Carlos Ballario and Dra Laura Davidow

Coordination Disorders or Ataxias

Coordination of movements is a function of the cerebellum. It receives afferent information from the proprioceptive, vestibular, and visual pathways and from the cerebral motor cortex. With the information received from these inferences, he makes comparisons and makes the necessary adjustments to the movement.

Coordination disturbances or ataxias are caused by conditions involving the vestibular pathways, the proprioceptive sensory pathways, cerebellum, and / or their connections.

Ataxia cerebelosa

Cerebellar ataxia is characterized by the lack of coordination of voluntary movements, with their decomposition and lack of precision. These changes are called adiadochokinesis and dysmetry respectively. There are also disorders in the interruption of movement, with excessive rebound.

The gait is unstable with frequent falls, with irregular steps, resembling the drunken gait. Also, they cannot walk in tandem (one foot in front of the other with the heel hitting the back of the foot).

The foot station is supported by a wide lift base and may be accompanied by trunk tremors or hesitation and falls.

Other characteristics that accompany cerebellar ataxia are characteristic of lesions of this organ. The most prominent include: muscular hypotonia with pendulous reflexes, dysarthria, tremor of intention and eye disorders. Among the latter, the most frequent are: gaze-evoked nystagmus, rebound nystagmus, ocular dysmetry and optokinetic nystagmus.

Sensory ataxia

Sensory ataxia is caused by injuries involving the proprioceptive pathways. Therefore they can be located in the peripheral nerves, in the posterior roots of the medulla, in the posterior columns or in the medial lemniscus. Thalamic or parietal lesions are more rare as a cause of this syndrome.

Clinically, it manifests with gait ataxia that worsens when visual stimulation is suppressed. The steps are performed by widely raising the foot off the ground and then stomping with the heels due to the lack of proprioception (heel walking). Can improve with a cane.

The person can stand with their feet together while their eyes are open, that is, as long as they compensate with the visual stimulation. Closing the eyes exacerbates the imbalance or falls. This is called a positive Romberg sign.

Sensory ataxia can present impaired coordination of limb movements, with distinctive features of cerebellar alteration. In the proprioceptive alteration, the movements are abrupt, with loss of direction and with a very noticeable aggravation when the eyes are closed.

The presence of altered positional and vibrational sensitivity is characteristic and the reflexes may be altered.

Vestibular ataxia

Vestibular ataxia is primarily a gait ataxia and is usually associated with vertigo. Romberg's sign is positive. When marching the person leans to one side (the propulsion) and if asked to move in one direction and return with her eyes closed, she deviates in a certain orientation. This sign is named Babinski-Weil's star march.

In this type of ataxia the coordination of limb movements is not affected.

Other signs of vestibular dysfunction that are usually present are deviation of the indices and rotational nystagmus. There may also be hearing disorders.

Table 1- Differential diagnosis of ataxias

Physical examination of coordination

Walking and walking station evaluation

Romberg test (static coordination evaluation): the patient is asked to stand with the heels together with eyes open and then closed for 30 seconds. Normally the person will not move. The test is considered positive when you can stay in this posture with your eyes open and fall with your eyes closed. This indicates an injury to the proprioceptive or vestibular sensory system. In case of cerebellar injury the person will not be able to maintain this position with both the eyes open and closed.

Gait assessment: Gait is assessed by asking the patient to get up from a chair to walk in a straight line and return to the starting site. Then you will be asked the same with eyes closed. You will also be asked to walk in tandem, on the balls of your feet, and on your heels.

Dynamic coordination evaluation

Finger-nose test: the patient is asked to sit or lie down, after stretching the arm, touch the tip of the nose with the tip of the index finger. It should be done with both extremities, with eyes open and then closed.

This maneuver can also be performed with the explorer's index finger. The patient is asked to touch their index finger, first the scanner finger and then their nose, and repeat it several times.

Heel-knee test: the lying patient must touch the opposite knee with his heel, then slide the leg down on the tibial crest. The maneuver is repeated with both limbs and with eyes open and then closed.

Alternating rapid movements or Diadochokinesia:the patient must simultaneously rotate the hands in prone supination simultaneously. The patient may also be asked to touch the tip of each finger with the thumb quickly, back to front.

Rebound Maneuver: The patient flexes his arm hard against the examiner's resistance, then the examiner abruptly removes the resistance. If the arm is moved roughly towards the face, it means that the maneuver is altered and that the patient cannot maintain the balance between the agonist and antagonist muscles. This is seen in cerebellar lesions.

Study methodology:

Neuroimaging: In the presence of a cerebellar ataxia, a computed tomography or an MRI should be performed to evaluate the type of lesion and act early on accordingly. Injuries to the posterior fossa of the brain (hemorrhages, tumors, heart attacks, hydrocephalus, abscesses) are at risk of increasing intracranial pressure, herniation of the cerebellar tonsils with compression of the brain stem, and death.

Tomography is a useful study in emergencies. However, for lesions of the cerebellum or brain stem, the MRI is superior because it does not have the artifact that produces the bone in the tomography. Furthermore, it is also superior in demonstrating white matter lesions.

Neurophysiology: Nerve conduction studies can be performed for lesions of the peripheral nervous system and visual, auditory, and somatosensory evoked potentials to evaluate the different pathways.

Laboratory studies: general biochemistry is performed and to detect metabolic alterations, due to vitamin deficiencies, among others.

Cerebrospinal fluid: studied when infectious or inflammatory disorders are suspected.

Other determinations that may be required are muscle biopsies and genetic studies.

Reflex disturbances

Reflexes are involuntary muscle contractions triggered by sensory stimuli. They can be differentiated into a) deep reflexes or muscle stretching, also known as myotatics or tendons; b) superficial reflexes and c) pathological reflexes.

Deep reflexes

Deep or muscle stretch reflexes are the muscle's reaction to the passive stretch produced by percussion of the tendon. It is a reaction that depends on the integrity of the afferent and efferent pathways of the peripheral nerves and on the central inhibitory controls. The stimulus is mediated through the neuromuscular spindles and the tendon organs. These detect muscle strain, transmit the information to the marrow, and from there return the impulse that causes muscle contraction.

Exploring deep reflexes

Reflex examination is performed using a percussion hammer with a soft rubber end. The patient should be relaxed and the muscle in a medium degree of stretching. It is important to assess symmetry and the examiner must feel, in addition to visualizing muscle contraction. The response is classified as: 0 absent; + present but decreased; ++ normal; +++ increased not necessarily pathological and ++++ markedly hyperactive, pathological, often associated with clonus.

When the reflex cannot be obtained, reinforcement maneuvers can be performed. The most used is that of Jendrassik. This consists of asking the patient to perform an intense opponent traction of both hands, while examining the reflexes of the lower limbs. For upper limbs, the patient is asked to clench the teeth or to forcefully close the fist of the opposite arm to the one evaluated.

The exploration of the main deep reflexes is described below:

Bicipital reflex (C5-C6, musculocutaneous nerve): the patient is asked to place the semi-flexed and supinated forearm. In this position, the scanner holds the patient's elbow with the hand and places the thumb on the biceps tendon. Then he hits his thumb and the forearm flexes normally on the arm.

Triceps reflex (C7-C8, radial nerve): the patient rests his arm on the semi-flexed thigh, the explorer touches the triceps tendon. This causes the extension of the forearm.

Styrofoam reflex  (C5-C6 radial nerve): with the forearm semi-flexed and in the middle position between supination and pronation, the distal part of the radius is struck. The normal response is flexion of the forearm over the arm and supination.

Patellar reflex (L3-L4, femoral nerve): the patient preferably seated, with the knee flexed 90 degrees, the patellar tendon is struck and this causes the leg to extend over the thigh.

Achilles reflex  (L5-S2, tibial nerve): the patient lying down, with one limb crossed over the contralateral limb and the knee flexed, the Achilles tendon is struck and the plantar flexion is visualized. Dorsal flexion of the foot by the examiner may facilitate the maneuver.

Alterations

Decrease in deep reflexes: the decrease or absence of muscle stretch reflexes is caused by interference or injury to the reflex arc and its members. Therefore, the affectation can be of the receptors, the sensitive afferent pathway, the interneuron, the motor neuron, the efferent pathway or the effector apparatus.

Other processes that can produce hyporeflexia are: hypothyroidism, deep coma, general anesthesia and spinal shock.

Hyperactivity of deep reflexes:they are accompanied by increased muscle tone and clonus (repeated muscle contractions and relaxations) This alteration is due to injury to the pyramidal or corticospinal system, with the consequent elimination of the inhibition that the higher centers exert on deep reflexes.

Reflexes in hyperthyroidism, anxiety, tetany, and tetanus may also be increased.

Superficial reflections

Superficial reflexes are the reaction to a stimulus applied to the skin or mucosa. They are slower in latency than deep reflexes and tire with repeated stimuli.

Exploration of the main surface reflexes

1. Corneal reflex (cranial nerves V and VII): Gently rub the cornea with a cotton ball. The expected response is occlusion of the eyelid.
2. Pharyngeal reflex (cranial nerves IX and X): the pharynx is touched with a lower tongue and the pharyngeal muscles contract.
3. Cutaneous-abdominal reflexes: the patient lying down, the abdomen is stimulated laterally with a blunt object in the direction of the navel and on three levels. The normal response is the contraction of the abdominal muscles that produces the deviation of the navel towards the stimulus site.
4. Anal reflex (S3-S5, anterior hemorrhoidal nerve): using a cotton pad, the anal margins are stimulated and a contraction of the sphincter is expected.
5. Plantar reflex (S1-S2, tibial nerve): with a blunt object such as a key or pen, the outer part of the sole of the foot is rubbed from back to front. Under normal circumstances flexion of all toes occurs. When it is altered it is called Babinski's Sign (see below).

Alterations

The decrease or absence of surface reflexes is also caused by injury to the members of the reflex arc. However, the absence of abdominal cutaneous reflexes in the presence of deep reflex hyperreflexia has significant clinical significance. This is called reflex dissociation and is an expression of corticospinal pathway compromise. Superficial reflexes have a superimposed cortical pathway. Therefore, an injury to the corticospinal tract will cause the absence of these reflexes.

Superficial reflexes can also be abolished during deep sleep, coma and anesthesia. In some people they may be absent and have no pathological significance.

Table 2 - Correlation between the injury site and the alterations of the superficial and deep reflexes

Pathological reflexes

Pathological reflexes are not present in healthy subjects. They indicate injury to the nervous system. They usually appear with injuries of the primary motor cortex, the premotor cortex, the supplemental motor area, or the corticospinal descending pathways.

The most important are:

1. Oral responses: Applying a stimulus around the mouth produces sucking, sucking or lip protrusion responses. They are seen in diffuse cortical lesions or dementias.
2. Grip reflex: when gently stretching the fingers of the patient's hand, the patient responds by hooking the examiner's fingers. They are present in extensive lesions of the frontal lobes and brain degenerative processes.
3. Hoffman's reflex: The scanner holds the middle phalanx of the patient's middle finger and simultaneously flexes and rapidly releases the distal phalanx. The answer is flexing of the fingers, including the thumb. It suggests lesion of the corticospinal tract above C5-C6, although it may be present without being pathological.
4. Palmomental reflex of Marinesco and Radovici: the explorer stimulates the tenar region of the hand and the chin muscles contract. It is a sign of diffuse cortical compromise.
5. Clonus: are rhythmic muscle contractions produced by passive stretching of muscles or tendons. It occurs in states of muscular hypertonia associated with injury to the corticospinal tract. It is most often seen on the ankle and knee.
6. Extensor plantar reflex or Babinski's sign: after stimulating the sole of the foot with a blunt object, dorsiflexion of the big toe occurs, accompanied by a fan-shaped separation of the other toes.

There are other techniques to find this answer. The most used are: a) the Chaddock sign, where the external aspect of the foot is stimulated from the ankle forward to the fifth toe; b) the Oppenheim sign: pressure is applied with the thumb and index finger on the anterior surface of the tibia downwards, towards the ankle and c) the sign of Gordon: deep pressure is applied to the calf muscles.

Babinski's sign is one of the cardinal signs in neurology and its presence in adults always implies disease. It is a sensitive, specific clinical test capable of defining the lesion. It occurs in lesions of the corticospinal tract at any level from the motor cortex and its descending pathways. It can also occur in anesthesia, hypoglycemic shock, drug or alcohol poisoning, and in post-convulsive states.