Understanding Dystonia: A Summary of the Basics

Cervical dystonia (CD) is the most common form of focal dystonia. Cervical dystonia is an ‘umbrella term’ for dystonia that affects muscles in the head and neck. Dystonia where the neck is pushed to one side is called later-ocollis. Dystonia where the chin is tilted to one side is called torticollis, anterocollis is where the head is pushed forward, and retrocolis where the head is pushed back. Tremor is a common feature in CD. Individuals can have one or more forms of cervical dystonia. (Jost et al., 2020; McCambridge & Bradnam, 2021).

Writer's cramp is a task-specific dystonia where abnormal posturing can occur in the fingers, hand and often forearm while writing (Todt et al., 2021). Benign essential blepharospasm is dystonia of the eyelids which induces twitching, excessive blinking and often involuntary closure of the eyes (Byun et al., 2019; Soikas et al., 2019). Oromandibular dystonia is dystonia affecting the lower half of the face, including the masticatory muscles, muscles in the jaw, the tongue, lips, soft palate and pharnyx (Britton et al., 2020).

Dystonia - Parkinsonism is the term used for genetic disorders where both features of dystonia and parkinsonism, bradykinesia, rigidity and tremor, occur concurrently (Weissbach et al., 2021). The severity of dystonia and parkinsonism can vary in each individual. Examples of this disorder include some forms of dopa-responsive dystonia, rapid onset dystonia-parkinsonism disorder, Wilson’s disease, some variants of juvenile Huntington’s disease and some variants of infantile parkinsonism- dystonia disorder (Herzog et al., 2021; Ng et al., 2021).

Myoclonus - dystonia is another collective term for mostly genetic disorders that include myoclonus and features of dystonia. Often in these disorders, myoclonic jerks occur in the neck and upper limbs and dystonia presents as abnormal posturing of the forearm and hands, as well as the presence of cervical dystonia. The lower limbs are much less affected (Blackburn & Parnes, 2021; van der Veen et al., 2019).

Dopamine responsive dystonia is another umbrella term applied to genetic forms of dystonia, where the symptoms improve with the administration of dopaminergic medications, such as levodopa. In this form of dystonia, the symptoms begin in the lower limbs and later progress to the upper limbs. Abnormalities in gait are common. (Dong et al., 2020; Lee et al., 2018).

Dystonia can be drug induced. For example as seen in tardive drug induced dystonia, which is caused from long term use of neuroleptic medications. Alternatively, acute dystonic reactions may be seen following the use of antipsychotics, antiemetics and antidepressant medications (Krause et al., 2022).

Unfortunately, at the present time, there is neither cure nor disease modifying treatment that can slow down or change the course of dystonia. The focus of the treatment for dystonia is based on the concept of symptomatic management and enhancing quality of life (Bledsoe et al. 2020). Thus, the treatment of dystonia is categorised into four main areas including medications, neurotoxins, neuromodulation and rehabilitation.

Medications for the treatment of dystonia must be individualised. Dopaminergic medications used for Parkinson’s disease such as levodopa, dopamine agonists and monoamine oxidase inhibitors (MAOIs) can be effective in the treatment of dystonia particularly in types such as dopa-responsive dystonia (DRD), myoclonus dystonia or rapid-onset dystonia Parkinsonism (Pirio et al., 2017). Responses may vary depending on the condition and levodopa-induced dyskinesia may occur as a side effect (Bledsoe et al. 2020).

Tetrabenazine is a medication that is effective against tardive dystonia and anticholinergic medications, for example benzhexol and benztropine, are most effective in treating generalised dystonia (Jinnah, 2020). Baclofen, a medication more commonly used to treat spasticity, has been effective in treating idiopathic and tardive dystonia (Pirio et al., 2017). Benzodiazepines such as diazepam and clonazepam, are used as second or third -line agents for management of dystonia (Bledsoe et al. 2020).

Another agent used in the treatment of dystonia is botulinum toxin (BoNT) however, the approval for BoNT use for dystonia varies from country to country. In Australia, BoNT has been approved by the Pharmaceutical Benefits Scheme (PBS) for use in cervical dystonia, blepharospasm and spasmodic dysphonia (Bledsoe et al., 2020; Sy & Fernandez, 2021). Other classifications of dystonia that are treated with off-label BoNT include upper limb dystonic tremor, upper and lower limb dystonia and orofacial dystonia. The advantages of using BoNT is the localised effect it has on the affected area of the body, and avoidance of the many systemic side effects that may occur with oral medications (Bledsoe et al. 2020; Jinnah et al., 2020).

Invasive neuromodulation includes techniques such as ablation and deep brain stimulation (DBS) (Sy & Fernandez, 2021). Ablation refers to surgically induced scarring of the affected area of the brain that causes the dystonia, through methods such as thalamotomy and in more recent times, MRI guided high-intensity focused ultrasound (MRgFUS) (Bledsoe et al., 2020). DBS is the most commonly used invasive neurosurgical treatment for dystonia (Bledsoe et al., 2020; Pirio et al., 2017). The DBS target site most used for dystonia is the globus pallidus internus (GPi) (Bledsoe et al. 2020).

Research continues to try and better understand and treat dystonia. Over recent years, surgical treatment options for dystonia have increased due to the advances in neurosurgery (Bledsoe et al., 2020), and while both Deep Brain Stimulation (DBS) and BoTN have revolutionised dystonia treatment, they are not without their therapeutic limitations and are not suitable treatments for all patients (Galpern et al., 2014; Kilic-Berkmen et al., 2021).

Ongoing research aims to refine and increase the effectiveness of methods used to manage dystonia. By identifying similarities in the many forms of dystonia and comparing this to other movement disorders, research aims to understand more about dystonia and how to find more effective treatments (Downs et al., 2020; Galpern et al., 2014).

Due to the many types of dystonia, prognosis varies enormously. For instance, spreading of dystonia from one region to another, has a negative effect on prognosis. Other factors that affect prognosis include, the individual’s response to medications and treatment, and whether individuals experience periods of partial or complete remission from dystonic symptoms (Mainka et al., 2019). In patients with an acquired dystonia, such as drug induced dystonia or dystonia secondary to brain injury, the prognosis depends on the cause of the dystonia, the underlying pathology and available treatment options (Liow et al., 2016; van Edmond et al., 2015)

Looking forward, while effective treatment may require a combination of current therapeutic approaches, new therapies are being developed. Investigations into the effectiveness of methods such as exercise therapy, yoga, music therapy, mindfulness, transcranial electrical stimulation (TES) and transcranial magnetic stimulation (TMS) continue. Further investigation into these methods through well-designed clinical trials are necessary to evaluate their safety, effectiveness and efficacy (Galpern et al., 2014).

Dystonia continues to present as a complex disease, while its disease classification continues to evolve over time. Although dystonia is often a misunderstood disease, ongoing research and clinical trials hope to better understand disease pathophysiology and identify more efficient and effective treatment options.