Dystonia is a movement disorder characterized by involuntary muscle contractions, which can be sustained or spasmodic, causing abnormal postures in the subject.
The dystonia belongs to a group of neurological diseases called disorders movement, including Parkinson’s disease, the tics, and chorea. It is characterized by presenting involuntary contractions of agonist and antagonist muscles simultaneously, which can be sustained or spasmodic, causing abnormal postures of one or multiple regions of the subject’s body.
Typically, dystonic movements repeat themselves in the same pattern, worsen with action, and disappear during sleep.
Depending on its distribution, dystonia can be focal (affects a single region of the body) – usually 3 out of 4 cases -, segmental (affects two adjacent areas), multifocal (affects two or more non-adjacent regions ), hemidystonia (affects either the right half or the left half of the body) or generalized (affects more than two adjacent parts) – approximately 1.3% of dystonias.
The prevalence in Spain is 3.4 cases per 100,000 in generalized forms and 30 per 100,000 in focal ones. In Mexico, for example, the number of people affected is estimated to be one in every 3,000 people. These are approximate data since it is estimated that much focal dystonia with few symptoms is not diagnosed.
Dystonia is estimated to be the third common movement disorder after Parkinson’s disease and it is 3 most common type of movement disorder in childhood, behind spasticity and tics. Some population groups seem especially sensitive to suffering from dystonia, such as musicians –certain studies indicate that 10% of these professionals suffer from it– or golfers –35% of these athletes see their careers limited by this problem.
One of the biggest problems that this condition raises is the difficulty in diagnosing it. Approximately 40% of those affected have been misdiagnosed by confusing the origin of the causes with emotional or psychological reasons, which only occurs in one of each 20 cases.
The dystonia is due to dysfunction of the motor control circuit regulated by the basal ganglia (nuclei of nerve cell bodies that lie near the brain’s base). It has been suggested that dystonia results from a lack of inhibition or increased activation by these nuclei on the cortical sensory-motor area, causing muscle hyperexcitability.
According to the causal criterion, they can be classified into two large groups:
- Primary or idiopathic: hereditary or sporadic cases not secondary to other diseases or known causative agents.
- Secondary: there is a previous disease or agent (for example, some drugs) that causes dystonia.
Types of dystonias
font-weight: 400;”>Let’s see the types of dystonias that exist within these two large groups:
Sporadic: they typically appear in adulthood and follow a fluctuating course at the beginning. In most cases, they are focal, and adjacent regions are only affected in a small percentage. The most frequent forms are:
- Cervical dystonia or spasmodic torticollis: abnormal neck posture that may be accompanied by tremor or pain.
- Blepharospasm: intermittent contraction of the orbicularis oculi muscles. If the contractions are very prolonged, patients can become “functionally blind.”
- Laryngeal dystonia: a broken voice or a continuous lack of voice appears due to the vocal cords’ involvement.
- Occupational dystonias: appear exclusively when performing a specific activity. The best-known case is the “scribe’s dystonia,” which appears only when the subject writes, forcing him to abandon the action. Other very common dystonias are professional ones, such as the musician’s dystonia.
Hereditary dystonias: a heterogeneous group with a genetic substrate. The known genes involved are called “DYT.” The most common is dystonia with a DYT1 gene mutation, but there are many others (DYT2, DYT6), and all of them are rare diseases.
- Generalized idiopathic or Oppenheim dystonia: The DYT1 gene is altered and is transmitted in an autosomal dominant manner. It begins in childhood or youth, generally affecting a limb or trunk. The prognosis is variable. It can remain relatively stable or progress to generalize and become disabling. It is a rare disease, more prevalent in Ashkenazi Jews.