Dystonia

Introduction

Dystonia is defined as involuntary, sustained and often repetitive muscle contractions of opposing muscles resulting in twisting or spasmodic movements or abnormal postures.

We don’t know exactly what causes Dystonia. Researchers believe Dystonia is due to abnormal functioning of the basal ganglia, which are deep brain structures involved with the control of movement. The basal ganglia assist in initiating and regulating movement. What goes wrong in the basal ganglia is still unknown. Lesions or alterations in the neurochemistry of basal ganglia lead to Thalamo-frontal disinhibition leading to dystonia. Some dystonias are inherited, some result from drug-induced effects, and some result from brain injuries. Dystonia does not discriminate anyone, regardless of race, age, or ethnicity. It is the third most common movement disorder after Parkinson’s disease and Tremor, affecting an estimated 300,000 persons in North America. (Epidemiological data for India is not available)

Types

Dystonia is classified as primary or idiopathic (no known organic lesion), secondary when some known insult occurred to the basal ganglia (trauma, toxins, drugs, neoplasm, infarction, or other organic causes); or classified by the body region involved.

Generalized dystonia (or idiopathic torsion dystonia) affects a wide range of body areas. It usually occurs in childhood (especially in early teen years), and often affects the limbs and feet.

Generalised Dystonia

Primary Generalised Dystonia is also known as Dystonia Musculorum Deformance (DMD). Most cases commence in childhood (age 0 to 13 years), though in some it may not appear till the teen years (age 13 to 20 years); adult onset is rare. Primary dystonia typically begins as a focal disturbance that progress either inexorably until it involves both sides of the body and leads to the patient’s death from respiratory difficulties as a result of truncal involvement or up to a point after which it becomes static. It is our observation that younger the age of onset, longer and more extensive the progress and vice versa, a conclusion also reached by other workers.

The various motor abnormalities in primary dystonia consist of phasic and/or tonic elements. Depending on the distribution of abnormal movements, primary dystonia may be described as generalised, hemi-dystonic, segmental or focal; multi-focal primary dystonia, which affects two or more disjunct body sides, also occurs. The common treatment for dystonia consists of drugs like Levodopa, Trihexphenidyl Hydrochloride and Tetrabenzine. The role of surgery in dystonia is limited to patients who have failed to respond after certain time of medical treatment. Proper case selection is very important in achieving good surgical outcome. Patients who have primary dystonia or familial dystonia secondary to genetic abnormalities such as DYT-1 gene abnormality are the candidates most suitable for functional neurosurgical procedures.

Secondary dystonia occurs due to variety of causes, including trauma, metabolic dysfunction, brain iron deposition (PKAN), infection, drug induced (tardive dyskinesias) etc. In several cases the cause may not be even known. Secondary dystonia are more resistant to treatment and may be more disabling. The diagnosis is established by a careful history and various investigations appropriate to each individual capacity.

Spasmodic Torticollis

Spasmodic torticollis is an adult onset focal or segmental dystonia. It is characterised by stereotype posture having a variable combination of neck flexion, extension, rotation and tilting. Each patient has a characteristic dystonic posturing. This dystonic posture is present at rest, worsen with action or stress, and improve or resolve completely during sleep. It is most commonly observed, in mid-adult life with the big incidence being between ages of 30 and 40 years. Initially it begins with a feel of tension in the neck muscles for months before the manifestation of dystonia. This is followed by intermittent posturing of the neck with head turning. Over a period of time this becomes constant and fixed, only abating during sleep. Symptoms may progress rapidly over several weeks or gradually over several years until a plateau is typically reached 3 to 5 years after the initial manifestation. Though temporary, spontaneous remission have been known, permanent remission is almost unusual. The non-operative treatment for spasmodic torticollis includes physiotherapy, cervical brace and anticholinergics like Trihexphenidyl Hydrochloride, Anti-depressants, and muscle relaxants. The most therapeutic intervention is either botulinum toxin injection or surgery. Botulinum toxin injection is given in the neck muscles to denervate the select group of muscles to relieve muscle spasm. However this relief is temporary and recurrence is noted after three months and injection has to be repeated.

Other focal dystonias affect specific body parts, but sometimes patients may suffer from more than one type of focal dystonia. These typically attack at mid life (40s to 50s).

Common focal dystonias are the following :

  • Spasmodic Torticollis (or cervical dystonia) affects muscles in neck, head, and spine that  cause the head to turn to one side.
  • Blepharospasm causes involuntary contraction of the eyelids holding them closed for indefinite periods.
  • Oromandibular dystonia affects jaw, lips, or tongue causing the jaw to be held open or clamped shut.
  • Orofacial-buccal dystonia (Meige’s or Brughel’s syndrome) a combination of blepharospasm and oromandibular dystonia.
  • Spasmodic dysphonia affects muscles that control the vocal cords causing halting, strained, or a breathless whisper voice.
  • Writer’s cramp (or occupational dystonia)  symptoms are triggered when the sufferer attempts to write or perform other fine hand functions, such as playing a musical instrument.

Treatment

Dystonia is treated by a variety of medications designed to reduce muscle spasms. In a few cases, specific surgery may be needed.Focaldystonias can be treated with Botulinum Toxin Type A. Botulinum toxin is produced by a bacterium called Clostridium botulinum, which is the bacteria that cause botulism. Botulinum toxin is injected in extremely small amounts directly into affected muscles to “weaken” the muscle or to actually “block” nerve signals telling the muscle to contract. The Botulinum toxin has a relatively short life span (from weeks to several months) as new nerve endings grow, at this stage the injections have to be repeated. It sometimes takes anywhere from 5-10 days for Botulinum toxin to begin affecting the muscles. Treatment for dystonia is designed to help lessen the symptoms of spasms, pain, and disturbed postures and functions. Most therapies are symptomatic, attempting to cover up or release the dystonic spasms. No single strategy will be appropriate for every case. The approach for treatment of dystonia may be three tiered: oral medications, botulinum toxin injections, and surgery. These therapies may be used alone or in combination.

Surgery may be considered when patients are no longer receptive to other treatments. It is most effective in patients who are suffering from idiopathic primary generalized dystonia and spasmodic Torticollis. Surgery is undertaken to interrupt, at various levels of the nervous system, the pathways responsible for the abnormal movements for e.g. dorsal root rhizotomies for patients suffering from spasmodic Torticollis. Some operations intentionally damage small regions of the thalamus (thalamotomy), globuspallidus(pallidotomy), or other deep centers in the brain. Recently, chronic deep brain stimulation (DBS) has been tried with some success. Other surgical approaches include cutting nerves going to the nerve roots deep in the neck close to the spinal cord (anterior cervical rhizotomy) or removing the nerves at the point they enter the contracting muscles (selective peripheral denervation).

In patients with unilateral dystonia, pallidotomy or pallidal stimulation can be performed. However, in patients with bilateral generalised dystonia with truncal involvement, deep brain stimulation of the globuspalliduminternus is the surgery of choice. The results of deep brain stimulation for dystonia are not apparent in the immediate post-operative period. It takes few months for the benefit of this surgery to be realized after careful programming and drug adjustments. However the advantage of deep brain stimulation surgery over lesional surgery is that the titration of the the Surgery has a definite role in the treatment of spasmodic torticollis. Surgery is aimed at selectively denervating the muscles, which are under tonic contraction. This selective denervation is done by exposing the dorsal nerve roots just outside the spinal canal from C1 to C6. With the help of electro-myographic studies and electrical stimulation during surgery the incriminated muscles are selectively denervated. The denervation is extended to avulsion of the nerves of the involved muscles, to prevent any recurrence. In one of the large series reported in literature it has been found that the results were good to excellent in nearly 88% of the patients out of 460 cases.