Abstract
Dystonia is a common movement disorder, involving sustained muscle contractions, often resulting in twisting and repetitive movements and abnormal postures. Dystonia may be primary, as the sole feature (isolated) or in combination with other movement disorders (combined dystonia), or as one feature of another neurological process (secondary dystonia). The current hypothesis is that dystonia is a disorder of distributed brain networks, including the basal ganglia, cerebellum, thalamus and the cortex resulting in abnormal neural motor programs. In comparison, functional dystonia (FD) may resemble other forms of dystonia (OD) but has a different pathophysiology, as a subtype of functional movement disorders (FMD). FD is the second most common FMD and amongst the most diagnostically challenging FMD subtypes. Therefore, distinguishing between FD and OD is important, as the management of these disorders is distinct. There are also different pathophysiological underpinnings in FD, with for example evidence of involvement of the right temporoparietal junction in functional movement disorders that is believed to serve as a general comparator of internal predictions/motor intentions with actual motor events resulting in disturbances in self-agency. In this article, we present a comprehensive review across the spectrum of FD, including oromandibular and vocal forms and discuss the history, clinical clues, evidence for adjunctive “laboratory-based” testing, pathophysiological research and prognosis data. We also provide the approach used at the Massachusetts General Hospital Dystonia Center toward the diagnosis, management and treatment of FD. A multidisciplinary approach, including neurology, psychiatry, physical, occupational therapy and speech therapy, and cognitive behavioral psychotherapy approaches are frequently required; pharmacological approaches, including possible targeted use of botulinum toxin injections and inpatient programs are considerations in some patients. Early diagnosis and treatment may help prevent unnecessary investigations and procedures, while facilitating the appropriate management of these highly complex patients, which may help to mitigate frequently poor clinical outcomes.
Highlights
Dystonia is a common movement disorder involving sustained muscle contractions, often resulting in twisting and repetitive movements and abnormal postures related to an imbalance of agonist and antagonist muscles [1]
We present a comprehensive review of the historical context, clinical clues and features differentiating Functional dystonia (FD) from OD across the spectrum of FD subtypes, evidence for adjunctive “laboratory-based” testing, and pathophysiology
While use of targeted antidepressant or anxiolytic treatment, or treatment of neuropathic pain may be beneficial in FD, other typical medications used in the treatment of dystonia and certainly deep brain stimulation (DBS), should be avoided in FD [212, 213]
Summary
Dystonia is a common movement disorder involving sustained muscle contractions, often resulting in twisting and repetitive movements and abnormal postures related to an imbalance of agonist and antagonist muscles [1]. With an estimated prevalence of up to 1 in 1,000 individuals, which is notable, given diagnostic challenges frequently leading to misdiagnosis or under-diagnosis [3, 4]. Functional dystonia (FD) may resemble other forms of dystonia (OD) but has a different pathophysiology [10, 11], as a subtype of functional movement disorders (FMD) under the more general classification of functional neurological disorders (FND) [12]. We present a comprehensive (long-form) review of the historical context, clinical clues and features differentiating FD from OD across the spectrum of FD subtypes (including pediatric FD), evidence for adjunctive “laboratory-based” testing, and pathophysiology. We outline the approach used at the Massachusetts General Hospital (MGH) Dystonia Center toward the diagnosis, management and treatment of this complex set of disorders
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