Dystonia

 

Dystonia is a neurological movement disorder syndrome in which sustained or repetitive muscle contractions result in twisting and repetitive movements or abnormal fixed postures. The movements may resemble a tremor. Dystonia is often intensified or exacerbated by physical activity, and symptoms may progress into adjacent muscles.

The disorder may be hereditary or caused by other factors such as birth-related or other physical trauma, infection, poisoning (e.g., lead poisoning) or reaction to pharmaceutical drugs, particularly neuroleptics., or stress. Treatment must be highly customized to the needs of the individual and may include oral medications, chemodenervation botulinum neurotoxin injections, physical therapy, or other supportive therapies, and surgical procedures such as deep brain stimulation.

Signs and Symptoms
Symptoms vary according to the kind of dystonia involved. In most cases, dystonia tends to lead to abnormal posturing, in particular on movement. Many sufferers have continuous pain, cramping, and relentless muscle spasms due to involuntary muscle movements. Other motor symptoms are possible including lip smacking.

Early symptoms may include loss of precision muscle coordination (sometimes first manifested in declining penmanship, frequent small injuries to the hands, and dropped items), cramping pain with sustained use, and trembling. Significant muscle pain and cramping may result from very minor exertions like holding a book and turning pages. It may become difficult to find a comfortable position for arms and legs with even the minor exertions associated with holding arms crossed causing significant pain similar to restless leg syndrome. Affected persons may notice trembling in the diaphragm while breathing, or the need to place hands in pockets, under legs while sitting or under pillows while sleeping to keep them still and to reduce pain. Trembling in the jaw may be felt and heard while lying down, and the constant movement to avoid pain may result in the grinding and wearing down of teeth, or symptoms similar to temporomandibular joint disorder. The voice may crack frequently or become harsh, triggering frequent throat clearing. Swallowing can become difficult and accompanied by painful cramping.

Electrical sensors (EMG) inserted into affected muscle groups, while painful, can provide a definitive diagnosis by showing pulsating nerve signals being transmitted to the muscles even when they are at rest. The brain appears to signal portions of fibers within the affected muscle groups at a firing speed of about 10 Hz causing them to pulsate, tremble and contort. When called upon to perform an intentional activity, the muscles fatigue very quickly and some portions of the muscle groups do not respond (causing weakness) while other portions over-respond or become rigid (causing micro-tears under load). The symptoms worsen significantly with use, especially in the case of focal dystonia, and a “mirror effect” is often observed in other body parts: Use of the right hand may cause pain and cramping in that hand as well as in the other hand and legs that were not being used. Stress, anxiety, lack of sleep, sustained use and cold temperatures can worsen symptoms.

Direct symptoms may be accompanied by secondary effects of the continuous muscle and brain activity, including disturbed sleep patterns, exhaustion, mood swings, mental stress, difficulty concentrating, blurred vision, digestive problems, and short temper. People with dystonia may also become depressed and find great difficulty adapting their activities and livelihood to a progressing disability. Side-effects from treatment and medications can also present challenges in normal activities.

In some cases, symptoms may progress and then plateau for years, or stop progressing entirely. The progression may be delayed by treatment or adaptive lifestyle changes, while forced continued use may make symptoms progress more rapidly. In others, the symptoms may progress to total disability, making some of the more risky forms of treatment worth considering. In some cases with patients who already have dystonia, a subsequent tramatic injury or the effects of general anethesia during an unrelated surgery can cause the symptoms to progress rapidly.

An accurate diagnosis may be difficult because of the way the disorder manifests itself. Sufferers may be diagnosed as having similar and perhaps related disorders including Parkinson’s disease, essential tremor, carpal tunnel syndrome, TMD, Tourette’s syndrome, conversion disorder or other neuromuscular movement disorders. It has been found that the prevalence of dystonia is high in individuals with Huntington’s disease, where the most common clinical presentations are internal shoulder rotation, sustained fist clenching, knee flexion, and foot inversion. Risk factors for increased dystonia in patients with Huntington’s disease include long disease duration and use of antidopaminergic medication.

Causes
Primary dystonia is suspected when the dystonia is the only sign and there is no identifiable cause or structural abnormality in the central nervous system. Researchers suspect it is caused by a pathology of the central nervous system, likely originating in those parts of the brain concerned with motor function—such as the basal ganglia and the GABA (gamma-aminobutyric acid) producing Purkinje neurons. The precise cause of primary dystonia is unknown. In many cases it may involve some genetic predisposition towards the disorder combined with environmental conditions.

Secondary dystonia refers to dystonia brought on by some identified cause, such as head injury, drug side effect (e.g. tardive dystonia), or neurological disease (e.g. Wilson’s disease).

Meningitis and encephalitis caused by viral, bacterial, and fungal infections of the brain have been associated with dystonia. The main mechanism is inflammation of the blood vessels, causing restriction of blood flow to the basal ganglia. Other mechanisms include direct nerve injury by the organism or a toxin, or autoimmune mechanisms.

Environmental and task-related factors are suspected to trigger the development of focal dystonias because they appear disproportionately in individuals who perform high precision hand movements such as musicians, engineers, architects, and artists.[citation needed] Chlorpromazine can also cause dystonia, which can be often misjudged as a seizure. Neuroleptic drugs often cause dystonia, including oculogyric crisis.

Misfunction of the sodium-potassium pump may be a factor in some dystonias. The Na+
-K+
pump has been shown to control and set the intrinsic activity mode of cerebellar Purkinje neurons. This suggests that the pump might not simply be a homeostatic, “housekeeping” molecule for ionic gradients; but could be a computational element in the cerebellum and the brain. Indeed, an ouabain block of Na+
-K+
pumps in the cerebellum of a live mouse results in it displaying ataxia and dystonia. Ataxia is observed for lower ouabain concentrations, dystonia is observed at higher ouabain concentrations. A mutation in the Na+
-K+
pump (ATP1A3 gene) can cause rapid onset dystonia parkinsonism. The parkinsonism aspect of this disease may be attributable to malfunctioning Na+
-K+
pumps in the basal ganglia; the dystonia aspect may be attributable to malfunctioning Na+
-K+
pumps in the cerebellum (that act to corrupt its input to the basal ganglia) possibly in Purkinje neurons.

Cerebellum issues causing dystonia is described by Filip et al. 2013: “Although dystonia has traditionally been regarded as a basal ganglia dysfunction, recent provocative evidence has emerged of cerebellar involvement in the pathophysiology of this enigmatic disease. It has been suggested that the cerebellum plays an important role in dystonia etiology, from neuroanatomical research of complex networks showing that the cerebellum is connected to a wide range of other central nervous system structures involved in movement control to animal models indicating that signs of dystonia are due to cerebellum dysfunction and completely disappear after cerebellectomy, and finally to clinical observations in secondary dystonia patients with various types of cerebellar lesions. It is proposed that dystonia is a large-scale dysfunction, involving not only cortico-basal ganglia-thalamo-cortical pathways, but the cortico-ponto-cerebello-thalamo-cortical loop as well. Even in the absence of traditional “cerebellar signs” in most dystonia patients, there are more subtle indications of cerebellar dysfunction. It is clear that as long as the cerebellum’s role in dystonia genesis remains unexamined, it will be difficult to significantly improve the current standards of dystonia treatment or to provide curative treatment.”

History
The Italian Bernardino Ramazzini provided one of the first descriptions of task-specific dystonia in 1713 in a book of occupational diseases, The Morbis Artificum. In chapter II of this book’s Supplementum, Ramazzini noted that “Scribes and Notaries” may develop “incessant movement of the hand, always in the same direction … the continuous and almost tonic strain on the muscles… that results in failure of power in the right hand.” A report from the British Civil Service also contained an early description of writer’s cramp. In 1864, Solly coined the term “scrivener’s palsy” for this affliction. These historical reports usually attributed the etiology of the motor abnormalities to overuse. Then, dystonia were reported in detail in 1911, when Hermann Oppenheim, Edward Flatau and Wladyslaw Sterling described some Jewish children affected by a syndrome that was retrospectively considered to represent familial cases of DYT1 dystonia. Some decades later, in 1975, the first international conference on dystonia was held in New York. It was then recognized that, in addition to severe generalized forms, the dystonia phenotype also encompasses poorly-progressive focal and segmental cases with onset in adulthood, such as blepharospasm, torticollis and writer’s cramp. These forms were previously considered independent disorders and were mainly classified among neuroses. A modern definition of dystonia was worded some years later, in 1984. During the following years it became evident that dystonia syndromes are numerous and diversified, new terminological descriptors (e.g., dystonia plus, heredodegenerative dystonias, etc.) and additional classification schemes were introduced. The clinical complexity of dystonia was then fully recognized.

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