Dystonia is defined as a syndrome that presents with sustained or intermittent muscle contractions resulting in abnormal repetitive, twisting, patterned movements and abnormal postures. Dystonic movements or postures are initiated or aggravated by voluntary movement (DiFrancesco et al. 2012; Lubarr and Bressman 2010; Roubertie et al. 2000; Madhusudanan 1999; Albanese et al. 2013).

The etiology and pathophysiology of dystonia are not clearly understood. Research suggests that dystonia is a motor system disease rather than disease within a particular motor structure (Lubarr and Bressman 2010). Historically, dysfunction of the basal ganglia was believed to be the cause of the condition, since the basal ganglia is responsible for integration of motor control. However, dystonia had been presented in patients with normal brain structure, with lesions in other areas of the brain or in association with other neurodegenerative syndromes or diseases. Studies suggest that the abnormal twisting movements may be the result of co-contraction of agonist and antagonist muscles. Electromyography (EMG) studies show that there are excessive and overlapping activities in the agonist and antagonist muscles that are not normally involved in a voluntary movement, resulting in prolonged and complex innervations of opposing muscles causing the involuntary dystonic movements and postures (Berardelli et al. 1998). Tempel and Perlmutter (1993) suggested that there may be a sensory feedback component in activation and suppression of dystonia. Vibrations of the dystonic regions can induce involuntary contractions to reproduce dystonic movements and posture. Sensory tricks, such as stroking or touching the affected body part, will reduce the contraction.

Dystonia may involve any body region or combinations of body regions, and the distribution may change over time and spread to previously unaffected regions (Albanese et al. 2013). The distribution of dystonia may be focal, affecting a single body part which often presents as cramps. Dystonia may also be segmental, involving two or more contiguous regions, or it may be generalized to one side of the body or the entire body (Albanese et al. 2013; DiFrancesco et al. 2012; Berardelli et al. 1998).

There are few methods proposed to classify dystonia; however, two classifications are commonly accepted at the present time, primary and secondary dystonia. Primary dystonia presents as the only clinical sign, whether there is a focal or generalized distribution. There is no evidence of an acquired lesion or trauma, and it is not associated with any neurological or metabolic disease or syndrome. (Albanese et al. 2013; Lubarr and Bressman 2010; Berardelli et al. 1998). A number of DYT gene abnormalities have been identified in relation to primary dystonia (Camargo et al. 2015).

Secondary dystonia occurs in association to another disease or is acquired via a lesion or trauma. There may be numerous other neurological symptoms such as spastic dystonia presenting in children with cerebral palsy. There may or may not be an identified gene associated with the condition (Lubarr and Bressman 2010; Albanese et al. 2013). Other methods to classify dystonia may be related to age of onset or associated condition. Table 14.3 outlines the proposed classification of dystonia.

Secondary dystonia may also be caused by preventable conditions related to dietary, metabolic, or chemical imbalances. For example, kernicterus is a condition caused by bilirubin toxicity in newborn babies. The developing brain is vulnerable to exposure to moderate – high levels of bilirubin over time. This exposure results in damage to specific structures including the basal ganglia and cerebellum, thus causing neurological deficits and movement disorders such as dystonia (Ross and Vasser 2015; Okumura et al. 2009). Kernicterus is preventable with careful monitoring and management of hyperbilirubinemia in the neonate.

The presentation of dystonia interferes with performance of general activities of daily living and may cause great pain and discomfort. Dystonia may be present alone or be the clinical manifestation of many associated neurological, metabolic, or acquired conditions. The treatment of dystonia is guided by a thorough history and careful assessment of both clinical and functional effects that include the topography of dystonia, severity of abnormal movements, functional impairments, and progression of disease (Roubertie et al. 2000). Screening tests, laboratory assessments, and diagnostic imaging are needed to distinguish associated diseases and rule out treatable conditions. A number of medications may induce dystonia such as various dopamine antagonists, antiepileptic agents, antihistamines, tricyclic antidepressants, adrenergic agents, monoamine oxidase inhibitors (MAOIs), and caffeine. Therefore, correcting or treating the underlying cause or condition may eliminate the dystonia (Albanese et al. 2006; Geyer and Bressman 2006).

The use of a standardized scale to rate and measure the degree of dystonia is helpful to determine the most appropriate treatment strategies and also to evaluate the effectiveness of treatment modalities. Several scales are used to measure dystonia. The most commonly used scale for primary dystonia is the Burke-Fahn-Marsden (B-F-M) rating scale, and the Barry-Albright Dystonia (BAD) scale is the most popular for secondary dystonia (Comella et al. 2003; Barry and Van Swearingen 1999). Each scale identifies body parts and an ordinal scale is used to rate the severity of the dystonia of individual patients. The scores measure dystonia of individual body parts and the overall total. The scores provide a standard to design treatment plans and offer comparisons to assess the effectiveness of such treatments.

Rehabilitative services and pharmaceuticals are conservative therapies that are effective in management of spasticity and dystonia in the early and mild stages of disease. Rehabilitation with physiotherapy and occupational therapy are also important in combination with more invasive procedures to manage movement disorders. Pharmacotherapy is helpful for selected patients and easy to administer. However, both therapies lose effectiveness as the conditions progress, and increasing medication doses pose dangerous adverse effects that are hard to control making it necessary for more invasive therapies (Goldstein 2001).

The use of botulinum A toxin (Botox) to treat focal spasticity and focal or segmental dystonia has been gaining favor over the past 10–15 years. Botox is a mildly invasive, non-neurosurgical, and temporary treatment for moderate movement disorder. Botox is injected directly into the targeted muscle and causes temporary paralysis of the muscle. It acts by inhibiting acetylcholine release at the neuromuscular junction and affects the muscle spindles and afferent nerve fibers (Koman et al. 2003; Ward et al. 2006; Wong 2003; Guettard et al. 2009).

The effects of Botox are temporary, with effects initiated within 1–2 weeks after the injection and peaking at about 4–6 weeks. The effects last about 4–6 months but are very individualized to the specific patient. The dosing of Botox is calculated by the patient’s weight. There is a mild risk for development of resistance to the toxin that is dependent on the interval and total dose administered. Administrations of doses higher than recommended may cause dysphagia, decreased gastrointestinal motility, and respiratory muscle compromise (Tabbal 2015).

Baclofen is recognized as a medication that is effective in reducing the tone and symptoms of spasticity. It is structurally similar to gamma-aminobutyric acid (GABA) which is the primary inhibitory neurotransmitter in the CNS that promotes relaxation. Baclofen is a GABA agonist and binds to presynaptic GABA receptors to restrict calcium influx at the presynaptic terminal, thereby inhibiting the release of excitatory neurotransmitters across the synaptic junction at the level of the spinal cord to decrease muscle tone (Albright 2003).

Baclofen can be administered both orally and intrathecally via an implanted pump. The primary goals for treatment with baclofen are to decrease muscle tone and improve the functional status of the patient. With dystonia, baclofen helps with relaxation and improves the pain sensation associated with the abnormal movements and postures (Tabbal 2015).

Major adverse effects of baclofen administered orally or intrathecally include sedation, somnolence, seizure activity, muscle weakness, orthostatic hypotension, dizziness, headaches, and ataxia. However, withdrawal of baclofen is the most serious concern related to treatment. Baclofen withdrawal may result in rebound severe spasticity, rigidity, tachycardia, hypotension, hyperthermia, and/or seizures. Thus, it is important that the medication be given at the appropriate dose, at regular intervals, and continuously without abrupt interruptions.

When baclofen is administered orally, the drug is rapidly absorbed and partially metabolized in the liver and then excreted in the kidneys. The half-life is about 3.5 h. Oral baclofen does not readily cross the blood-brain barrier and requires large doses to reach therapeutic concentrations in the cerebrospinal fluid (CSF) at the desired spinal levels.

Intrathecal baclofen (ITB) was first approved in the United States for use to treat spasticity of spinal origin in 1992 and subsequently to treat spasticity of cerebral origin in 1996 (Albright and Ferson 2006). ITB infuses directly into the CSF at the targeted spinal level at high concentrations, although the dose is only a fraction of the oral dose necessary to achieve the same therapeutic effects (Albright and Ferson 2006; Rizzo et al. 2004). Clearance of ITB is via caudal-cephalic bulk flow similar to the flow of CSF in the spine at about 30 ml/h. The drug concentration in the cerebral or brainstem levels is only about one quarter of the concentration found in the lumbar spine region following ITB administration. The risks of dose-related adverse effects and overdose are greatly minimized (Bergenheim et al. 2003; Fitzgerald et al. 2004; Vitztum and Olney 2000). Table 14.4 shows the characteristics of oral baclofen contrasted to intrathecal baclofen.

Withdrawal symptoms are more severe and much more problematic with ITB as compared to oral administration. In addition, abrupt disruption of baclofen administration may result in rhabdomyolysis with elevated plasma creatinine kinase level, renal and hepatic failure, disseminated intravascular coagulation, and sometimes death, if therapy is not restarted promptly. This condition is also known as neuroleptic malignant syndrome and can be life-threatening (Douglas et al. 2005; Mohammed and Hussain 2004).

The literature highly supports ITB for the management of spasticity in both cerebral and spinal origin. Recent longitudinal studies support both efficacy and safety in the continuous use of ITB for children with spasticity or other movement disorders caused by various underlying conditions including cerebral palsy, stroke, multiple sclerosis, myelomeningocele, and head or spinal injury (Bergenheim et al. 2003; Krach et al. 2009; Morton et al. 2011; Ramstad et al. 2010; Ward et al. 2009).