Dystonias are movement disorders in which sustained muscle contractions cause twisting and repetitive movements or abnormal postures. The movements, which are involuntary and sometimes painful.
Focal dystonia refers to dystonia that is localized to a specific part of the body.
Types of Focal Dystonia
Focal dystonia is often classified by the part of the body or muscle group affected.
Cervical dystonia (also called "spasmodic torticollis", "torticollis", or "wryneck") is the most common type of focal dystonia. It is the third most common movement disorder, after Parkinson's disease and tremor.
The muscles in the neck that control the position of the head do no move properly, causing the head to twist and turn to one side. The head may also be pulled forward or backward. Cervical dystonia can occur at any age, but it arises most commonly in people 30 to 50 years old. The symptoms begin slowly and worsen until they reach a steady state. About 10-20% of people with cervical dystonia experience a spontaneous remission, but it may not be lasting.
Benign Essential Blepharospasm
Benign essential blepharospasm (BEB) is the second most common focal dystonia. It results in involuntary, forced closure of the eyelids. Uncontrollable blinking is often the first symptom to appear. It may affect only one eye at first, but both eyes usually are involved. The spasms of the eyelids may seriously impair vision. The condition begins gradually with increased frequency of eye blinking often associated with eye irritation. Other symptoms may include involuntary winking or squinting of one or both eyes, increasing difficulty in keeping the eyes open, and light sensitivity. Generally, the spasms occur during the day, disappear in sleep, and reappear after waking. As the condition progresses, the spasms may intensify, forcing the eyelids to remain closed for long periods of time, and thereby causing substantial visual disturbance or functional blindness. With botulinum toxin treatment most individuals with benign essential blepharospasms have substantial relief of symptoms. Although some may experience side effects such as drooping eyelids, blurred or double vision, and eye dryness, these side effects are usually only temporary.
Oromandibular dystonia affects the muscles of the jaw, lips, and tongue. The jaw may be pulled either open or shut, and speech and swallowing can be difficult.
Spasmodic dysphonia (also called "spastic dysphonia" or "laryngeal dystonia") involves the muscles of the throat that control speech. It results in strained and difficult speaking or breathy and effortful speech.
Hemifacial Spasm is characterized by frequent involuntary contractions of the muscles on one side of the face. The first symptom is usually an intermittent twitching of the eyelid muscle that can lead to forced closure of the eye. The spasm may then gradually spread to involve the muscles of the lower face, which may cause the mouth to be pulled to one side. Eventually the spasms involve all of the muscles on one side of the face almost continuously. The disorder occurs in both men and women, although it more frequently affects middle-aged or elderly women. The condition may be caused by a facial nerve injury or a tumor, or it may have no apparent cause. Very commonly, hemifacial spasm is caused by a blood vessel pressing on the facial nerve.
Writer's cramp is a dystonia that affects the muscles of the hand and sometimes the forearm, and only occurs during handwriting. It is also referred to as "typist's cramp", "pianist's cramp", and "musician's cramp".
Other forms of focal dystonia
Meige's syndrome is the name of a movement disorder with blepharospasm and oromandibular dystonia. Spasmodic dysphonia may also occur in people with Meige's syndrome.
Cause of Focal Dystonia
The cause of focal dystonia is not fully understood, but appears to be due to an abnormality in an area of the brain called the basal ganglia where some of the messages that initiate muscle contractions are processed.
Focal Dystonia Treatment
No single treatment has been found to be universally effective for focal dystonias. Instead, physicians use a variety of therapies aimed at reducing or eliminating muscle spasms and pain.
Medications, such as clonazepam, diazepam (Valium®) or tizanidine (Zanaflex®) may be attempted to provide partial relaxation of the muscle or pain relief. Unfortunately, oral medications alone rarely provide sufficient relief of symptoms.
Botulinum Toxin for Focal Dystonia
Botulinum toxin injections into affected muscles have been shown to be effective for treating focal dystonias. The toxin stops muscle spasms by blocking release ofacetylcholine, an excitatory neurotransmitter. The effect lasts for 3-6 months before the injections have to be repeated.
First used to treat blepharospasm, botulinum toxin injections have gained wider acceptance among physicians for treating other focal dystonias, particularly cervical dystonia.
Botulinum toxin is readily available in two commercial forms; Botox® and Dysport®. These injections have the advantage of being readily available and the effects are not permanent. There is a risk of temporary paralysis of the muscles being injected or the leaking of the toxin into adjacent muscle groups causing weakness or paralysis in them. The injections have to be repeated as the effects wear off and around 15% of recipients will develop immunity to the toxin (Antibodies develop against the toxin). Those that develop resistance to one type of botulinum toxin may be able to use another.
Surgery for focal dystonia
Surgery may be recommended for some patients when medication is unsuccessful or the side effects are too severe. Surgically cutting or removing the nerves to the affected muscles has helped some focal dystonias, including blepharospasm, spasmodic dysphonia and cervical dystonia. The benefits of these operations, however, can be short-lived. They also carry the risk of disfigurement, can be unpredictable, and are irreversible.
Other treatments for focal dystonia.
Some patients with spasmodic dysphonia may benefit from treatment by a speech-language pathologist. Physical therapy, splinting, stress management, and biofeedback may also help some people with certain forms of focal dystonia.
Reference: National Institute of Neurological Diseases and Stroke (NINDS)