Notes by dr Claudio Italiano
The cerebellum is an important station for integrating the motor activity of the
cortex, the basal ganglia, the vestibular apparatus and the spinal cord. It is
stimulated by the body surface (spinocerebellar and bulb-cerebellar beams, by
the specific organs of equilibrium (vestibulo-cerebellar pathway) and by the
cerebral cortex; the cerebellum acts on extrapyramidal motor activity and
intervenes on muscular activity, regulating its tone, static and stenosis
function. The main role of the cerebellum is fundamental in the coordination of
movements. In the cerebellum we can distinguish two voluminous lateral masses or
cerebellar lobes and a median or worm part. It is connected to the brainstem by
means of three pairs of peduncles:
- superior, which connects it to the midbrain and through which the anterior
sporo-cerebellar and cerebellar-rubro-thalamic bundles pass;
- medium, which connects it to the bridge and through which the
fronto-ponto-cerebellar and temporo-ponto-cerebellar pathways pass;
- inferior, which connects it to the bulb and through which pass the cerebellar
spino-cerebellar bundles, olive-cerebellar, cerebellar bulb and
vestibulo-cerebellar.
In order to correctly maintain the standing station or other position taken actively or passively or to correctly perform any movement, a precise distribution of contraction and decontraction of the different muscle groups is necessary, ie a well-coordinated function of the different muscles. To this end it is necessary that the higher centers are constantly informed, through the proprioceptive sensory pathways, both of the position and degree of contraction of the individual muscles and of the position of the various articular segments involved in the movement, so as to adapt the individual moment by moment. movements for the purpose to be achieved. A lesion of such routes or of the centers to which such information is received will be responsible for incoordination or ataxia. A static and dynamic ataxia is distinguished, depending on whether incoordination occurs in the maintenance of a given position or in the course of movement. The pathways of the propnoceptive sensibility reach the threshold of consciousness (if they pass through the beams of Goll and Burdach) or remain at the unconscious level (if they travel through the spino-cerebellar bundles); in the first case the sensory deficit can be partly compensated by the sight, whereas in the latter, this substitution is not feasible. Therefore, the first form of ataxia is called tabetic ataxia (as it is typical of the dorsal tabe): it is spinal or better sensitive due to a lack of proprioceptive information of the osteo-tendon receptors, originating from lesion of the afferent pathways of deep sensitivity, as they are associated always objective disturbances of sensitivity; characteristic and pathognomonic is the sign of Romberg. The second form should be referred to as cerebellar ataxia, due to a lack of muscle coordination by the cerebellum; no objective disturbances of sensitivity are observed in it. It is characterized by the absence of accentuation of the trunk oscillations in a position of attention (the Romberg is missing). The vestibular ataxia is different from the cerebellar ataxia because: the sign of Romberg is absent in the cerebellar ataxia, but it is a "labyrinthine rog", with lateral oscillations of the trunk towards a single side (corresponding to the injured labyrinth); varying the position of the head changes the direction of the march and there are hearing disorders (hypacusia) and the vestibular apparatus (nystagmus, vertigo).
Ataxia can sometimes be readily detectable, other times it is necessary to use
particular evidence to highlight it. Inviting the patient to perform a series of
actions (to get up, to walk, to stop immediately, to resume the march, to
back-seat, to sit down and to go up and down the stairs) in the event of ataxia
the motor incoordination is it manifests itself to every change of state or
motion, with uncertainty, slowness or exaggeration of movements, unsuitable
movements, not timeliness in the execution of order, oscillations of the body
and difficulty in maintaining equilibrium. The tests must be performed both with
open eyes and with eyes closed; in fact, in the case of sensitive ataxia, the
closing of the eyes will aggravate the disturbance. To highlight the ataxia in
the various segments of the body, the tests described with regard to cerebellar
ordering are used: the disturbances in cerebellar ataxia also occur with open
eyes and are more evident in rapid movements; in sensitive ataxia they are
accentuated with closed eyes and are manifested in both rapid and slow movements.
Characteristic of the cerebellar pathology is the appearance of disturbances of
the standing and walking, of muscular tone disorders, of elemental disorders of
the movement; the latter constitute cerebellar incoordination.
Expression of such incoordination are the following signs:
1) dismetria, ie lack of measure in the execution of a voluntary movement; it
manifests itself generally with exaggeration of its amplitude or hypermetry. The
latter is highlighted with the:
- index-index test: the patient is asked to touch the index of the right hand
with that of the left hand, first with eyes open and then with eyes closed;
- index-nose test: the patient, invited to touch the tip of the nose with the
tip of his index, makes a larger movement exceeding the goal; if during the
approach to the nose the hand stops halfway to resume after a dagger his path
has the "sign of arrest" or "freinage";
- index-ear test: inviting the patient to touch the ear of the same side with
the index finger, the index goes beyond the goal;
- heel-knee test: the patient, in the supine position, is invited to touch the
contralateral knee with the heel: he raises the heel too far, flexes the knee
exaggeratedly and ends by placing the heel on the thighs above the knee;
- test of the glass: the patient is invited to grab a glass full of water and
bring it to his lips and drink: the glass is grabbed badly by the excessively
open hand and sometimes overturned on the table;
- proof of horizontal lines: by drawing horizontal lines that do not have to
exceed a certain vertical line, the line drawn goes beyond this vertical line;
- knee flexion test: the patient's knee is flexed passively from the healthy
side and the patient is asked to take the same angle to the knee of the affected
side: the patient flexes it more.
2) asinergia: the complex movements are decomposed in several times, given the
inability to coordinate the different movements that constitute an act. Thus, if
the patient standing is invited to perform a dorsal flexion of the body or of
the trunk, he loses his stability and falls backwards, as he does not perform a
compensatory flexion of the knees, destined to maintain the equilibrium. During
the march, when the lower limb rises from the ground, the patient does not
perform the compensatory movement of forward bending of the trunk, so that it
tends to fall backwards;
3) adiadocokinesia: inability or difficulty in rapidly performing alternative
antagonist movements.
The patient is made to carry out rapid alternating movements of pronation and
supination of the hands; the cerebellar is not able to perform these movements
with speed, equality and synchronism;
4) kinetic (or intentional) and static tremor. It is a disorder that concerns
the continuity of the contraction. The kinetic tremor is broadly shaken and
appears during the execution of a movement, especially of the upper limbs (for
example, bringing a glass to the lips). Static tremor is a large shock, appears
during the effort required to maintain a position (for example, holding an
object);
5) discretetry, voluntary acts are started late;
6) speech disorders: they are part of the elementary disorders of movement. The
word is slowed down, punctuated, explosive;
7) disorders of writing: with excessively long or excessively short strokes and
therefore very irregular in appearance.
8) disorders of muscle tone: resistance to passive movements has decreased in
cerebellar; hypertonia and passivity depend on delay or absence of contraction
of the antagonist muscles.
This condition is revealed by the Stewart-Holmes rebound test: the patient is
asked to flex his forearms firmly on his arms, while his wrists are held firmly
to oppose the movement. Leaving the grip suddenly, while on the healthy side the
flexion is immediately interrupted and there is an extension movement (rebound),
on the sick side, however, the bending movement continues and the hand goes to
hit the shoulder. The "sign of the fall of the hand" by Gordon Holmes may also
be sought: if the patient is asked to raise his upper limbs upward, a flexion of
the hand is observed.
9) fixation nystagmus: the nystagmus of cerebellar diseases is of the vestibular
type and generally occurs when the gaze is turned to the right and to the left.
Disorders of standing and walking
In maintaining the upright position, coordinated movements from the majority of
the skeletal muscles are necessary so that the vertical passing through the
center of gravity of the body falls on the support base; the same must happen if
we carry a weight on the shoulder or on an arm. Pathological conditions
affecting the pyramidal system, the extrapyramidal motor system, the cerebellar
system, the peripheral neuron, the proprioceptive sensitivity, the muscles, can
be reflected on the ability to maintain the erect station; the ataxic is even
more incapable of standing upright on one leg. Characteristic is the attitude in
some diseases of the nervous system:
- the Parkinsonian is bent forward, with the head bent, forearm and legs
slightly bent;
- the hemiplegic has a characteristic flexion contracture of the upper limb and
extension of the lower limb, with foot in plantar flexion and moved outwards;
- the cerebellar presents a tight position of the head, mostly slightly inclined
on one side and does not stop oscillating.
A) Proof of pushing
When the subject is in a position of attention with the tips of the feet
together, it is pushed gently backwards (exerting pressure on the breastbone) or
forward (exerting pressure on the back). The patient suffering from Parkinson's
disease recedes or advances, stopping only when he meets an obstacle (it is
therefore obtained the impression that he is pursuing his center of gravity)
B)
Romberg's sign
It is a sign of static ataxia. The patient, while being in a position to stand
straight and still, in a position of careful with the tips of the feet together
with open eyes, instead with closed eyes fluctuates strongly and risks falling.
It is characteristic of sensitive ataxia and vestibular ataxia. The cerebellar
is not influenced by the closing of the eyes and does not show the sign of
Romberg.
The ambulation results from a series of coordinated acts that start under the
impulse of the will, but which then continue automatically.
A) Pathological changes in walking The most common types of walking impairment
are:
- non-toxic cerebellar gait: it is the gait that recalls that of the drunk with
considerable irregularity in going; the gait is uncertain in zig-zag, with legs
apart, arms outstretched from the trunk, with oscillations and tendency to fall
from one side or back. This disorder does not change with the closing of the
eyes;
- non-toxic gait of a sensitive (or tabular) type: the patient walks with his
legs apart, lifts the lower limb exaggeratedly (flexing it exaggeratedly at the
knee) and places it heavily on the ground with the heel; walking trying to
maintain balance by observing one's lower limbs; eye closure and darkness
aggravate the ambulatory disorder.
Link on topics:
il paziente con bradicinesia, le cause mediche
il paziente con muscoli flaccidi, che fare e perche'
Il paziente allettato e la sua gestione
Il paziente con tremori
Il paziente con tremori: la cura, evidenze cliniche