What is Dystonia?
Dystonia is a neurological movement disorder characterized by involuntary muscle contractions, which force certain parts of the body into abnormal, sometimes painful, movements or postures.
Dystonia can affect any part of the body including the arms and legs, trunk, neck, eyelids, face, or vocal cords.
If dystonia causes any type of impairment, it is because muscle contractions interfere with normal function. Features such as cognition, strength, and the senses, including vision and hearing are normal. While dystonia is not fatal, it is a chronic disorder and prognosis is difficult to predict.
It is the third most common movement disorder after Parkinson's Disease and Tremor, affecting more than 300,000 people in North America. Dystonia does not discriminate - affecting all races and ethnic groups.
Dystonia is classified in three ways: age of onset, body distribution of symptoms, and etiology or cause of the disorder.
Age of Onset
The symptoms of dystonia may begin during childhood (early-onset), in adolescence, or during adulthood.
Dystonia with either childhood-onset and adolescent-onset (<28) is usually associated with an inherited defect in a gene and begins in early childhood after a period of normal physical development. It often initially involves a limb, in particular the foot and leg. These symptoms may initially appear only during activities such as running or walking and may spread to involve other body areas.
The appearance of symptoms in adult-onset dystonia (>28) typically starts between ages 30 to 50 following decades of normal physical function. The symptoms tend to remain focal, affecting one particular part of the body.
Age of onset tends to be the best factor in determining the chance of progression. Generally, the earlier the onset of symptoms, the greater the chances are of progression of symptoms with age.
Body Distribution of Symptoms
Any body region may be affected by dystonia. Classification is done by the number and specific areas of the body that are affected:
- Focal - Most frequent type of dystonia; affects one single area of the body
- Segmental - Affects at least two or more areas of the body that are adjacent.
- Multi-focal - Appears in two or more areas of the body that are not adjacent
- Generalized - Involves several body areas on both sides of the body
- Hemi-dystonia - Affects either the left or the right side of the body.
Etiology or cause of the dystonia
The classification of dystonia by causes uses broad categories: primary and secondary dystonia.
Primary dystonia is defined by the existence of dystonia alone without any underlying disorder. This category includes hereditary ("classic") and sporadic ("variant") forms of dystonia.
Early-onset generalized dystonia associated with the DYT1 gene is considered to be a classic form of primary form of dystonia because the movements and postures constitute the sole neurological abnormality.
Variant forms of dystonia are marked by atypical clinical features and may be etiologically distinct from the classic form. Dopa-Responsive, Paroxysmal, X-Linked Dystonia-Parkinsonian, Myoclonic, and Rapid-Onset Dystonia-Parkinsonian are all considered variant forms.
Secondary forms of dystonia arise from and can be attributed to numerous causes, such as birth injury, trauma, toxins, or stroke. Secondary dystonia can be symptomatic, and can also occur in association with other disorders such as Wilson's disease.
Primary dystonia is believed to be due to abnormal functioning of the basal ganglia which are deep brain structures involved with the control of movement. The basal ganglia assists in initiating and regulating movement. What goes wrong in the basal ganglia is still unknown. An imbalance of dopamine, a neurotransmitter in the basal ganglia, may underlie several different forms of dystonia, but much more research needs to be done for a better understanding of the brain mechanisms involved with dystonia.
Secondary forms of dystonia arise from and can be attributed to numerous causes, such as birth injury, trauma, toxins, or stroke. Secondary dystonia can be symptomatic and can also occur in association with other disorders such as Wilson's disease. When dystonia is secondary to certain injuries or small strokes, we often find lesions (areas of damage) in the putamen, one nucleus in the basal ganglia, as well as in certain nearby structures. Even though we can see no microscopic abnormalities of the brain in the great majority of cases of dystonia, including those with generalized dystonia, the evidence is so clear in the secondary dystonias that we believe the same part of the brain is involved in all types.
How does dystonia work in the brain?
Dystonia is a disorder that has to do with the way we move. The control of our movements is very complicated and involves many areas in the brain. The area of the brain that is involved in dystonia is called the basal ganglia. The basal ganglia is a deep region of the brain that controls the speed of movement and prevents unwanted movements.
If there is a small change in the way the basal ganglia works, it can cause movements to occur even if you don't want them to. This small change is not found by medical tests or pictures of the brain on an MRI scan. Even if this deep area of the brain is not working the right way and dystonia occurs, the areas of the brain that have to do with thinking and learning work normally. Once researchers understand what the problem is in this part of the brain, they will be able to come up with ways to allow persons with dystonia to control these unwanted movements.
Can dystonia come about overnight? Are there any warning signs?
Dystonia generally develops gradually. Occasionally the dystonia may occur suddenly, as in the acute dystonic reactions related to the administration of antipsychotic drugs. These attacks most commonly affect the head and neck muscles and are usually transient and readily treatable.
Some clinical features may precede the full clinical presentation of dystonia. Eye irritation, excessive sensitivity to bright light, and increased blinking may precede blepharospasm. Subtle facial or jaw spasms, difficulty chewing, changes in the cadence or pitch of speech may suggest early face, jaw, or voice dystonia. Mild jerky head movements, stiff neck, or local neck discomfort may occur in early torticollis. Cramping or fatiguing of the hands during writing, other manual activities, or walking may suggest limb dystonia. Sometimes a local dystonia may seem to arise directly following injury to a local body region.
Can dystonia affect muscles such as the heart or diaphragm?
Dystonia can affect breathing in several ways. Severe neck dystonia can cause difficulty breathing when the upper airway is partially closed off. Dystonia involving the vocal cords can potentially cause shortness of breath when the vocal cords close tight, but in general the tightness is present primarily when speaking. The act of breathing involves muscles between the ribs and a large muscle called the diaphragm. Dystonia can cause stiffness in the muscles between the ribs and can cause a sensation or shortness of breath. Occasionally, the diaphragm can also be affected. Finally, when a person with dystonia has involvement of the spine, twisting of the torso can limit how much the lungs can expand when breathing, and this can potentially cause shortness of breath. The heart muscle is not affected by dystonia.
Can you die from dystonia?
In the overwhelming majority of people with dystonia, it does not shorten life expectancy or result in death. In very severe, generalized dystonia, affecting all body areas, there can be problems that may arise secondary to the dystonia which can cause medical illnesses. However, these instances are quite rare and usually treatable.
Can exposure to toxins or specific chemicals cause dystonia?
The answer to this question is clearly yes. This is distinctly different from widespread environmental exposures to which large numbers of dystonic patients could be exposed. A number of uncommon toxins are capable of causing brain damage centered in the motor control region known as the basal ganglia. Dystonia may be one prominent feature experienced by patients with these exposures, but it is extremely uncommon for "isolated dystonia" to be seen in such patients. In other words, the vast majority of patients exposed to toxins (for example, manganeses) have additional neurological problems associated with the dystonia. Possibly the most common feature in such patients is the presence of a Parkinson's disease-like state.
A large number of drugs are capable of causing dystonia. In most cases, the dystonia is transient but in some patients exposed to neuroleptics, such as Haldol, the dystonia may be persistent. This disorder, known as "tardive dystonia," in contrast to dystonia associated with other neurotoxins, commonly manifests isolated dystonia without additional neurological problems.
If you are not born with dystonia, what causes it to manifest itself later in life?
It is quite rare to see someone "born" with dystonia, manifesting symptoms at the time of birth. Childhood-onset dystonia associated with the inherited form of dystonia begins in early childhood after a period of normal physical development and often initially involves the leg and foot. In adult-onset dystonia, the onset is typically in the 40's following decades of normal physical function. The reason for the appearance of dystonia after initial normal development and function is not known. It is thought that in some people there are external factors which may trigger the dystonia, but specific triggers have not yet been identified.
Can dystonia be caused by a injury?
To date, there is some evidence to support a role of trauma including injury to the head or other body parts.It makes sense that if these factors can influence genetic forms of dystonia, they may also be important to other forms of primary dystonia where there is little or no genetic influence. Studies of these questions require accurate and detailed evaluations of the past histories of large numbers of patients as well as unaffected individuals or "controls." One reason for pursuing these issues is that it is well established that trauma does occasionally result in some forms of well-established "secondary" dystonia.
For example, closed head injury can sometimes result in severe dystonia. Typically in these cases, the injury has been severe enough to result in damage to the basal ganglia, which can be visualized on brain imaging studies. Direct injury to a limb may also result in severe dystonic postures. The mechanisms underlying this "peripheral injury-induced dystonia" are poorly understood.
It appears from the literature that people who are carriers of the gene for dystonia may be more likely to have trauma as a triggering factor for the development of dystonia. When people have an injury and then develop dystonia in that body part, you are tempted to say, "There must be some relationship between the trauma and the dystonia." There are legal aspects of trauma-induced dystonia that have to be dealt with as well. It's a gray area at this point. It may be that there is a triggering factor, but we're really not clear as to why some people who have the gene manifest the symptoms and some do not.
Is dystonia a sensory disorder?
On first appearance, dystonia is a movement disorder. It is characterized by abnormal postures and movements. Sensation seems normal. There are clues, however, that sensory function may not be completely normal and that sensory features are important. Since the sensory system is an important influence on the motor system, abnormalities of the sensory system could be relevant in causing motor dysfunction.
Sensory tricks can relieve a dystonic spasm. The most commonly noted is the "geste" in spasmodic torticollis where, for example, a finger placed lightly on the face will neutralize the spasm. Such tricks are seen in all forms of dystonia. Pressure on the eyelids might improve blepharospasm, a toothpick in the mouth might relieve tongue dystonia, and sensation applied to parts of the arm might improve a writer's cramp.
On the other hand, sensory stimulation might trigger dystonia. This might be called a reverse "geste." Examples include a tart taste producing tongue dystonia or a loud noise producing spasmodic torticollis.
Sensory symptoms may well precede the appearance of dystonia. Common examples would be a gritty sensation in the eye preceding blepharospasm and irritation of the throat preceding spasmodic dysphonia. Photophobia is an example of distorted sensation.
Abnormal sensory input might well be a trigger for dystonia. Trauma to a body part is often a precedent to dystonia of that part. A blow to the head might precede torticollis, irritations of the eye are common in blepharospasm, and a deep cut of the hand might occur just before writer's cramp develops.
There may be an important problem with the processing of muscle spindle input. In patients with hand cramps, vibration can induce the patient's dystonia. Cutaneous input similar to that which produces the sensory trick can reverse the vibration-induced dystonia. Conversely, both action-induced and vibration-induced dystonia can be improved with lidocaine block of the muscle, which will reduce sensory input.
The brain response to somatosensory input is abnormal in dystonia. This can be demonstrated with PET studies and evoked potential studies using EEG. In addition, studies of sensory receptive fields of neurons in the thalamus in humans with dystonia show expanded regions where cells all respond to the same passive movement. Mapping of the location of cortical sensory areas of the different fingers is abnormal in dystonia, and this is potentially consistent with the idea that there is abnormal cortical plasticity.
Lastly, there is some evidence that there might, in fact, be subtle abnormalities of sensation in patients with dystonia. The best evidence is for an abnormality of proprioception, the sense of movement of body parts.
How do doctors diagnose dystonia?
At this time, there is no test to confirm diagnosis of dystonia. Instead, the diagnosis of dystonia rests solely on the information from the affected individual and the physical and neurological examination. In order to correctly diagnose dystonia, therefore, doctors must be able to recognize the physical signs and be familiar with the symptoms. In certain instances, further tests may be ordered to be sure that there are not other problems associated with dystonia, but in many cases these tests will be normal.
When dystonia begins, often it may change significantly with different actions. For example, dystonia of the foot may occur when walking forward but disappear completely when walking backward or while sitting in a chair. In some people, dystonia involving the hand will only happen when writing and not with any other activity. The changeable nature of dystonia has led some physicians and even some dystonia-affected persons wondering if the cause of dystonia may be "all in their head." This is not true. Dystonia is a neurologic condition that is not the result of a psychiatric problem. In order to diagnose dystonia, a doctor who is familiar with the disorder is necessary.
If dystonia is diagnosed it is important to remember that features such as cognition, strength, and the senses, including vision and hearing, are normal.
Is a normal MRI typical analysis for the diagnosis of dystonia? Yes, unless the dystonia is the result of some other problem. If it's idiopathic dystonia, the MRI is normal. Blood tests are normal, and electrophysiology is, to a large degree, also normal. As far as secondary dystonia, it depends upon the reason for having it. Typically, if we do a large evaluation of someone with dystonia, that means we think there is something atypical about the way the person looks that says to us, "We'd better make sure that there is nothing else going on."
Why do some patients have one dystonic symptom while others develop several?
Dystonia is highly variable in its manifestations, and this observation is one of the reasons that dystonia has been misunderstood for so long. Whereas one patient complains of painful cramps, another may find that the foot turns in unexpectedly during walking, but there is no pain or cramp at all. Scientists believe that the body area involved is determined by alteration in specific brain regions.
For example, in patients with dystonia on the left side of the body only, the chemical abnormality is thought to be predominantly or exclusively restricted to the right side of the brain. Further research is needed to determine exactly what portions of the brain relate to specific dystonic symptoms. One of the reasons that autopsy research is so important is the need to study individual symptoms and relate them to chemical and microscopic changes that occur in highly specific brain areas. Researchers hope that such efforts will lead to a clear understanding of the basis of dystonia and help scientists in their quest for treatment and cure.
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