The thalamus is a brain structure that serves as a crossing point for multiple neuronal pathways (it is a “relay center”). His injury causes the thalamic syndrome, a clinical picture that triggers various symptoms, with predominance of thalamic pain.
Here we will know in detail the causes of this syndrome, as well as its symptoms and possible treatments.
The thalamus is a cerebral structure; it is a central gray nucleus of the base that serves as a cross-linking point for multiple neuronal pathways. It is an even structure, located on both sides of the third ventricle. It occupies approximately 80% of the diencephalon and is divided into four large sections (anterior, medial, lateral and posterior), in turn divided into several nuclei.
All sensory and sensory pathways that arise in the spinal cord, brainstem and hypothalamus, converge in the thalamus, where they relay (it is a “relay center”). In addition, the different coordination pathways of the extrapyramidal system, vestibular nuclei, cerebellum, striated nuclei and cerebral cortex are added.
Thalamic syndrome: characteristics
The thalamic syndrome, also known as Déjerine-Roussy syndrome, is characterized by the following symptoms: mild transient hemiparesis, hemicoreoathetosis, hemihypoestesia, hyperalgesia, allodynia and hemiataxia with astereognosia of variable intensity. This syndrome presents with lesions of the posterior nuclei of the thalamus.
The clinical manifestations produced by thalamic lesions are very diverse (since they encompass many pathways), poorly systematized, relatively infrequent and little known by the clinician, although we can specify them, as we will see later.
This syndrome was first described in early 1903, when Jules Joseph Dejerine and Gustave Roussy studied clinical and pathological facts of thalamic syndrome. His initial description of the thalamic syndrome continues to this day, and few changes have been added to it in the last 100 years, although Lhermitte in 1925 and Baudouin in 1930 made important contributions to define the characteristics of thalamic hemorrhage.
On the other hand, Fisher emphasized language disorders and alterations in ocular motility produced by thalamic lesions.
Thus, on the other hand, twenty years after that first description, Foix, Massson and Hillemand, other researchers, showed that the most common cause of the syndrome was obstruction of the thalamogeniculated arteries (branches of the posterior cerebral artery).
The most distressing symptom of the thalamic syndrome is pain; it is a pain that is usually intractable, intense, disabling and constant. The thalamic pain is of central origin, that is, its origin is in the cerebral cortex.
The pain, in addition, is refractory and unpleasant, and resists analgesic medication. The pains are usually presented as an initial symptom in 26 to 36% of patients. The sensation of pain is burning and lacerating, and is commonly associated with painful hyperesthesia in the same distribution. This hyperesthesia is defined as an exaggerated sensation of tactile stimuli (such as a tingling sensation).
Other important symptoms in the thalamic syndrome are paresthesias, mild transient hemiparesis, hemicoreoathetosis, hemihypoestesia, hyperalgesia, allodynia and hemiataxia with astereognosia of variable intensity.
Specifically, patients with this syndrome manifest a sensory loss contralateral to the lesion in all modalities. In addition, there are also vasomotor disorders, severe dysesthesia of the involved body and sometimes choreoathetoid or ballistic movements.
The cause of the thalamic syndrome is an injury in the thalamus. Specifically, said injury involves the inferior and lateral nuclei.
The most common lesions of the thalamic syndrome are of vascular origin (cerebrovascular accidents), although there are also other types of lesions, such as those of metabolic, neoplastic, inflammatory and infectious origin.
On the other hand, referring to the vascular origin of the syndrome, thalamic infarcts are usually due to the occlusion of one of the four major vascular regions: posterolateral, dorsal, paramedian and anterior.
The treatment of thalamic syndrome mainly involves the associated pain. In the past, the treatment was based on neurosurgery, with interventions such as thalamotomies (removal of a small area in the thalamus), mesencephalotomies (removal of the mesencephalon) and cingulotomies.
However, new neuroquiurgic treatments have been established, such as spinal cord stimulation, motor cortex stimulation and chronic deep brain stimulation, using stereotactic approximation techniques.
On the other hand, other new treatments have also been used in recent years, from opioid medications, tricyclic antidepressants and analgesics-antiepileptic drugs (for example, gabapentin).