Sensory ataxia

In neurological impairment of deep sensitivity, sensory ataxia develops - inability to control movements proprioceptively, which is manifested by unsteadiness of gait, impaired motor coordination. Motor disorders sharply intensify if the patient closes his eyes. The pathology is not completely cured: patients undergo intensive rehabilitation measures aimed at supporting the musculoskeletal system and improving the quality of life. [1]

Epidemiology

Compared to cerebellar ataxia, sensory ataxia is relatively rare. In most cases, it occurs as a result of damage to the posterior columns and, as a consequence, a disorder of proprioceptive afferentation, which can be observed, in particular, in patients with Friedreich's disease, avitaminosis E and _B12, neurosyphilis.

Sensory ataxia is diagnosed by a clear proprioceptive insufficiency and a marked increase in clinical manifestations against the background of eye closure. Pseudohyperkinesis of the affected limb is often noticed.

The term is derived from the Greek word "ataxia", which translates as "disorder". Sensory ataxia can act as a syndromal addition to the diagnosis in traumas and degenerative pathologies of the central nervous system. As an independent nosologic unit, the problem is considered only in some pediatric hereditary diseases, so the real frequency of development of this disorder is unknown (secondary ataxia, as a sign accompanying another pathology, statistics usually does not take into account).

Hereditary sensory ataxia is a very rare (orphan) disease. This group includes diseases that occur in less than 1 case per 2,000 population.

Causes of the sensory ataxia

Sensory ataxia is due to impairment of deep types of sensitivity, in particular:

• musculo-articular sensitivity, which receives signals about the position of the torso in space;
• of vibration sensitivity;
• feelings of pressure and weight.

Movement and coordination disorders in sensory ataxia result from the failure to receive kinesthetic information from the central parts of the proprioceptive apparatus, i.e., the system does not receive signals, for example, about muscle contractions. The pathology is not considered as an independent nosological unit, but is a complex of symptoms, which is characterized as a syndrome of sensory ataxia, occurring in many neurological diseases. The clinical picture in this case depends on individual features of damage to proprioceptive nerve directions.

The disorder can be found in different parts of the proprioceptive apparatus - in particular in the posterior spinal columns, spinal cord ganglia, posterior roots, along the level of the medulla oblongata, cortex or thalamus. The problem is often due to vascular injury (cerebral or cerebrospinal stroke), myelitis, tumor processes in the brain or spinal cord, funicular myelosis, neurosyphilis spinal dryness, spinal cord injuries, multiple sclerosis.

In some patients, the occurrence of sensory ataxia is associated with surgical interventions on the spinal cord or brain.

Peripheral parts of the proprioceptive apparatus are affected in patients with Guillain-Barré syndrome, polyneuropathy of diabetic, toxic, infectious toxic or amyloid origin. In addition, sensory ataxia is found against the background of certain genetic pathologies - in particular, we are talking about Fredreich's ataxia. [2]

Risk factors

Sensory ataxia develops if the following structures are affected:

• The posterior spinal canals are the cuneiform and bundle of Goll (ascending spinal canals). This is the most common disorder in sensory ataxia. It can be observed as a consequence of trauma associated with sharp bending of the spinal column.
• Peripheral nerves. Affected against the background of disorders of axons of nerve fibers, myelinopathy, Wallerian transformation caused by trauma or ischemia of the peripheral nerve.
• Posterior roots of the spinal cord (due to trauma, compression, etc.).
• The medial loop, which is located in the brainstem and is part of the conductive canal that carries impulses from the musculotendinous apparatus and the bulbothalamic system.
• The thalamus, which ensures the realization of unconditioned reflexes.

In some patients, the appearance of sensory ataxia is associated with contralateral parietal lobe lesions.

Sensory ataxia most often develops against the background of such pathologies:

• Spinal dryness (a type of tertiary neurosyphilis).
• Funicular myelosis (degeneration of the lateral and posterior spinal cords as a result of prolonged _B12 avitaminosis or folate deficiency anemia).
• Polyneuropathies (diphtheria, demyelinating, arsenic neuropathies, Guillain-Barré, Refsum and Krabé syndromes, etc.).
• Vascular pathologies (in particular, ischemia of the spinal arterial trunk).
• Tumor brain processes.

Sensory ataxia is also found in the rare autosomal recessive Friedreich's disease. Coordination motor disorders occur against the background of damage to the myocardium and other systems and organs.

Pathogenesis

Sensory ataxia develops due to lesions of peripheral nerve fibers, spinal posterior roots and columns, medial loop. These fibers carry proprioceptive impulsation, carrying information to the cerebral cortex about the position of the body, limbs and their movements.

Musculoarticular sensations are determined by the receptor apparatus represented by Pacini's lamellar corpuscles - unencapsulated nerve endings that are present in joint capsules, ligaments, musculature, and periosteum. Signals from the endings follow first-order sensory neurons entering the spinal posterior horn and further into the posterior columns.

Proprioceptive flow is transported from the legs by means of the thin Goll bundle located medially, and from the arms by means of the wedge-shaped Bourdach bundle located laterally.

The nerve fibers involved in this transport form synapses with second-order sensory nerve cells.

Branches of the second-order nerve cells cross, then in a medial loop pass to the ventral posterior thalamic nucleus, where sensory nerve cells of the third order are localized, having a connection with the parietal lobe cortex.

The transport of nerve signals that provide sensation to the arms and legs is accomplished through the posterior spinal roots. The nerves in the posterior spinal cord are responsible for sensory sensation and pain.

When the posterior roots are damaged, the sensitivity of the cutaneous area, which is innervated by the corresponding nerve fibers, is lost. At the same time, tendon reflexes are reduced or lost, although motor activity is still present.

When part of the ascending pathway is damaged, the spinal cord loses the ability to transfer information about limb position to the brain, resulting in impaired motor coordination.

With polyneuropathy and damage to the posterior columns, gait and, in general, motor activity of the legs are symmetrically disturbed. Arm movements are not affected or are only slightly affected. [3]

Symptoms of the sensory ataxia

Manifestations of sensory ataxia are characterized by a violation of motor sensations coming from one's own body. At first, this can be noticed by a change in a person's gait: the patient begins to walk with legs spread wide, incorrectly bending and extending them at the knee and hip joints, and "landing" the foot after each step. Practicing neurologists call this gait "stamping" or "tabetic", and the patients themselves call it "slumping" or "absorbent cotton".

The patient tries to correct the proprioceptive deficiency with the help of constant visual control. For example, while walking, the person stares tirelessly at his feet with his head downward. If visual control is interrupted, the movement disorder worsens again. Walking blindfolded or in dark conditions becomes impossible.

Sensory ataxia involving the upper extremities is accompanied by a disorder of coordination and arbitrary motor skills, as a result of which ordinary activity suffers. In particular, it becomes difficult for the patient to eat first dishes with a spoon, drink water from a glass, fasten small parts of clothing, use a key. At rest, disorderly involuntary movements of the phalanges of the fingers of the type of hyperkinesis draw attention. A distinctive feature of sensory ataxia is that pseudohyperkinesis disappears with the onset of voluntary motor activity.

The first signs in sensory ataxia can be different, which depends on the features of the lesion of the proprioceptive mechanism. If the pathological process captures the posterior columns at the level of the thoracolumbar sections, ataxia is noted only in the legs. If the posterior columns above the cervical thickening are affected, the problem is manifested in both the upper and lower extremities. With unilateral pathological changes in the proprioceptive apparatus before the transition of fibers to the other side, homolateral hemiataxia develops, which is characterized by the occurrence of a violation in half of the body on the side of the lesion. In unilateral painful changes of the deep sensory channels after their crossing, the problem is manifested by heterolateral hemiataxia: the limbs opposite to the affected side are affected.

Stages

Depending on the clinical manifestations, such stages of sensory ataxia are distinguished:

1. Mild stage - observed in patients with limited damage to the wired spinal-cerebellar tract. Deep sensitivity is not impaired, motor coordination and gait are moderately affected.
2. The middle stage, or moderately severe, is characterized by a decrease in the tone of flexor and extensor muscles, which makes it much more difficult for the patient to perform ordinary household activities. General reflexes also decrease, the sense of support is lost, and there is a need for constant visual control during walking. The gait becomes typical of sensory ataxia.
3. Severe stage: the patient loses the ability to walk and stand.

Forms

Sensory ataxia happens:

• Static, which is manifested by impaired posture retention (which is particularly evident if the patient closes his eyes);
• dynamic, in which pathological signs are manifested with the onset of motor activity.
• In addition, if the pathways of deep sensitivity are affected, distinguish:
• unilateral ataxia, which develops when the thalamus or brainstem is affected on the opposite side;
• bilateral ataxia formed when the pathologic focus is located in the area of crossing of the medial loop.

Complications and consequences

Sensory ataxia is a pathological condition characterized by impaired motor coordination. With the progression of this disease, a person becomes disabled, the quality of life and its duration suffer.

Shivering in the limbs, frequent dizziness, loss of the ability to move independently and perform basic activities, disorders of the respiratory and digestive systems - such disorders significantly complicate the life of the patient. Over time, respiratory and chronic heart failure develops, immune defense deteriorates, there is a tendency to frequent infectious pathologies.

Nevertheless, it should be understood that these adverse effects do not occur in all patients with sensory ataxia. In individual patients, provided that all medical prescriptions are followed and timely drug therapy is carried out, the clinical picture of the disease does not worsen and the quality of life does not decrease. Many patients live to an advanced age.

A particularly unfavorable prognosis can be discussed if the patient is found to have malignant neoplasms, epilepsy, encephalitis, cerebral circulatory disorders.

Diagnostics of the sensory ataxia

Sensory ataxia is detected during the initial examination of the patient by a neurologist. Hypotonia of the muscles (flexors and extensors) of the affected arms or legs, loss of deep sensitivity are noted. When attempting to assume the Romberg pose, shakiness is noted, with significant strengthening when closing the eyes. The posture with holding the upper limbs stretched forward is accompanied by false hyperkinesis (pseudoathetosis).

Coordination tests are also disturbed: the patient cannot get his finger into the tip of his own nose, he cannot put the heel of one foot to the knee joint of the other foot. Outwardly, a typical tabetic gait is determined. When trying to run the heel of one foot over the crest of the tibia of the other foot, there are jerks and the heel is turned sideways. [4]

The main point is to find out the cause of the pathological condition, for which such laboratory and instrumental diagnostics are used:

• examination by a neurologist to rule out other types of ataxia (differential diagnosis);
• general blood and urine tests;
• examination of cerebrospinal fluid, taken during lumbar puncture, to exclude multiple sclerosis, inflammatory diseases of the central nervous system, neurosyphilis;
• computer and magnetic resonance imaging of the brain and spinal cord;
• electroneuromyography to assess the condition of peripheral muscles and nerves;
• genetic counseling to rule out hereditary pathologies (sometimes with DNA testing).

Differential diagnosis

Differential diagnosis is made with other types of ataxia.

Vestibular ataxia develops when any area of the vestibular mechanism is affected, in particular, the vestibular nerve, the nucleus in the brain stem, the cortical center in the temporal lobe of the brain. The vestibular nerve originates in the node of Scarpa, localized within the internal auditory canal. The peripheral cell-node branches lead to the three semicircular canals, and the central branches lead to the vestibular nuclei of the brainstem.

Typical manifestations of vestibular ataxia are: systemic vertigo, nausea (sometimes to vomiting), horizontal nystagmus. Pathology is detected more often against the background of stem meningoencephalitis, tumor processes of the posterior cranial fossa, fourth ventricle, Varolian bridge.

If the pathological process affects the frontal and temporo-occipital region, there are disorders of motor coordination in the type of cortical ataxia, which has similarities with cerebellar ataxia. Cerebellar and sensory ataxia have the following main differences:

• development of cortical ataxia is noted on the side opposite to the focus of cortical lesion (in cerebellar lesions, the side of the lesion is affected);
• In cortical ataxia, there are other signs indicating lesions of the frontal zone (mental and olfactory disorders, facial nerve paresis), occipitotemporal zone (scotoma, hallucinations of various types, homonymous hemianopsia, sensory aphasia, etc.).

Cortical ataxia is observed mainly in intacerebral pathology with frontal or occipitotemporal localization. These are encephalitis, circulatory disorders of the brain, tumor processes.

As for sensory ataxia, it develops against the background of damage to the posterior columns, less often - posterior roots, peripheral centers, parietal lobe cortex of the brain, optic tubercle. Most often the problem occurs in patients with spinal dryness, polyneuritis, funicular myelosis, vascular or tumor disorders with localization in the zone of the optic tubercle, parietal lobe of the brain, internal capsule.

Treatment of the sensory ataxia

Sensory ataxia is difficult to cure, so the main treatment is aimed at correcting the general condition of the patient, inhibiting the progression of the disease, improving the quality of life.

A comprehensive approach is used, including drug therapy, physiotherapy and physical therapy (PT). Supportive therapy is carried out with the use of such medications:

• B-group vitamins - affect the state of muscle tissues, contribute to the elimination of spasms (administered as intramuscular injections);
• riboflavin and immunoglobulins - used for the purpose of stimulating nerve fibers;
• nootropics - normalize brain activity, improve the transmission of nerve impulses, can be used for a mild tranquilizing effect, correction of psycho-emotional state;
• Multivitamin preparations - used to improve immunity.

The doctor may prescribe anticholinesterase drugs if there is neuritis or severe muscular dystrophy. Complex treatment contributes to the activation of muscle activity, optimizing the work of nerve receptors responsible for motor coordination. Nevertheless, it is impossible to completely get rid of sensory ataxia, which is due to the impossibility of eliminating the underlying causes of the development of the disorder.

Physiotherapy and physical therapy should be used by the patient on a regular basis. Physiotherapeutic procedures are prescribed in courses, and physical therapy exercises are first performed under the guidance of a therapist, then on their own or under the supervision of close people. Additional use of special simulators, such as those that help to develop flexion and fine motor skills of the hands, is possible.

Long walks (up to 1 km, every day), exercises with a small ball are considered useful. Excessive exercise is not welcome: it is enough to do gymnastic exercises for about half an hour a day. [5]

Prevention

There are no specific methods of prevention of sensory ataxia. Specialists insist on timely medical attention, which contributes to the early detection and treatment of diseases that can later cause the development of ataxia.

Other preventive measures include:

• timely treatment of infectious and inflammatory processes in the body;
• monitoring blood pressure readings;
• Exclusion of those activities and sports that can lead to head injuries;
• leading a healthy lifestyle, avoiding bad habits, observing a work and sleep schedule, and eating a balanced diet with quality products.

Forecast

Sensory ataxia can be cured only if the cause of the pathological condition is completely eliminated, which is quite rare. The most unfavorable prognosis is noted in patients with hereditary and malignant forms of the disease, as well as in the development of stable foci of degeneration: in such situations, patients are prescribed only supportive therapy to improve the quality of life and slow down the progression of the disorder.

If the root cause of the pathology can be eliminated and the affected area of the proprioceptive tract can be restored, then we can talk about a possible favorable outcome. In most patients, sensory ataxia is characterized by steady progression, the condition of patients gradually deteriorates, which is especially noticeable in the absence of appropriate supportive therapy and rehabilitation.