pathophysiology based on observations of secondary dystonia in patients with basal ganglia lesions . Structural lesions in the thalamus, parietal lobe, brainstem, and cerebellum can also cause secondary dystonia. In contrast, that study by Lipowski  showed that the absence of observable neurodegeneration in primary dystonia suggests an underlying neuronal dysfunction of connectivity, plasticity, and synaptic regulation involving the basal ganglia circuitry. Cortical-limbic-striatal dysfunction may be involved in depression and other neuropsychiatric disorders in dystonia patients, while attention-executive cognitive deficit may also develop in patients with young-onset generalized and adult-onset focal and segmental dystonia7]. When considering neuropsychiatric factors [43, 44], sensory and cognitive function , and cognitive motor interactions  related to the basal ganglia, abnormal functioning basal ganglia may be involved in the pathogenesis of non-motor symptoms in dystonia patients, including jaw closing dystonia.
Bruxism, an abnormal repetitive movement disorder characterized by jaw clenching and tooth grinding, is classified as awake and sleep bruxism . Awake bruxism is usually seen as a jaw clenching habit that appears in response to stress and anxiety states, and considered to be primary bruxism, while it does not have a relationship with other medical conditions. In contrast, neurological disorders such as jaw closing dystonia are termed secondary bruxism. In consideration of the clinical differences between awake bruxism and jaw closing dystonia, several similarities and dissimilarities were shown by the results of the present study. That is, awake bruxism [48, 49] and jaw closing dystonia present similar psychiatric states. In contrast, the jaw closing dystonia patients in our study also presented a dissimilarly marked decline of QOL state to a degree greater than that seen in TMD patients [50, 51]. Furthermore, when considering the strong correlation between exacerbation of TMD symptoms and diurnal bruxism previously reported , the oral and physical QOL outcomes of the present study may distinctly characterize jaw closing dystonia, and provide clues for clinical differentiation from awake bruxism patients. Our findings also indicate that cognitive disability might be associated with jaw closing dystonia [53, 54]. Taken together, it is speculated that non-motor symptoms, such as oral and physical QOL outcomes and cognitive disability, may be clinically applicable to differentiate patients with jaw closing dystonia from those with TMD with diurnal bruxism. In addition, though this study included 2 dystonia patients who were partially edentulous, it seems like partial edentulous status and denture wearing may not have a significant influence on QOL in jaw closing dystonia patients .
In summary, even though localization and awareness of pain, and movement difficulties are variable in patients with jaw closing dystonia, non-motor symptoms such as cognition, psychiatric state, and QOL may be prominently aggravated. Considering the pathogeneses of basal ganglia deficiencies, non-motor cognitive and psychiatric symptoms, as well as dystonic motor deficits may develop in association with jaw closing dystonia.