What is thalamic syndrome?
It is a syndrome that develops when the thalamus is affected, known as thalamic lesions, which can be contralateral and cause general neurological, neuropsychological and neuro-ophthalmological syndromes.
The thalamus occupies approximately 80% of the diencephalon. The diencephalonis a set of structures, located just below the brain, these are the thalamus, hypothalamus, subthalamus, ventricles and much more.
The thalamus is composed of different nuclei, organized into different groups. Each receives information from one part of the nervous system and sends it to another region of the nervous system. It acts, in a way, as an intermediary.
Among the most relevant brain functions of the thalamus are memory,emotions, the wake-sleep cycle, sensory and motor control, as well as the processing of sensory information, before being diverted to the cerebral cortex.
Its position, just below the cerebrum and above the brainstem, is highly relevant as it acts as the point that transmits information from one site to another.
Due to the multiple functions associated with the nuclei of the thalamus, a lesion at this level can produce a variety of symptoms, which are still not fully understood.
However, there is a syndrome that is widely known in neurology, called Dejerine-Roussy sensory syndrome or central thalamic pain syndrome, which we will explain later.
Causes of thalamic syndrome
The causes of thalamic syndrome are broadly similar to those of other types of stroke. Blood flow problems, hemorrhages, trauma, genetic and environmental factors play an important role.
Next, we will name some of the possible causes.
Interruption of blood flow
Thalamic syndromes are due in most cases to vascular thalamic lesions, where the interruption of blood flow by parenchymal hematomas constitutes 20-35% of all cerebral hemorrhages.
Trauma, brain tumors, hemorrhages and vascular malformations can cause an interruption of blood flow, although they are less frequent, they can also trigger thalamic syndromes.
A Cerebrovascular Accident (CVA) is characterized by a local or general disturbance of the cerebral circulation, which can have a variable duration, and multiple causes. They are classified into stroke of ischemic origin and stroke of hemorrhagic origin.
Ischemic infarcts can compromise the branches of the arteries that supply the thalamus, such as the posterior communicating artery, the basilar artery, or the posterior cerebral artery.
This results in a thalamic lesion due to stroke, with ischemic infarcts after parenchymal hematomas being the second most frequent cause of thalamic syndromes.
Arterial hypertension is an important risk factor in the rupture of intracranial blood vessels, which can serve as the basis for the development of a microaneurysm.
Therefore, any pathology or condition that predisposes to an obstruction or rupture of small vessels that may compromise the adequate irrigation of the thalamus, predisposes to a possible thalamic syndrome.
Over the years, cardiology research groups have sought to establish a relationship between certain health conditions and the risk of suffering a stroke. The different results showed that important risk factors do exist.
One of them has been very well studied, and they are arrhythmias. Atrial fibrillations and ventricular arrhythmias, which have been found to be associated with strokes, especially in patients with arterial hypertension.
Another important finding is that, in the electrocardiogram, findings have been observed that have also been associated with a stroke, such as ST segment depression (a very common finding in patients with heart disease).
Some explanations for this phenomenon are: arrhythmias disturb blood flow to the brain, causing low oxygen concentrations that can lead to a heart attack.
Another explanation is that, in the setting of atrial fibrillation, the rapid, repeated beats can form blood clots in the inner walls of the heart , which can break off and travel to a region of the body (such as the brain).
Hypercholesterolemia (literally, high blood cholesterol) is a risk factor for many cardiovascular diseases.
It is a common metabolic phenomenon in developing or developed countries, due to a greater consumption of processed food. Generally, it is not an isolated event, but is associated with other conditions (type 2 diabetes mellitus, high blood pressure, sedentary lifestyle, etc.).
All of these factors are atherogenic, that is, they encourage the formation of fatty acid plaques on the walls of the arteries, called Atheromastag. These have a number of consequences.
They are able to: decrease blood flow to an area, completely occlude blood flow to a region, and can detach from the arterial wall, travel through the bloodstream, and lodge in another region.
Therefore, it is not surprising that atherosclerosis is a very serious risk factor for diseases such as myocardial infarction, intestinal infarction, renal infarction and stroke.
A sedentary lifestyle, that is, the lack of physical exercise, goes hand in hand with hypertension, atherosclerosis and other diseases. However, it would be more correct to label a sedentary lifestyle as one of the origins of these.
An inadequate diet, mixed with a sedentary lifestyle full of stress, activate biological responses, raising pro-inflammatory cytokines, lowering our defenses, altering our mood.
The net result: a weak body, from a metabolic and nutritional point of view, with widespread inflammation, which insidiously leads to diseases of all kinds, where the heart, circulation and brain do not escape its effects.
Certain diseases are products of a specific phenotype (that is, the genetic pattern of each individual), which can culminate, in the worst case, in a stroke.
An example of them is Fabry disease, a rare genetic condition caused by the deficiency of an enzyme responsible for degrading a type of lipid in our body, known as sphingolipids.
By accumulating in a non-specific way in almost all tissues of the body, they generate all kinds of syndromes. At the level of the cerebral arteries, the deposit increases to such an extent that it compromises the blood supply.
One of the characteristic signs of the disease is the pulvinar sign. When performing a computed tomography of the patient’s brain, an affectation of the pulvinar nucleus of the thalamus is shown, which could contribute to the appearance of strokes.
Symptoms of thalamic syndrome
Different arteries supply blood to the thalamus, if any of these is unable to fulfill its function, a certain group of nuclei is affected, giving rise to different clinical syndromes. Next, we will name a few.
Severe limb pain
It is a clinical phenomenon that occurs more frequently in lesions in the right region of the thalamus. The pain is accompanied by a constellation of other symptoms, known as Dejerine-Roussy syndrome.
It is named after French neurologists, who described this syndrome for the first time, at the beginning of the last century. These were Joseph Jules Déjerine and Gustave Roussy.
In their report Le syndrome thalamique , they wrote that certain patients, after a stroke, experienced severe, persistent, paroxysmal pain (that is, it started spontaneously) on the side of the body suffering from muscle weakness.
This pain could be caused by an alteration in the sensitivity pathways, which lead to stimuli (touch, temperature, vibrations, etc.), from the nerves in our skin to our brain. The type of pain generated by a thalamic syndrome is called central pain.
Weakness and paralysis of affected limbs
The thalamus, as we mentioned, participates not only in sensitivity, but also in memory, emotions, and motor skills. Hemiparesis is common in patients with Dejerine-Roussy syndrome.
Motor deficits are usually accompanied by other sensory deficits and abnormal movements, produced by obstruction or hemorrhage of the inferolateral artery of the thalamus, which supplies the geniculate nucleus, the ventral posterior and lateral.
Muscle weakness occurs on the opposite side of the region from the affected thalamus. Therefore, an infarction of the left loop of the thalamus generates affections of the face, arm and right leg.
The tingling sensation generally accompanies the neuropathic pain described above. In a case report, an elderly patient developed a thalamic syndrome, after having suffered a subarachnoid hemorrhage.
The patient described that the pain and tingling started in his left foot and over five years, this pain escalated, reaching the entire left half of his body. Tingling is a manifestation resulting from altered sensitivity.
Ataxia, and its different variants, is defined as “the lack of coordination in the movement of the different parts of the body”.
Uncontrolled movements generally occur on only one side of the body, although they can occur on both if the vascular damage to the thalamic level occurred on both the left and right sides.
It can manifest in different ways: tremors in the hands, difficulty in successfully completing tasks or involuntary eye movements (involuntary drooping of the upper eyelid or weakness of the eye muscles).
Intensive perception of sensory stimuli
If the “relay station” of ourNervous System begins to fail, then the sensory or motor signals may not be transmitted or, if they are, they may be altered.
This is the case of dysesthesia, where the patient describes perceiving an unpleasant, even painful, tactile sensation, although it can also be described as inappropriate.
In other words, the patient’s ability to discern what is felt by touch is completely altered, experiencing pain or itching for no apparent reason.
Another perception disorder is hyperesthesia. Contrary to the previous one, where perception is altered, in this case, it is exaggerated. Mild and painless stimuli can cause intense and even painful sensations.
Increased sensitivity to pain
Hyperalgesia and allodynia fall into this category. How are the two different? The first may be an exaggerated response to pain. For example, a small prick can be perceived as intense pain.
The second, allodynia, is a perception of pain to a stimulation that normally is not. For example, gentle pressure against a part of your body can cause a dull ache, or brushing or gauging can cause a sharp pain.
As a clarification, both hyperalgesia and allodynia are two different types of hyperesthesia (altered stimulation). They indicate that the patient’s pain threshold has been lowered, as well as an increased response to pain.
Difficulty coordinating voluntary movements
The ability to accurately coordinate our movements, even the smallest, is the end result of a complex process. The thalamus is involved in it, as it relays information to and from the brain and spinal cord.
Any injury at these three levels makes it impossible for voluntary movement (taking a pencil, lifting a box, moving one foot forward, etc.) from taking place. A simple task becomes magnitudes of times more difficult.
Not only because motor capacity is reduced, but also because complex voluntary movement depends on a feedback system, where any action is processed and memorized, to evaluate the effectiveness of our movements.
For example, young children grasp objects roughly and use more force than they should. But, the repetition of these actions serves as feedback, where we become more skilled with our hands and feet.
When the thalamus fails, this system fails as well. We are unable to execute tasks with the required speed, force and magnitude, since our ability to control it is altered.
Difficulty distinguishing objects by touch
The basic sense of touch is not as basic as it seems, it is actually extremely complex. Our body is capable of detecting the shape, size and temperature of an object, as well as the vibrations and pressure that objects exert on our body.
In the different alterations of sensitivity, whether they are increased or reduced, the person’s ability to discern and describe objects with touch alone also stop working correctly.
ToBlunding effect occurs , where the person feels that something is touching their body, but is unable to recognize where it is touching it, what is touching it and with what pressure.
Thalamic syndrome treatment
The central pain produced by the thalamic syndrome is not easy to treat. For some patients, the pain is unbearable and does not subside easily.
Fortunately, pharmacological advances (medications) and surgery have allowed significant advances. Next, we will name a few.
Medicines recommended by specialists
Even a century ago, Dejerine and Roussy noted that the pain was constant and disabling, capable of withstanding the effects of painkillers.
Today, analgesics-antiepileptics, antidepressants (certain patients may develop)personality disorders or be affected by constant pain) and others, such as opioids, are used.
As the first line of treatment, amitriptyline is applied, a tricyclic antidepressant, which modifies the transmission of certain biochemical substances in the brain, called neurotransmitters .
Thus, the activation of the response to pain is decreased and the transmission of stimuli is improved.
Gabapentin, a potent antiepileptic and analgesic, has shown favorable effects. Its function is to increaseGABA levels , a substance that inhibits the transmission of information (in this case, it reduces pain).
Another benefit of drug treatment, if they are effective, they avoid the need to subject the patient to surgical treatment (as we will explain below).
It is a form of minimally invasive surgery. They are a set of techniques that use devices capable of generating three-dimensional coordinates, allowing the surgeon to be able to accurately locate small structures in our body.
These devices (or techniques) are, for example, magnetic resonance or computerized axial tomography, which provide a three-dimensional image of the patient’s brain, in real time.
A stereotactic appliance is fixed to the patient’s head, using screws and rods. It is a semicircular ring, adjustable to different coordinates (obtained previously) in such a way that, in the center of the ring, the area to be operated is located.
Local anesthesia is applied to the scalp and a small incision is made. A small electrode is introduced that allows the monitoring of the electrical activity of the area, allowing a greater degree of precision.
Once the area is located, ablation surgeries are performed, where the globus pallidus (pallidotomy) or the thalamus (thalamotomy) can be removed. Electrical stimulation of the thalamus can also be used to treat pain.
The effects of electrical stimulation or ablation of the thalamus on the pain syndrome are effective in 80% of patients, who experience complete long-term relief.