Cerebellar Function

Ovid: Pocket Guide and Toolkit to DeJong’s Neurologic Examination

Authors: Campbell, William W.
Title: Pocket Guide and Toolkit to DeJong’s Neurologic Examination, 1st Edition
> Table of Contents > Section H – Coordination and Gait > Chapter 32 – Cerebellar Function

Chapter 32
Cerebellar Function
The cerebellum is tasked
with bringing finesse to the motor system. Although not primarily
involved in the mechanisms for production of muscle power, it is
necessary for normal control and regulation of muscle contraction. The
major function of the cerebellum, from a clinical point of view, is the
coordination of movement. The cerebellum is the portion of the brain
through which the cerebral motor cortex achieves the synthesis and
coordination of individual muscle contractions required for normal
voluntary movements. Without it, movements are gross, uncoordinated,
clumsy, and tremulous, and precise movements become impossible. Lesions
of the cerebellum do not cause weakness, but rather loss of
coordination and inability to gauge and regulate, as Gordon Holmes
said, the “rate, range, and force” of movement. Although motor strength
and power are preserved, active movements are severely compromised.
A major manifestation of cerebellar lesions is ataxia
(Gr. a “without,” taxis “order”); a rough translation is “not orderly.”
The essential feature in ataxia is that movements are not normally
organized. Although the term is a general one, indicating chaotic and
disorganized movement, it is used clinically primarily to refer to the
motor control abnormalities—including incoordination, tremor, and
impaired rapid alternating movements—that occur with cerebellar
lesions. Ataxia is not specific for cerebellar disease, and lesions in
other parts of the nervous system must be excluded before attributing
ataxia to cerebellar disease. Impaired proprioception may cause sensory
ataxia and lesions involving pathways that originate in the frontal
lobe may cause frontal lobe ataxia. Other common manifestations of
cerebellar disease include nystagmus, impaired balance, and difficulty


TABLE 32.1 Clinical Manifestations of Disorders of the Cerebellum (Related to the Different Zones of the Cerebellum)

Zone of Cerebellum

Clinical Manifestation

Possible Disorder

Flocculonodular lobe (archicerebellum)

Nystagmus; extraocular movement abnormalities


Vermis (paleocerebellum)

Gait ataxia

Alcoholic degeneration

Hemisphere (neocerebellum)

Appendicular ataxia

Tumor; stroke


All of the above


Patients with cerebellar dysfunction suffer from various
combinations of tremor, incoordination, difficulty walking, dysarthria,
and nystagmus, depending on the parts of the cerebellum involved (Table 32.1).
Cerebellar disease may also cause hypotonia, asthenia or slowness of
movement, and deviation or drift of the outstretched limbs. Disease
involving the cerebellar connections in the brainstem causes
abnormalities indistinguishable from disease of the cerebellum itself.
When cerebellar ataxia results from dysfunction of the cerebellar
connections in the brainstem there are usually other brainstem signs.
The essential disturbance in cerebellar disease is
dyssynergia. Normally, there is harmonious, coordinated action between
the various muscles involved in a movement so that they contract with
the proper force, timing, and sequence of activation to carry out the
movement smoothly and accurately. Cerebellar disease impairs the normal
control mechanisms that organize and regulate the contractions of the
different participating muscles and muscle groups to insure smooth,
properly coordinated movement. There is a lack of speed and skill in
performing movements that require the coordinated activity of several
groups of muscles or of several movements. The cerebellum is
instrumental in timing the activation of the different muscles involved
in a movement. Lack of integration of the components of the act results
in decomposition of movement—the act is broken down into its component
parts and carried out in a jerky, erratic, awkward, disorganized
manner. The cerebellum is particularly important in coordinating
multi-joint movements.
Dysmetria refers to errors in judging distance and
gauging the distance, speed, power, and direction of movement.
Cerebellar dysfunction leads to loss of the normal collaboration
between agonist and antagonist. When reaching for an object 50 cm away,
the hand shoots out 55 cm, overshooting the target (hypermetria), or
fails to reach the target (hypometria). Hypermetria is more common. The
movement may be carried out too slowly or too rapidly with too much or
too little force. The patient with dysmetria does not make a movement
along a straight line between two points, but erratically deviates from
the intended track.
Agonist-Antagonist Coordination
A disturbance in reciprocal innervation results in a
loss of the ability to stop the contraction of the agonists and rapidly
contract the antagonists to control and regulate movement. Impairment
of the ability to carry out successive movements and to stop one act
and follow it immediately by


diametric opposite causes dysdiadochokinesia, loss of checking
movements, and the rebound phenomenon. Dysdiadochokinesia (or
adiadochokinesia) is a clumsy term (coined by Babinski) that means
inability to make rapid repetitive or rapid alternating movements
(RAMs). The patient with impaired RAMs has difficulty with such tests
as patting the palm of one hand alternately with the palm and dorsum of
the other hand, rapid tapping of the fingers, tapping out a complex
rhythm, or tapping the foot in steady beat. Inability to rapidly
reverse an action also causes impairment of the check response,
producing the Holmes rebound phenomenon (see section on Impaired Check
and the Rebound Phenomenon).

The most common type of cerebellar tremor is an
intention (active, kinetic, or terminal) tremor that is not present at
rest but becomes evident on purposeful movement. In the upper
extremity, when the patient reaches to touch an object there are
irregular, to-and-fro, jerky movements perpendicular to the path of
movement that increase in amplitude as the hand approaches the target.
A postural tremor of the outstretched limbs may also occur, without the
patient reaching for a target. Cerebellar tremor often involves the
proximal muscles. When severe, cerebellar tremor may involve not only
the extremities, but also the head or even the entire body. Severe
cerebellar tremor may at times take on an almost myoclonic character;
some conditions cause both cerebellar ataxia and myoclonus. The tremors
and other movements probably result from disease involving the
cerebellar efferent pathways or their connections with the red nucleus
and thalamus (dentorubraI and dentothalamic pathways, or superior
cerebellar peduncle), and are sometimes referred to as a cerebellar
outflow tremor. A rubral tremor is present at rest but worsens with
action, and probably results from a lesion involving the cerebellar
outflow tracts.
Hypotonia, or muscle flaccidity, with a decrease in
resistance to passive movement, is often seen in cerebellar disease.
Cerebellar dysfunction results in a decrease in the tonic output of the
cerebellar nuclei, causing loss of cerebellar facilitation to the motor
cortex. The muscles are flabby and assume unnatural attitudes; the
parts of the body can be moved passively into positions of extreme
flexion or extension. The stretch reflexes are normal or diminished in
disease limited to the cerebellum. Occasionally, the tendon reflexes
are “pendular.” Tapping the patellar tendon with the foot hanging free
results in a series of to-and-fro movements of the foot and leg before
the limb finally comes to rest. Pendular reflexes are caused by muscle
hypotonicity and the lack of normal checking of the reflex response.
The superficial reflexes are unaffected by cerebellar disease.
Cerebellar disease may also cause a characteristic position of the
extended hand, probably because of hypotonia. The wrist is flexed and
arched dorsally, with the fingers hyperextended, and a tendency toward
overpronation. The hand is similar to that seen in Sydenham chorea. A
cerebellar lesion may cause a decrease in the normal pendular movement
of the affected arm when walking. A decreased arm swing may also occur
with extrapyramidal disorders and with mild hemiparesis. In the
shoulder-shaking test, a cerebellar lesion causes an increase in the
range and duration of swinging of the involved arm, although the
movements may be irregular and nonrhythmic.
Cerebellar disease often affects speech. Articulation
may be slow, ataxic, slurred, drawling, jerky, or explosive in type,
because of dyssynergy of the muscles of phonation. A scanning type of
dysarthria is particularly characteristic of cerebellar disease. The
scanning speech of multiple sclerosis and the staccato speech of
Friedreich ataxia are probably the result of cerebellar dysfunction.


Nystagmus and other disturbances of ocular motility may
occur with lesions of the cerebellum. Nystagmus often indicates
involvement of vestibulocerebellar pathways. The ocular abnormalities
often result from involvement of the connections of the cerebellum with
other centers rather than actual cerebellar dysfunction. Cerebellar
disease may cause gaze paretic nystagmus. The patient is unable to
sustain eccentric gaze and requires repeated saccades to gaze
laterally. With a lesion of one hemisphere the eyes at rest may be
deviated 10 degrees to 30 degrees toward the unaffected side. When the
patient attempts to gaze elsewhere, the eyes saccade toward the point
of fixation with slow return movements to the resting point. The
movements are more marked and of greater amplitude when the patient
looks toward the affected side. When a tumor of the cerebellopontine
angle is present, the nystagmus is coarse on looking toward the side of
the lesion and fine and rapid on gaze to the opposite side (Bruns
nystagmus). Other ocular motility disturbances seen with cerebellar
disease include skew deviation, ocular dysmetria, ocular flutter,
opsoclonus, and saccadic intrusions. Rebound nystagmus is a type of
nystagmus that may be unique to cerebellar disease; the fast component
is in the direction of lateral gaze, but transiently reverses direction
when the eyes come back to primary position.
Other Abnormalities
Abnormalities of posture and gait with abnormal
attitudes and spontaneous deviation of the head and parts of the body
may be seen in cerebellar disease. In unilateral cerebellar disease
there may be deviation of the head and body toward the affected side,
with past pointing of the extremities toward the affected side. When
standing, there is an inclination to fall, and when walking a tendency
to deviate, toward the side of the lesion. The outstretched extremities
deviate laterally, toward the affected side. There may be a decrease or
absence of the normal pendular movement of the arm in walking. In
midline, or vermis, lesions the patient may not be able to stand erect
and may fall either backward or forward. The gait is staggering,
reeling, or lurching in character, without laterality.
Clinical tests for cerebellar dysfunction are basically
designed to detect dyssynergia, decomposition of movement, and
dysmetria. The combination of incoordination, awkwardness, errors in
the speed, range, and force of movement, along with dysdiadochokinesia
and intention tremor is referred to as cerebellar ataxia. Simple
observation can be as informative as a detailed clinical examination.
Watching as the patient is standing, walking, dressing and undressing,
buttoning and unbuttoning clothing, and tying shoelaces may reveal
tremor, incoordination, clumsiness, and disturbed postural fixation.
The patient may be asked to write, use simple tools, drink from a
glass, and trace lines with a lightweight pen while no support is given
at the elbow. The examination of infants and children may be limited to
simple observation, noting the child’s ability to reach for and use
toys and objects. Tests for coordination may be divided into those
concerned with equilibratory and nonequilibratory functions.
Equilibratory Coordination
Equilibratory coordination refers to the maintenance of
balance and the coordination of the body as a whole. The examination of
station and gait assesses equilibratory coordination; these are
discussed further in Chapter 44.
Nonequilibratory Coordination
Tests of nonequilibratory coordination assess the
patient’s ability to carry out discrete, oftentimes relatively fine,
intentional movements with the extremities. Although these are
primarily tests of coordination, other neural systems must be intact
for normal performance. It is important to consider


in judging coordination, and to allow for the normal slight clumsiness
of the non-dominant side. Patients who are fatigued or sedated may have
incoordination that is not normal for the individual. Fine motor skills
may also be assessed functionally by asking the patient to do such
things as thread a needle, pick up a pin, string beads, pour water, or
draw circles.

The Finger-to-Nose (Finger-Nose-Finger) Test
There are several variations on the theme of having the
patient touch his index finger to his nose, all of which will be
included as the finger-to-nose (FTN) test. All may be carried out with
the patient lying, seated, or standing. The patient extends the arm
completely and then touches the tip of the index finger to the tip of
the nose, slowly at first, then rapidly, with the eyes open and then
closed. The examiner may place the outstretched extremity in various
positions, and have the test carried out in different planes and from
various angles. The patient may be asked to touch the tip of his index
finger to his nose, then touch the tip of the examiner’s finger, and
then back to the tip of his nose. It is helpful to demonstrate the
requested movement, lest the patient make some odd interpretation of
the verbal request; an occasional patient will attempt to put his index
finger on the examiner’s finger without removing it from his own nose.
The examiner’s finger may be moved about during the test, and the
patient asked to try to touch the moving target as the finger is placed
in different locations at different distances, and to move both slowly
and quickly. The examiner may pull his finger away and make the patient
chase it; fully extending the arm in this way can bring out mild
intention tremor.
During these movements note the smoothness and accuracy
with which the act is executed, and look for oscillations, jerkiness,
and tremor. An intention tremor becomes more marked, coarse, and
irregular as the finger approaches the target. There may be little
tremor during the midrange of the movement, but near the end the tremor
erupts; when the finger contacts the target the tremor stops. In
cerebellar ataxia, the difficulty may vary from slight incoordination,
with a blundering type of movement, to wild oscillations causing
complete inability to execute the act. A patient with severe
appendicular ataxia may not be able to touch hand to head, much less
finger to nose.
With dysmetria the patient may stop before he reaches
his nose, pause and then complete the act slowly and unsteadily, or
overshoot the mark and bring the finger to the nose with too much speed
and force. With dyssynergy the act is not carried out smoothly and
harmoniously; there may be irregular stops, accelerations, and
deflections, or the movement may disintegrate into its component parts.
Performing the FTN test against slight resistance may cause mild ataxia
to become more obvious, or latent ataxia evident. The examiner may
apply resistance by placing his fingers against the patient’s forearm
and exerting slight pressure as the patient moves his arm toward the
nose, or by placing a long rubber band around the patient’s wrist and
pulling gently on it during the test. Another test is to have the
patient draw a line, starting and then stopping at fixed points. He may
have difficulty in starting at the correct point and may either stop
short of the second point or overshoot the mark. This may also
demonstrate tremor, with side-to-side oscillations along the intended
tract. The patient with cerebellar disease may have macrographia, using
large characters that become larger across the page, the opposite of
the writing disturbance seen in Parkinson disease.
In the finger-to-finger (fingertips in the midline)
test, the patient abducts the arms widely to the horizontal and then
brings in the tips of the index or middle fingers through a wide arc to
touch them exactly in the midline. This is done slowly and rapidly,
with the eyes first open and then closed. With unilateral cerebellar
disease the finger on the involved side may fail to reach the midline,
and the finger on the normal side may cross the midline to reach it.
Also, the arm on the affected side may sag or rise, causing the finger
on that side to be below or above the one on the normal side.


In hysteria or malingering there may be bizarre
responses of various types. The patient may act as if unable to touch
the finger to the nose, or circle around it with widespread, wandering
movements but eventually touch the very tip. Or the patient may
repeatedly but precisely touch some other part of the face, implying
there is no loss of sensation or coordination.
Similar tests may be used to evaluate the lower
extremities. In the heel-to-shin (heel-kneeshin/toe) test, the patient
is asked to place the heel of one foot on the opposite knee, tap it up
and down on the knee several times, push the point of the heel (not the
instep) along the shin in a straight line to the great toe, and then
bring it back to the knee. The patient with cerebellar disease is
likely to raise the foot too high, flex the knee too much, and place
the heel down above the knee. The excursions along the shin are jerky
and unsteady. With sensory ataxia, the patient may have difficulty
locating the knee with the heel, groping around for it; there is
difficulty keeping the heel on the shin, and it may slip off to either
side while sliding down the shin. In the toe-to-finger test, the
patient tries to touch his great toe, knee bent, to the examiner’s
finger. If there is dysmetria, he will undershoot or overshoot the
mark; intention tremor and oscillations may also be evident. The
patient may be asked to draw a circle or a figure eight with his foot,
either in the air or on the floor; in ataxia the movement will be
unsteady and the figure irregular.
Rapid Alternating Movements
With dysdiadochokinesia, one act cannot be immediately
followed by its diametric opposite; the contraction of one set of
agonists and relaxation of the antagonists cannot be followed
immediately by relaxation of the agonists and contraction of the
antagonists. Patients with cerebellar ataxia may have great difficulty
making these kinds of movements. A common test for dysdiadochokinesia
is to have the patient alternately pronate and supinate his hands, as
in patting alternately with the palm and dorsum of the hand on the
thigh or on the palm or dorsum of the other hand, or imitating screwing
in a lightbulb or turning a doorknob. The movements are performed
repetitively and as rapidly as possible. Any movement involving
reciprocal innervation and alternate action of agonists and antagonists
can be used, such as: alternate opening and closing of the fists,
quickly flexing and extending individual fingers, touching the tip of
the index finger to the tip or extended interphalangeal joint of the
thumb, or patting rapidly against a table top with hand or fingertips.
A good test is to have the patient touch the tip of his thumb with the
tip of each finger rapidly and in sequence—starting with the index
finger and proceeding to the little finger, repeating with the little
finger and going to the index finger, and so forth. Another good test
is to have the patient tap out a simple rhythm with each hand (e.g.,
1-2-3/pause in steady beat), and then a more complex but familiar
rhythm (e.g., “Happy Birthday” song). Testing RAMs in the lower
extremity is much more limited. The patient may be asked to pat the
foot steadily, against the floor if standing, against the examiner’s
palm if recumbent, or to repetitively touch the heel up and down to the
knee if supine. Rapid alternating movements of the tongue may be tested
by having the patient move the tongue in and out or from side to side
as rapidly as possible.
In all of these tests, note the rate, rhythm, accuracy,
and smoothness of the movements. In patients with ataxia, the RAMs are
either carried out slowly and hesitantly, with pauses during transition
between the opposing motions, or unsteadily and irregularly, with loss
of rhythm. There may be a rapid fatigability: The movements may be
executed satisfactorily in the beginning, but after a few attempts they
become awkward and clumsy. The two extremities are usually compared,
but patients with bilateral abnormalities are common and the examiner
must rely on experience or use another control. Demonstrating the
movements to the patient provides an opportunity for the examiner to be
the control. For some maneuvers, such as rapid, repetitive finger
movements the two extremities can be examined simultaneously and one
side compared with the other. Simultaneous testing may also cause
accentuation of the abnormality on the affected side.


Impaired Check and the Rebound Phenomenon
Checking movements involve contraction of the
antagonists after a load is unexpectedly removed during strong
contraction of the agonist. The agonists must immediately relax and the
antagonists must contract to provide braking after the sudden release
of resistance. Since cerebellar dysfunction causes impairment of the
reciprocal relationship between agonist and antagonist, patients may
have impairment of the checking response.
In the Holmes (Stewart-Holmes) rebound test, the patient
holds the arm adducted at the shoulder and flexed at the elbow, with
the forearm supinated and the fist firmly clenched. The elbow may rest
on a table or be held unsupported close to the body. The examiner pulls
on the wrist, and the patient strongly resists the examiner’s attempt
to extend the elbow. The examiner then suddenly releases his grip on
the wrist. Normally, with the sudden unloading the contraction of the
elbow flexors immediately ceases and is rapidly followed by contraction
of the elbow extensors to arrest the sudden flexion movement and stop
the patient from hitting himself. The normal patient is able to control
the unexpected flexion movement of the elbow. In cerebellar disease,
when the strongly flexed extremity is suddenly released the patient
cannot stop the flexor contraction and engage the extensors to stop the
elbow movement. Because of loss of the checking response, the fist
flies up to the shoulder or mouth, often with considerable force. The
examiner’s free arm should be placed between the patient’s fist and
face to block the blow. The prevalent description of this as the Holmes
rebound phenomenon is not precisely correct. Stewart and Holmes used
rebound to refer to the jerk back in the opposite direction, the
recoil, on release of the restraint. The rebound phenomenon is present
normally and exaggerated in spastic limbs. It is the absence of rebound
(usually accompanied by impaired checking) in limbs affected by
cerebellar disease that is abnormal. The rebound test may be carried
out in other ways. Elbow extension against resistance may be tested
instead of flexion. With both arms outstretched in front of the
patient, the examiner may press either down or up on them as the
patient resists and then suddenly lets go. This allows comparison of
the rebound phenomenon and loss of checking movements on the two sides.
In the lower extremities, rebound can be tested by sudden release after
the patient has been resisting either flexion or extension at the knee,
hip, or ankle. Impaired checking and the rebound phenomenon are not
invariably present in cerebellar disease, and may sometimes be present
in normal limbs or even exaggerated in spastic limbs. An abnormal
rebound test unilaterally is more significant than when present
bilaterally. In the arm-stopping test, the patient holds both arms
overhead or by his sides, the examiner holds his arms outstretched
horizontally, and then the patient tries to quickly bring his arms up
or down so that his fingertips are at the exact same level as the
examiner’s. With a unilateral hemispheric lesion, the good arm will
stop on target, the affected arm often overshoots and then corrects in
the opposite direction, oscillating around the target before eventually
coming to rest.
Deviation and Past Pointing
Patients with cerebellar disease often have difficulty
maintaining normal alignment of the limbs or body when performing a
task such as holding the arms outstretched or walking, especially with
eyes closed. The patient may miss when trying to reach out to touch a
target (past pointing), drift to one side when walking eyes closed, or
have drift of the outstretched arm. Similar findings may occur with
vestibular lesions.
To perform the traditional test for past pointing, the
patient and examiner should be facing, either seated or standing, the
outstretched upper extremity of each held horizontally with the index
fingers in contact. The patient raises his arm to a vertical position,
finger pointed directly upward, and then returns to horizontal to again
touch the examiner’s finger. The maneuver should be tried a few times
with the eyes open and then executed with the eyes closed. The arms may
be tested sequentially or simultaneously. The test is less commonly
done with the patient raising the arm from


up to the horizontal. Normally, the patient will return to the starting
position fairly accurately, without any drift or deviation. In
labyrinthine disease or with a cerebellar hemispheric lesion, the arm
will deviate to the involved side on the return track, more so with the
eyes closed. This deviation is called past pointing. A simpler way to
test for past pointing is to have the patient close his eyes while
doing the finger-nose-finger test. With eyes open the pointing is
accurate, but with eyes closed the patient points off to the side of
the target. Repeating the test several times may produce greater
deviation. With severe lesions, past pointing may occur even with eyes
open. The pattern is different in vestibular as opposed to cerebellar
past pointing. In vestibular disease, past pointing occurs with both
upper extremities toward the involved side; in unilateral cerebellar
disease past pointing occurs toward the side of the lesion, but only in
the ipsilateral arm.

A cerebellar lesion may also cause drift of the
outstretched upper extremities. Three types of drift may occur when the
patient attempts to hold the arms outstretched with eyes closed:
pyramidal drift, parietal drift, and cerebellar drift. In pronator
drift (Barré sign) due to a pyramidal lesion, the arm sinks downward
and there is accompanying pronation of the forearm. In parietal drift,
the arm usually rises and strays outward (updrift). With cerebellar
drift the arm drifts mainly outward, either at the same level, rising
or less often sinking. Testing is done with arms outstretched and eyes
closed. With disease involving one cerebellar hemisphere, the arm
drifts toward the side of the lesion. The deviation may be accentuated
by having the patient raise and lower the arms several times, or by
tapping the patient’s outstretched wrists. Tapping on the wrists may
also create an up-and-down oscillation because of impaired checking, so
that the arm swings up and down a few times, and gradually drifts
laterally and often upward.
Position-holding can also be tested in the lower
extremities. The patient, lying supine, raises the legs one at a time.
When there is ataxia, the leg cannot be lifted steadily or in a
straight line. There may be adduction, abduction, rotation,
oscillations, or jerky movements from one position to another. When the
limb is lowered, the patient may throw it down heavily and it may not
return to its original position beside its mate but may be deviated
across it or away from it. When the seated patient extends the legs
without support and attempts to hold them steady, a unilateral
cerebellar lesion may cause oscillations and lateral deviation of the
ipsilateral extremity. The extended supported leg may show an increased
range and duration of pendulousness when released or given a brisk
push. If the prone patient bends the knees and tries to maintain the
shins vertically, there may be marked oscillations and lateral
deviation of the leg on the side of the lesion.
Deviation and drift may also occur when the patient
tries to walk with eyes closed. As in vestibulopathy, the patient
drifts to the side of the lesion. Walking back and forth with eyes
closed may reveal a “compass” or “star” gait due to deviation toward
the involved side. When walking around a chair, the patient shows a
tendency to fall toward the affected side.
Cerebellar disease may affect all or only a specific
part of the cerebellum. There are two clearly defined cerebellar
syndromes: a midline or vermis syndrome, and a lateral or hemispheric
syndrome. With the vermis, or midline, syndrome the outstanding
symptoms are abnormalities of station and gait, with abnormalities
ranging from slight widening of the base on walking in mild disease
(gait ataxia), to total inability to sit or walk in severe disease.
Disease of the cerebellar hemispheres produces appendicular ataxia,
disturbance in coordination of the ipsilateral extremities, the arm
more than the leg. The primary clinical manifestations of dysfunction
of the FN lobe or its connections are disturbances of equilibrium;
nystagmus, often positional; and other abnormalities of extraocular
movement. There is no limb ataxia. Table 32.1 summarizes the clinical manifestations of disease of these parts of the cerebellum.
The manifestations of cerebellar disease differ markedly
in severity, depending upon the acuteness or chronicity of the process.
The ability of the nervous system to compensate for a cerebellar lesion
can be remarkable. If the lesion is acute, the symptoms are profound;
if it is slowly progressive,


are much less severe. There may be considerable recovery from an acute
lesion. If a lesion develops insidiously, there may be extensive
involvement of the hemispheres without much in the way of clinical
findings. The neural plasticity and compensation are such that some
patients with little remaining cerebellar tissue can eventually
function quite well. The symptoms of cerebellar disease are similar
regardless of the etiology of the disease process, and whether the
lesion is congenital or acquired.

Midline Syndrome
The vermis is important in the control of axial
structures, or those that are bilaterally innervated; vermian lesions
primarily affect midline functions, such as walking and coordination of
the head and trunk. A patient with mild vermian disease has gait
ataxia. The base is widened, tandem gait is particularly difficult, and
there may be decompensation on turning. The Romberg test is
negative—the imbalance does not worsen significantly with eyes closed.
With severe dysfunction of the vermis, there may be gross postural and
locomotor disturbances of the entire body. There is no lateralization,
and the tendency to fall may be either backward or forward. The gait is
wide-based and characterized by swaying and staggering; the patient may
reel in a drunken manner to either side. With truncal ataxia there is
swaying and unsteadiness when standing, and the patient may be unable
to maintain an upright position. There may be loss of the ability to
remain erect when seated, or to hold the neck and head steady and
upright; when severe, the standing and sitting balance disturbance
leads to constant, to-and-fro swaying, nodding, and weaving movements
of the head and trunk when the patient is upright known as titubation.
The head movements in titubation are primarily anteroposterior
(yes-yes) at 3 to 4 Hz. Vermis dysfunction causes little or no
abnormality of the extremities, especially the upper extremities,
although all coordinated movements may be poorly performed. Muscle tone
and reflexes are normal. Nystagmus may be present, but is usually not
marked. Ocular dysmetria, rebound nystagmus, and pursuit abnormalities
may also occur. Lesions involving the vermis may cause upbeat
nystagmus. Dysarthria is often present. There is sometimes an abnormal
rotated or tilted head posture.
Common causes of a midline cerebellar syndrome are
alcoholic cerebellar degeneration and medulloblastoma. Alcohol
preferentially poisons the vermis, leading to a characteristic syndrome
of gait ataxia with sparing of the limbs. Such patients may have no
demonstrable lower-extremity ataxia while lying supine, yet be totally
unable to walk. Unwary examiners may conclude such findings represent
hysteria. Medulloblastomas occur most often in the cerebellar vermis.
Hemispheric Syndrome
With a lesion involving one cerebellar hemisphere, the
manifestations are appendicular rather than axial. Cerebellar
hemispheric deficits are unilateral and ipsilateral to the lesion, as
the pathways are uncrossed (or, more correctly, double crossed). There
is a disturbance of skilled movements of the extremities, with ataxia,
dysmetria, dyssynergy, dysdiadochokinesia, and hypotonicity affecting
the arm and hand more than the leg and foot. Distal movements are
affected more than proximal and fine movements more than gross ones.
Movements are performed irregularly, and there may be intention tremor
or other hyperkinesias if the dentate nucleus or its efferent pathways
are involved.
Posture and gait are not impaired as severely as in the
vermis syndrome, but abnormalities do occur. There may be swaying and
falling toward the side of the lesion. The patient may be able to stand
one-legged using the contralateral but not the ipsilateral foot. He may
be unable to bend his body toward the involved side without falling.
The abnormalities often resemble those of a unilateral vestibular
lesion. On walking, there may be unsteadiness, with deviation or
rotation toward the involved side. There may be drift and past pointing
toward the involved side. Dysarthria may occur, although disturbances
of articulation are not as severe as in vermis lesions. Nystagmus is a
common finding, usually horizontal but sometimes rotatory. It is
usually more prominent when looking toward the side of the lesion.
Common causes of a cerebellar hemispheric syndrome include cerebellar
astrocytoma, multiple sclerosis, and lateral medullary stroke.


TABLE 32.2 Associated Findings Helpful in Distinguishing Sensory from Cerebellar Ataxia

Sensory Ataxia

Cerebellar Ataxia

Sensory loss, especially for joint position and vibration

Nystagmus, ocular dysmetria, and other eye movement abnormalities

Steppage gait

Reeling, ataxic gait

Decreased reflexes

Other signs of cerebellar disease (dyssynergia, dysmetria, dysdiadochokinesia, hypotonia, rebound, impaired check response)

Diffuse Cerebellar Dysfunction
Some conditions affect the cerebellum diffusely, causing
midline and bilateral hemispheric abnormalities. Patients may have
nystagmus, gait and truncal ataxia, and appendicular incoordination.
Etiologies include the hereditary spinocerebellar ataxia syndromes,
drugs (especially phenytoin), toxins, and paraneoplastic cerebellar
Sensory Ataxia
Incoordination may also result from a lack of
proprioceptive input from the limbs. Sensory ataxia results from
peripheral nerve disease affecting primarily sensory fibers, pathology
involving the dorsal root ganglia, dorsal roots or posterior columns of
the spinal cord, interruption of the proprioceptive pathways in the
brainstem, or disease of the parietal lobe. Incoordination due to
sensory ataxia can closely mimic that of cerebellar ataxia (Table 32.2).
With cerebellar ataxia, it makes little difference whether the
patient’s eyes are open or closed. In sensory ataxia, performance is
not normal with eyes open, but worsens markedly with eyes closed. The
different components of the abnormality may behave slightly differently
when visual input is removed. Some of the tremor in sensory ataxia is
due to visually guided voluntary corrections of deviations from the
intended track. Because of loss of appreciation of limb position in
space, with eyes closed the patient may be unable to find his nose or
the examiner’s finger, but the tremor may actually abate because the
patient cannot see that a deviation is occurring and does not attempt
to correct it. He may be wildly off target but move in a straighter
line. The distinction between cerebellar and sensory ataxia is also
made by the associated findings (Table 32.2).
Other Abnormalities
There are many potential causes for a lack of
coordination of movement. All of the levels of the motor system are
involved in performing smooth and accurate movement. Weakness of any
origin may interfere with skill and precision. Abnormalities of tone of
any type may interfere with coordination. Diseases of the
extrapyramidal system may impair motor control because of rigidity,
akinesia or bradykinesia, lack of spontaneity, and loss of associated
movements. A corticospinal tract lesion may cause jerkiness and
clumsiness of movement, loss of motor control, and poor integration of
skilled acts. Nonorganic illness may cause difficulty with coordination
simulating true ataxia. Hyperkinetic movement disorders may cause
irregularity in the timing and excursion of successive movements.
Proprioceptive abnormalities may impair motor performance. To always
attribute ataxia to cerebellar disease is an oversimplification, since
many conditions can cause incoordination and clumsiness. Often the
cause is multifactorial. A good general rule is to avoid drawing
conclusions about the meaning of “cerebellar signs” in the face of any
significant degree


weakness, spasticity, rigidity, or sensory loss. When the examination
shows no other abnormalities, incoordination and awkwardness of
movement are usually due to cerebellar disease.

Frontal lobe ataxia refers to disturbed coordination due
to dysfunction of the contralateral frontal lobe; it may resemble the
deficits due to abnormalities of the ipsilateral cerebellar hemisphere.
Frontal lobe ataxia results from disease involving the
frontopontocerebellar fibers en route to synapse in the pontine nuclei.
Frontal lobe lesions may produce other abnormalities, such as
hyperreflexia, increased tone, and pathologic reflexes; while purely
cerebellar lesions typically cause hypotonia, diminished or pendular
reflexes, and no pathologic reflex responses. Pressure on the brainstem
by a cerebellar mass lesion may cause corticospinal tract findings that
can confuse the picture. Bruns ataxia refers to a gait disturbance seen
primarily in frontal lobe lesions.

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