Dystonia

The term dystonia is only very vaguely defined clinically. In fact, it describes several forms of diseases and complaints with different causes and also different clinical symptoms. Dystonia can be an independent disease, such as idiopathic torsional dystonia. This dystonia manifests itself in rotational movements primarily of the torso, neck and extremities, without any identifiable cause. However, dystonia often also describes a clinical syndrome as a result of other underlying diseases, such as symptomatic dystonia after childhood brain damage *.

The classification of dystonia is complex and very confusing even for experts. It is based both on the underlying causes as well as on clinical symptoms and the question which parts of the body are affected and to what extent. Basically, two forms of dystonia can be distinguished *:

1. Primary (idiopathic) dystonia
2. Secondary (symptomatic) dystonia

Primary dystonia occurs independently of an event or other disease. When its cause is unclear, it is called idiopathic dystonia.

Secondary dystonia results from an event or an underlying disease. The dystonia is then only a symptom of that condition. Examples include a lack of oxygen to the brain during birth, encephalitis, traumatic brain injury, or stroke.

Very important for the clinical dystonia classification is also the distribution pattern of involuntary movements. A distinction is made between the following types:

• Generalized dystonia
  Dystonia affects several segments or even non-contiguous areas of the body
• Segmental, multifocal dystonia
  Dystonia affects contiguous body segments (e.g., the entire arm, leg, trunk, neck, etc.).
• Focal dystonia
  A single part of the body is affected by dystonia. Examples of this are writer's cramp (graphospasm), eyelid spasm (blepharospasm), or spasmodic torticollis

Overall, idiopathic focal and segmental dystonias in adults account for the largest proportion of primary dystonia syndromes.

Due to the heterogeneity of what is called dystonia, it is difficult to come up with exact numbers. Estimates suggest a prevalence of 40 affected persons per 100,000 inhabitants, which corresponds to about 280,000 affected persons in Switzerland. The onset of the disease is usually between the ages of 30 and 50. Men and women are affected with equal frequency.

So far, there is no unified model that explains the different forms of dystonia. In recent years, a genetic cause has been found for a growing number of primary dystonias. This was first discovered for idiopathic torsional dystonia, a generalized dystonia (extending to several non-adjacent regions) with onset in childhood. The responsible gene DYT1 is detectable in affected individuals and directly heritable. The role and function of this gene in healthy humans is still the subject of active research.

On the other hand, in secondary dystonia, lesions are often observed in the area of the basal ganglia, a nuclear area in the depth of the cerebrum. The cause of these lesions may be circulatory disturbances, inflammatory diseases, or cerebral hemorrhages. Similar to Parkinson’s disease, dystonia is explained as a disturbance within the complex and finely tuned neuronal network within the basal ganglia, which play a central role in the control and regulation of motor activity.

Furthermore, it has been found that drugs that affect the metabolism of the neurotransmitter dopamine can trigger dystonia. This fits in with the fact that dopamine is an important neurotransmitter within the basal ganglia and has a decisive influence on information processing and can therefore also be causally involved in the development of symptoms.

Dystonia manifests itself in strong, persistent spasms of the skeletal muscles, which the affected person cannot control or influence by will. These contractions are often repetitive, which means that they repeat themselves in rapid sequences. The resulting abnormal postures, twisting movements and sometimes bizarre contortions of individual body parts are often accompanied by pain and severely restrict those affected in their everyday activities. The dystonic symptoms can be intensified by paying attention, emotional arousal and passive movements and subside with sleep and during anesthesia.

If left untreated, dystonia can increasingly lead to the death of muscle tissue, severe contractions, and skeletal deformities such as scoliosis, resulting in disability.

Frequently, patients with dystonia are observed to have an additional tremor. The tremor may be fine-beat (low-frequency) and manifest itself when the hands are actively held, or it may occur as a slower tremor in the dystonic part of the body. The dystonic tremor can sometimes precede the actual dystonia by years and is difficult to diagnose in these cases.

The diagnosis of a dystonic syndrome is made clinically, that is, based on specific questioning of the patient and clinical examination findings. Recognition of typical movement patterns caused by slow repetitive muscle contractions leading to abnormal postures is essential. Other additional neurological symptoms such as paralysis (paresis), abnormal reflexes due to damage of the pyramidal tract (pyramidal tract signs), disturbances of movement coordination (ataxia) or cognitive performance deficits exclude the diagnosis of idiopathic dystonia. Further diagnostic testing should include magnetic resonance imaging (MRI) of the skull to rule out a secondary form of dystonia. In certain cases, genetic testing is also performed.

A causal treatment is only possible in the rare hereditary disorder of L-dopa-sensitive dystonia, which is also known as Segawa syndrome. Since many primary forms of dystonia in childhood respond to dopamine, a drug trial with the drug L-dopa should be at the beginning of treatment in children. In adults, on the other hand, an often lengthy L-dopa therapy trial is hardly worthwhile.

Symptomatic treatment of dystonia is primarily based on the affected body regions. In focal dystonias such as writer's cramp or torticollis, local injections of botulinum toxin are usually the first choice of therapy to specifically relieve the muscular spasms.

A therapy-resistant dystonic tremor also responds to deep brain stimulation. However, the success rate, clinical effects, and long-term results are less successful than with an essential tremor *. The target in this case is the motor thalamus (VIM) or the posterior subthalamic area (PSA). A combination of GPi stimulation and VIM or PSA stimulation must be discussed in individual cases.

In principle, side effects are the same as with all stereotactic functional DBS procedures. Specific risks associated with GPi stimulation for the treatment of dystonia may include transient perceptions of "flashes of light" upon stimulation of the optic tract, muscular twitching, speech disorders (dysarthria), or sensory abnormalities. As a rule, however, these stimulation-induced side effects are reversible.

As with other diseases, the diagnosis of DBS is generally made on an interdisciplinary basis between neurologists and neurosurgeons. Extensive examinations, such as neurological examinations, neuropsychological tests, a psychiatric evaluation, and a surgical assessment are carried out in advance. This is to ensure that only patients with very good prospects of improving their symptoms are selected for the procedure. At Inselspital, patient cases are discussed individually by our interdisciplinary Movement Disorders Board in order to offer the best therapy options to each individual patient.