Dyskinesia

What is dyskinesia?

Among the disorders of a kinetic nature, dyskinesia undoubtedly plays a cardinal role: the term refers to some involuntary movements of the muscles, which are hyperkinetic in some cases and hypokinetic in others.

In all pathologies in which there is an involuntary and uncontrolled reduction or increase in voluntary movements or, again, an "evident muscular difficulty, one can correctly speak of dyskinesia.
The probability of onset of dyskinesias increases whenever there is damage or dysfunction of the CNS (central nervous system, which includes the spinal cord and brain), muscles or nerves. In other words, dyskinesia represents a "appreciable difficulty in controlling muscle movements.
The term dyskinesia, however, does not refer only to those disorders that fall within the neurological sphere (lack of mastery of the voluntary musculature), as it is also used in internal medicine to express the difficulty of managing the movement of some hollow organs or viscera.

Causes

It is not always easy and immediate to identify the attributable causes, given the vast differentiation of these kinetic disorders; in any case, among the etiopathological factors that most frequently generate dyskinesias: traumatic events, autoimmune diseases, ischemic pathologies of the cerebral circulation, infections of the CNS, disorders affecting peripheral nerves and genetic degenerative diseases or caused by the improper use of drugs (DIMD, English acronym for Drug-Induced Movement Disorders).

Dyskinesias and DIMD

By DIMD s "we mean a heterogeneous group of movement disorders induced by pharmacological specialties: this category deserves further study, as it hides a" wide diversification of the various types of dyskinesias. The DIMDs include: dystonia, akathisia and tardive dyskinesias (eg parkinsonism and stereotypies).
Dystonia represents those involuntary muscle contractions, protracted over time, characterized by repetitive and cadenced gestures: dystonia is a typical dyskinesia of the cranio-cervical areas.
Akathisia outlines a clinical profile characterized by a sort of internal tremor: the subject affected by akathisia tends to be restless and unable to stop or relax.

As regards tardive dyskinesias, the topic is more complex and delicate; the aforementioned condition refers to a paradigmatic collateral dyskinesia of the administration of antipsychotic - neuroleptic (with the exception of clozapine) and antiemetic substances. Typical of tardive dyskinesias are involuntary hyperkinetic movements , therefore not controlled, which heavily affect the neuromuscular function of each body site, despite the orofacial region being more affected (mouth, tongue, facial muscles). Tardive dyskinesias, also characterized by rigidity, muscle tension and bradykinesia difficulty in slowly controlling a voluntary movement), manifest themselves with stereotyped, frequent and rhythmic movements, such as movements of the fingers and toes, body fluctuations and stretching of the feet. Parkinsonism is also classified among the tardive dyskinesias: usually, the movements involuntary of this condition one onset 5-10 years after the start of drug treatment with levodopa.
When these hyperkinetic movements follow the interruption of drug therapy, we speak of tardive withdrawal dyskinesia.

Antipsychotics and dyskinesias

Following the description of these DIMDs, it is natural to ask what is the mechanism of action of these pharmacological substances, in relation to movement: why do neuroleptic-antipsychotic drugs generate these side effects?
Antipsychotic substances exert an anti-dopaminergic action: in other words, these drugs block the D2 receptor for dopamine, a well-known neurotransmitter synthesized by the body and involved in the cerebral mechanisms of movement and mood control. [Taken from www.dyskinesia. it]. In recent years, research aimed at improving the pharmacological profile has been encouraged: in this regard, new neuroleptic drugs have been formulated, known as atypical neuroleptics, able to exert the same pharmacological effects as the previous ones, with the advantage of significantly reducing the side effects on movement (dyskinesias), at the same dosage. However, it should be pointed out that at higher doses, even new neuroleptics can cause dyskinesias.

General classification

The kinetic alterations are not attributable solely to the administration of neuroleptic substances; depending on the location of the deficit and its characteristics, dyskinesias are categorized into:

Athetosis: involuntary movements are particularly slow, albeit continuous. Typical dyskinesia involving hands and feet: the affected patient tends to practice twisting movements in the extremities.
Korea: movements appear rapid, continuous and uncontrolled. They can involve only a few muscles or the whole body.
Cramps: Cramps are also part of dyskinesias. They are involuntary and painful movements, the cause of which lies above all in excessive muscular effort and loss of electrolytes.
Dystonia: it expresses an abnormal posture assumed by the body, given by the involuntary constriction of some muscle bundles.
Hemiballism (or more simply ballism): this dyskinesia is characterized by particularly violent movements of the body, which manifest a sort of involuntary "rush".
Myoclonus: Typically, we speak of nocturnal myoclonus, as they occur most often during sleep. These are short and temporary involuntary movements: in some cases they do not constitute an alarming condition, in others, however, they represent an alarm bell for degenerative diseases.
Synkinesia: complex dyskinesia, in which an involuntary movement is made with one limb, when instead the movement is being made in the other limb.
Spasms: typical dyskinesia caused by hypocalcemia and tetanus
Tics: Tics are one of the stereotypical dyskinesias, whose repeated, identical and rhythmic movements have a psychogenic nature.
Tremors: some authors do not include tremors among dyskinesias: the CIOMS (Council for International Organizations of Medical Sciences) excludes muscle-type tremors from dyskinesias, since they are given by "lesions affecting the cells of the anterior horns or the peripheral nerve " therefore not due to extrapyramidal deficits. [www.farmacovigilanza.org/]. However, for other authors, however, tremors must be categorized as dyskinesias, since they are also involuntary movements of the muscles in this case. Tremors represent rhythmic muscle oscillations not predicted by the CNS, generated by antagonistic muscle bundles. Senile tremor, essential tremor and cerebellar tremor are distinguished.

Internal anatomical movements

As mentioned in the introduction, dyskinesias do not only refer to clonic outbursts; in internal medicine, in fact, dyskinesias are attributed to movements of internal organs or viscera. Internal dyskinesias are also classified; Here are some examples:

uterine dyskinesia: the involuntary and spastic movement of the uterine muscles could have repercussions during childbirth;
biliary dyskinesia: the alteration of contractile movements and the speed of emptying of the bile ducts and gallbladder could generate digestive disorders;
myocardial dyskinesia: impaired cardiac motion;
primary ciliary dyskinesia: alteration of ciliary function of the respiratory mucosa;
dyskinesias of the upper esophageal sphincter (or idiopathic achalasia): the lack of incomplete relaxation of the esophageal sphincter when swallowing generates a sensitive status hypertensive. [adapted from Surgery. Vol 1-2 by R. Dionigi].

In any case, internal dyskinesias are rather painful and could ideally affect all organs: they are generally due to an uncoordination of the contractile function of the muscular layer of the organ concerned, regardless of clearly detectable pathologies.