Movement disorders are brought about by changes in specific regions of the nervous system controlling movement—most notably the basal ganglia and cerebellum—causing a breakdown in the normal patterns of signal transmission from the brain to the muscles. This can result in a loss of motor control and impaired coordination as in ataxia, or may produce involuntary movements, or increased muscle tone as in spasticity and dystonia. While some of these disorders are reversible and can be treated, others persist or continue to deteriorate with time and are disabling. Some of the more common types of movement disorders are described below.
Ataxia consists of a lack of motor coordination affecting the use of the hands and upper limbs as in writing or eating, or may affect speech, walking or other voluntary activities. Ataxia is a non-specific clinical manifestation indicating dysfunction in parts of the brain that coordinate movement, such as the cerebellum, or in sensory feedback to the brain. There are multiple causes of ataxia, some hereditary and others acquired. The most well-known hereditary form is Friedreich’s ataxia which is caused by mutations in the Frataxin gene, but many other types of spinocerebellar ataxia due to mutations in over 40 different genes are now recognised, each with its own distinctive clinical features. Some types of ataxia can be treated, but the effectiveness of treatment will depend on identifying the underlying cause with blood tests and brain scans.
Dystonia is a highly variable movement disorder that causes muscles in various parts of the body to contract or spasm involuntarily. These involuntary muscle contractions may result in repetitive spasms, tremors, twisting movements, abnormal postures and deformities, as well as other involuntary movements.
Dystonia is not a single disease but a syndrome – a set of symptoms that cannot be attributed to a single cause but share common elements. Some forms of dystonia may affect a specific body area, such as the neck, face, jaw, eyes, vocal cords, limbs or trunk. Dystonia affects men, women and children of all ages and backgrounds. It can develop in childhood and is often particularly disabling. Dystonia can be genetic in origin, or may be caused by factors such as physical trauma, exposure to certain medications, or other neurological conditions. Over 20 dystonia genes have now been identified in hereditary forms of the condition, but dystonia can also be a symptom of many other genetic disorders.
The causes of dystonia are not yet fully understood, but it is thought to result from a chemical imbalance in deep areas of the brain called the basal ganglia, which are important for controlling movement. Some dystonia patients may suffer from an illness or injury that damages the basal ganglia, but in the majority of cases the underlying cause is unknown. Depending upon the type of dystonia, blood tests or brain scans are necessary to determine the cause.
Some types of dystonia can be treated with medications such as levodopa or benzhexol, but most cases respond poorly or not at all to treatment. Focal types of dystonia, such as blepharospasm, spasmodic torticollis, dystonic tremor and writer’s cramp can be treated effectively with injections of botulinum toxin. The more severe cases may require insertion of a deep brain stimulator.
Tremor is the most common movement disorder in adults and can be of various types. A tremor of the hands and arms while they are at rest (“resting tremor”) is characteristic of Parkinson’s disease, whereas tremors which develop only when the arms are held outstretched (“postural tremor”) or with movement (“kinetic or action tremor”) are more typical of Essential Tremor (ET) or cerebellar disorders, and are often more disabling.
Essential tremor is the most common type of tremor and can occur at any age from childhood through to later life, with an average age of onset of around 45 years. While it can occur sporadically, in some cases it is familial and has a dominant pattern of transmission. No causative genes have yet been identified, but over 11 genes have been found to be associated with ET and are thought to contribute to its origin. Essential tremor is aggravated by stress and anxiety and is typically subdued by consumption of alcohol. As a result, it is not uncommon for people with ET to become dependent on alcohol to control the tremor. The tremor can also improve with administration of beta-blockers, primidone and other medications. In severe cases, insertion of a thalamic deep brain stimulator is necessary and can be very effective in suppressing the tremor and improving quality of life.
Other types of tremor include dystonic tremor, which can affect the head or limbs; orthostatic tremor which affects the legs when standing (“shaky legs syndrome”); neurogenic tremor which occurs in people with chronic neuropathies; and drug-induced tremors, which are usually reversible if the offending medication is stopped.
Restless Leg Syndrome
Restless leg syndrome (RLS) is a common movement disorder that affects as many as 10% of people at some stage in their lives. It occurs particularly at night and interferes with sleep, and may also occur during periods of daytime relaxation. Affected individuals can experience a variety of sensations in the legs, including aching, burning, itching, crawling, tingling, throbbing and pulling sensations, together with a strong urge to keep moving the legs. This results in difficulty falling asleep and may lead to nocturnal sleep deprivation and daytime sleepiness.
The condition may also occur in people with chronic conditions, such as iron deficiency anemia, diabetes, kidney disease, peripheral neuropathy and Parkinson’s disease. In some cases, RLS is triggered by starting an anti-nausea or antidepressant or antipsychotic medication, or it may be aggravated by these medications. Genetic factors are thought to play a part in some cases.
Various medications can be used to treat RLS. These include dopamine agonists (such as pramipexole), dopaminergic agents (such as Sinemet/Madopar), gabapentin or sedatives. However, before commencing any of these it is important to: (i) stop any other medications that may be causing or aggravating the RLS; (ii) avoid alcohol, caffeine and nicotine, which can bring on or worsen the condition; (iii) treat any underlying chronic conditions such as iron deficiency, diabetes or Parkinson’s disease.
Gait disorders are common and are a significant cause of reduced quality of life and loss of independence. Falls are one of the most important consequences of gait disorders, but slow and insecure gait and ‘fear of falling’ are also of great clinical significance. Types of gait disorder are very diverse and can be classified according to the system responsible for the abnormal gait, the underlying disease (e.g. Parkinson’s disease), or by the distinctive features of the gait. Most gait disorders can be diagnosed after obtaining a full history and a detailed neurological examination. The approach to treatment should include an active intervention program to improve balance and reduce the risk of falls, including provision of appropriate walking aids, as well as more specific medical, surgical and physical interventions depending on the underlying cause of the gait disorder.