Dystonia

Types of dystonia by location

Dystonia can have any body distribution. The most frequent are:

1.- Focal Dystonia: It affects only one part of the body and is more frequent in adults.

• The most frequent focal dystonia in adults is cervical dystonia (torticollis), which is characterized by cephalic rotation to one side, in the axial plane. In many cases it starts as a cephalic tremor. Unlike other focal dystonias, it is accompanied by pain in a significant percentage of cases. In almost all cases there is an improvement in dystonia with the performance of an antagonistic gesture. The association with tremor (hands or cephalic) is frequent. 
• Blepharospasm is a focal dystonia characterized by intermittent or sustained contraction of the orbicularis oculi muscles that causes in many cases an involuntary and sustained closure of the eyes. Light and wind are factors that aggravate the symptoms. Generally, the spasms are not painful but there may be a feeling of dryness in the eye. In some cases the blepharospasm is associated with involuntary movements of the oromandibular musculature (Meige's syndrome) that can interfere with the articulation of the language.
• Laryngeal dystonia. It is a form of dystonia that appears exclusively when speaking in the usual tone of conversations and is produced by an abnormal contraction of the muscles that regulate the opening and closing of the vocal cords. A characteristic feature is that subjects can sing or speak in a low tone without difficulty.
• Occupational dystonia. They occur only when performing a specific motor activity. The scribe's cramp is the most frequent occupational dystonia, affecting the hand and forearm muscles and appearing exclusively during writing, while the rest of manual activities are not impeded. Other occupational dystonias include musician's, tennis player's or golfer's dystonia.

2.- Generalized dystonia. It is more frequent in children. It tends to start in the legs and progresses upwards to the trunk, which tends to twist, and to other regions of the body until it becomes generalized. It is also called torsion dystonia.

What are the causes of dystonia?

Dystonia is due to a functional or structural alteration of the central nervous system that causes the malfunctioning of the brain circuits that control movement. We can differentiate them in the primary and secondary dystonias:

The primary or idiopathic ones are those genetic hereditary or idiopathic forms in which another disease or responsible agent has not been identified. There have been identified a number of genes associated to different forms of dystonia presentation.

In the literature these forms of dystonia are described as DYT followed by a number; of which there are at least 27 different forms identified (DYT-1 to DYT27). Some of them manifest with isolated dystonia and in other cases there is a combination of dystonia with another type of movement disorder (combined dystonia).

To this group of dystonias belong also the paroxysmal dystonias in which dystonia appears episodically, lasts a certain time (from minutes to hours) and patients are asymptomatic between two consecutive episodes. In some cases there are precipitating factors of dystonia such as exercise, fasting, or the intake of tea or coffee.

Secondary dystonias are those whose cause is related to other factors such as drugs, focal structural lesions of the brain, metabolic alterations (consider alteration of the metabolism of copper, such as Wilson's disease, or of iron and alteration of the metabolism of dopamine), autoimmune diseases (such as encephalitis or multiple sclerosis) or degenerative diseases such as Huntingon's disease or parkinsonism by mutation in PARK2.