Juan Pablo Recagno Cepeda
Normally the harmony and regularity of voluntary movements depend on a precise coordination between all the numerous muscles involved in any movement; likewise, walking and standing require a correct distribution of the nervous stimuli, well correlated in a suitable time.
When the mechanisms that regulate this coordination fail, there is an incoordination of the movements that is called ataxia and that may be due to an alteration: 1) of the reception of the stimuli that capture the sensitivity of the same muscle or deep sensitivity: sensory ataxia; 2) of the organs destined fundamentally to maintain balance and posture, the labyrinth: labyrinthine ataxia; and 3) the cerebellum, the central organ of tone regulation: cerebellar ataxia.
Some other forms of ataxia are described, although without major clinical significance and of doubtful interpretation; but it is interesting to emphasize that sight, whose annulment does not produce ataxia, is an important correction and substitute factor for some coordination-related inferences.
- Sensory ataxia. Also called peripheral, it always occurs coinciding with a serious alteration of deep sensitivity and its consequent motor problems, hypotonia and areflexia. The most typical case is that of the tabes, which today is seen exceptionally and which produces a diffuse commitment, of luteic origin, of the posterior roots and the posterior cords of the spinal cord; Muscle sensitivity is lost and the subject is unable to perceive the exact location of her limbs; and from there derives the importance of sight to supply her disability, for which she needs to permanently look at her own movements to try to correct them. As in all ataxia, there is no paralysis, but the movements have lost their harmony and decompose with the lost rhythm and become irregular; they are oscillating and do not reach the desired object, they usually exceed it; Furthermore, upon arrival it is impossible for them to keep the limb fixed, because they cannot keep a fixed position. It is interesting to note that, while in the cerebellum the intensity of its disorder is aggravated with the progression of movement, which can lead to intentional tremor, sensory ataxic has it since the initiation of movement. The foot station is oscillating; the individual cannot easily hold onto one foot and when closing his eyes —or even when looking up— he falls because he loses stability: he has a positive Romberg sign. The march is insecure, with the limbs separated, raising the feet exaggeratedly and letting them fall with a crash, hitting the ground; it is a tapping march that the individual also does looking at the ground and his feet,
- Labyrinthine ataxia. The labyrinth is one of the basic systems for maintaining posture and balance; when one of the labyrinths fails, the subject presents an ataxia, which has the particularity of being referred to the head and which is agitated by its movements; the subject is dizzy or dizzy —we will see the exact meaning of both terms— and has difficulties standing up, as he staggers, with his legs apart and a feeling of always pushing towards the same side, towards which he tends to fall. It presents a positive Romberg sign, although somewhat delayed compared to sensory ataxic, and gait deviation, always towards the same side. The coexistence of auditory symptoms and signs is common.
- Ataxia cerebelosa.The cerebellum is a fundamentally motor organ, whose function is to regulate movements, ensuring the continuity and measurement of motor impulses (Thomas). The maximum exponent of its alteration —especially if its nuclei are affected— is the incoordination of the voluntary movements, globally called ataxia cerche slab, and in particular known with various names of practically similar meaning: dysmetry, dyssynergia, adiadochokinesia, etc. The rhythm, the extension, the speed, the measure and the force of the movements are fundamentally altered, whether they are simple or very complex: there are irregularities in the acceleration and deceleration of their phases, revealed with the classic finger-nose and heel tests. -knee, where the toe or heel oscillates around the desired point, sometimes appearing when approaching it, oscillations with some rhythmicity, which constitute the intentional tremor of the cerebellum. Likewise, if you want to make opposite movements in rapid succession, you notice a clear difficulty and also decomposition of the movement that is divided into a series of smaller ones; of the same mechanism are the explosive word and the disadvantages of ocular motility, which translate into an irregular oscillation of the eyes that can be called non-toxic nystagmus. All this is due to instability in the normal fixation of the joints involved due to failures attributable to modifications of the gamma loop under cerebellar control. In the standing station there is an increase in the support base, with oscillations of the trunk and with the arms abducted to maintain balance; Romberg's sign is negative. The gait - sometimes impossible - is oscillating, progresses with hesitation and with a tendency to deviate from the straight line; when walking the limbs rise and lean abruptly and inconsistently; It is quite similar to the drunk march, but in this there is no increase in the base of support, it is very irregular and there is no tendency to correct large deviations in any direction. In unilateral lesions, ataxia is homolateral.
- Other forms of ataxia. When the pathways or centers related to coordination are affected, ataxia may appear; This way it can be found in brain stem injuries, but there, always accompanied by other signs that locate the injury. In parietal brain lesions, the region where the sensory pathways converge, there are signs that reveal their location and among them there may be ataxia. In the Déjérine-Roussy thalamic syndrome, hemiataxia is a fundamental component of the picture. The frontal ataxia, which simulates a contralateral cerebellar picture, is due to the premotor involvement that would involve the cerebellar projection pathways. The astasia-abasia seems to be simply an apraxia of the gait.
They constitute the fundamental manifestation of the nervous system. Any act can be qualified as such, if it has been provoked, if it occurs —or at least continues— without the aid of the will and without the control of conscience, and if it is possible to demonstrate that the impulses that originated it have traveled a circuit composed of at least two neurons, one afferent and one efferent, articulated by a synapse in a reflex center (Morin). Reflexes therefore basically have an afferent or sensory pathway that can be muscular or cutaneous, a reflex center and a motor efferent pathway.
There may be reflexes whose neurons correspond to the cerebrospinal nervous system, or components of the autonomic nervous system may be involved. We, in this section, will refer to the former, since of the others, only the pupillary reflexes have clear significance in the routine neurological examination.
The reflexes studied in the clinic are deep muscle and superficial muscle cutaneomucosa, usually called osteotendinosus and cutaneous, respectively. They consist of a brief, abrupt and immediate motor response, and by definition involuntary, to a peripheral stimulus; regardless of strictly physiological aspects, we can say that the reflex response is usually always the same, and that predictability is what gives it its high clinical significance. Likewise, the place where the synapse that closes the arch is established, the reflex center, always has a precise topographic location, from which its importance as locator value of a certain injury is deduced. The reflex center, in turn, is subject to permanent activity,
Deep or osteotendinous muscle reflexes are based on Sherrington's proprioceptive stretch or stretch reflex, already studied with muscle tone, where we stress the importance and mechanism of the gamma loop; These clinical reflexes have similar mechanisms and are produced by an abrupt stretching of the muscle due to percussion of the tendon, which excites and elongates the same neuromuscular spindles and causes an afferent stimulation that, due to its intensity, brings about a massive and synchronous discharge of the motor neurons. alphaclonic, which determine the muscular contraction of the reflex itself; this reflex is monosynaptic and the movement is brief and quickly ceases; at the same time there is an inhibition of antagonists that seems to be due to an inhibitory branch of the afferent pathway,
The muculocutaneus reflexes or superficial or cutaneous reflexes correspond to the flexion exteroceptive reflexes of neurophysiology and are defense or withdrawal reactions to generally nociceptive stimuli. Clinically, abdominal cutaneous, cremasterianos, and plantar are investigated; Babinski's sign appears to be part of a general lower limb withdrawal reflex. These are reflexes with evident purpose and their response is prolonged in time after stimulation, and they are polysynaptic; the old explanation of a vertical arch reaching the crust, superimposed on the classical arch and whose annulment would suppress the reflection, does not correspond to reality; her modifications in certain tables are not well explainable.
The details of the neurological technique and the maneuvers aimed at facilitating its obtaining, which demonstrate the importance of muscle relaxation so that they occur —in cases of great hypertonia they cannot be achieved— will be explained in another section; but it is interesting to remember from now that any asymmetry of the reflexes is abnormal, and that the evaluation of its intensity is a piece of information of relative significance that will need to be evaluated in the case of each patient.
Reflex modifications can be classified as: 1) increased or hyperreflexia; 2) decreased or abolished: hiccups or areflexia, respectively; 3) presence of pathological reflexes (or not normally obtainable), and 4) inversion of the reflexes.
Hyperreflexia can vary in its intensity and its exact evaluation can be very subjective; vivid reflections can mean nothing more than a personal characteristic or an exaggerated emotion; but if asymmetry of the reflexes is added between both sides, their diffusion, an increase in the stimulation zone and polykinetism, the suspicion of pathological hyperreflexia will be evident, which will be confirmed if there is an increase in tone and the presence of pathological signs (Babinski positive ). A pathological hyperreflexia almost always establishes the diagnosis of corticospinal tract compromise, usually of an organic nature, although it can be seen in some post-convulsion states, meningeal irritation, etc.
Hyporeflexia is also difficult to assess, as there are subjects with very weak reflexes and because fatigue also reduces them. On the other hand, an areflexia, confirmed after exhausting all the recommended techniques, is a fact of greater clinical value; However, in both cases, you will be faced with an alteration of the reflex arc, either in its afferent branch (polyneuritis, tabes, etc.), in the center (polio with fasciculations) or in its efferent branch (again polyneuritis in its motor component); The cancellation of the effector — myopathies — with exaggerated muscular atrophy will also lead to a clear hyporeflexia or a total areflexia. It is interesting to emphasize here that for reasons not clearly explained, as we said, abdominal skin reflexes usually disappear in lesions of the pyramidal pathway,
The pathological reflexes are mainly of the flexor type; thus, the Babinski sign and its substitutes, which are presented in. Pyramidal lesions seem to be the first link of the defense or withdrawal reflex of the lower limb, which in certain cases of severe bilateral injury to the medulla will condition the appearance of reflexes of spinal automatism caused by cutaneous excitation of the lower body. . Postural reflexes, of little clinical significance, are found in some extrapyramidal lesions. In cases of diffuse brain injuries that involve various motor components, pathological reflexes can be found, such as grasping, which would indicate a frontal location, snout, bulbar compromise index, etc.
The inversion of the reflexes has a variable practical importance, apart from the Babinski that we have already discussed and that would be an inversion of the plantar flexor reflex. The other cases would be due to an injury to the reflex center, which would annul the true reflex and allow, due to greater stimulation and central diffusion, the triggering of reflexes other than undamaged arc (as seen in abolitions of the Aquilian, when the percussion of the tendon excites dorsal flexor centers of the foot); or by mistakenly stimulating neighboring reflex zones causing different reflexes (such as percussion of the olecranon, instead of the triceps tendon, which produces the normal olecranon flexion reflex, instead of the extensor triceps.
The locator value of the reflex centers allows to precisely locate the site of an injury. Thus, in a traumatic medullary section at the upper dorsal level, the region directly affected will have the destroyed reflex centers and perhaps the roots; At this level, a limited areflexia will be found in said area; Above, the reflexes will be normal, since nothing has happened, and below, due to the compromise of the pyramidal beam, there will be, as in all her injuries, tendon hyperreflexia, abolition of the abdominal skin, reflexes of automatism and positive Babinski. This typical picture of chronic spinal section occurs after a phase of spinal shock, already mentioned in Chapter 45.
In tabes, where there is a diffuse lesion of the posterior roots and posterior chords, a total areflexia with complete atony will be observed.
In motor neuron injuries, we have already seen that there will be hyporeflexia with fasciculations that mark direct neuronal aggression.
In polyneuritic lesions, usually mixed, sensory and motor, both pathways of the arch are affected and consequently there will be hypo or areflexia.
In more limited lesions, for example, of a single root —and the herniated disc is characteristic in this regard—, a single reflex may be missing on one side, as in the hernia of the 5th space, where the affected root is exclusively SI, through which almost all the afference of the aquilian reflex passes and whose absence, as the only motor sign in a sciatica, is the locator of a hernia injury at that level
Synkinesias or associated movements are involuntary movements that occur on a paralyzed and hypertonic side, when passive voluntary movements are performed on the healthy side. They are very numerous, somewhat resemble reflexes and occur in pyramidal hemiplegics, which is why they are thought to be due to the release of inhibitory factors on certain centers. They are of very relative clinical importance.
From the detailed study of the motility disorders that we have listed, we can conclude that there are basically four motor syndromes, which it is essential to bear in mind before any modification of the motor components of the neurological examination:
- The pyramidal syndrome, due to injury to the first neuron or corticospinal contingent, which results in paralysis or paresis of systematized distribution —hemiplegias or paraplegia, fundamentally—, with added signs that allow an exact location of the injury and with increased tonism in the form of spasticity, without atrophy and with hyperrefiexia and the presence of pathological reflexes, of which the Babinski is the most significant; in addition there is absence of cutaneous reflexes and there are no abnormal movements, with the minor exception of some synkinesias in certain cases.
- Peripheral motor syndrome, due to injury to the second neuron, and which consists of usually segmental paralysis, with marked and rapid atrophy, hypo or areflexia, and clear muscle flaccidity. The place where the injury is located, in the long path of its path, will be diagnosed by the presence of fasciculations, when it is located in the motor neuron; by the absence of a sensitive component, in the various cases of pure involvement of the anterior root; by the concomitance of sensory disorders after the union of both roots; and by knowledge of the exact distribution of plexual trunks and peripheral nerves in the most distal lesions.
- Extrapyramidal syndromes comprise several entities that will be studied separately, but which in general are not accompanied by alterations in voluntary motility, but rather by abnormal movements of different types, spontaneous and permanent in wakefulness, increased muscle tone in hypertonia (chorea, which is hypotonic, is an exception) and bradykinesia.
- The cerebellar syndrome, which due to its clinical characteristics and its wide connections with the rest of the nervous system will also deserve a particular comment, and whose fundamental disorder is the incoordination of movements, for which reason abnormal movements are usually added —intentional tremor— , and hypotonia that conditions the appearance of pendular reflexes.