Definition

The principal signs of cerebellar dysfunction are the following:

Ataxia: unsteadiness or incoordination of limbs, posture, and gait. A disorder of the control of force and timing of movements leading to abnormalities of speed, range, rhythm, starting, and stopping.

Hypotonia: normal resting muscle tension is reduced, leading to decreased muscle tone and abnormal positions of parts of the body.

Tremor: an intention tremor of the hand on purposive movement is the most common, with coarse, rapid, side-to-side oscillations that increase as the movement goal is approached. Resting tremors of the limbs, head, and trunk can occur. At times, paroxysms of these tremors are severe enough to shake the entire bed and delude the unwary physician into suspecting seizure activity.

Gait: the station or manner of standing is abnormal; the legs are apart and there is swaying of the body. "The patient staggers, reels, and lurches on walking.

Ocular motor abnormalities: saccadic dysmetria, impaired smooth tracking, fixation abnormalities, and various forms of nystagmus (see below).

Technique

Have the patient sit on the side of a bed or table. Note the position of the limbs; hypotonia can produce bizarre positions. The head can be deviated to one side. Look for resting tremors of the limbs and trunk. At times, these can be of such severity to cause the head to bob, or titubate.

Basic Science

The field of cerebellar anatomy and physiology is one of the most complex and rapidly advancing areas in the neurosciences. In this section we give only the briefest background information, focusing primarily on some clinical correlations.

Anatomically the cerebellum can be divided transversely into three lobes, anterior, posterior, and flocculonodular, and longitudinally into a midline vermis and two lateral hemispheres (Larsell's nomenclature) (Figure 69.1). The simplified scheme of cerebellar organization given in Table 69.1 is modified from DeMyer (1974). There are exceptions to some of the generalizations.

Figure 69.1

Anatomy and organization of the cerebellum. Modified from DeMyer W, Technique of the neurological examination: a programmed text, 2nd ed., McGraw-Hill, 1974; and Brodal A, Neurological anatomy, 2nd ed., Oxford University Press, 1969, using O Larsell's (more...)

Table 69.1

A Simplified Scheme of Cerebellar Anatomy.

The cerebellum can be divided into three longitudinal zones on the basis of afferent connections:

1. Vestibulocerebellum: afferents from vestibular nuclei
2. Spinocerebellum: afferents from the spinal cord
3. Pontocerebellum or corticocerebellum: afferents from cerebral cortex via pontine nuclei

These divisions project onto the cerebellar nuclei and have efferent connections as outlined in the scheme. These three subdivisions do not exactly correspond to the anatomical divisions; there is considerable overlap.

DeMyer (1974) has put the function of the cerebellum lucidly by pointing out that the cerebellum probably evolved out of the vestibular nuclei. Using information provided by the vestibular system and other areas, the cerebellum equilibrates the contractions of axial musculature so that the eyes and head are properly positioned. In higher animals the cerebellum takes on the additional role of seeing to the smooth performance of voluntary movements by the limbs, working closely with the cerebrum. Thus the cerebellum, "sitting astride the vestibular nuclei," receives on the one hand information from the proprioceptive system, and on the other, information about commands the cerebral cortex is sending to muscles. The cerebellum sees to it that the movements are performed in a smooth, coordinated fashion, receiving constant feedback about what is actually happening.

Information as to what is happening in the muscles comes from muscle spindles, tendon organs, touch and pressure receptors, and from the labyrinth. These afferent impulses converge on the Purkinje cells of the spinocerebellar and vestibulocerebellar portions of the cerebellar cortex (see Figure 69.1), either directly or after synapse on granule cells. Efferent output from the Purkinje cells goes to the cerebellar nuclei (dentate, fastigial, and interpositus) and thence to the spinal cord (and therefore the lower motor neurons), vestibular nuclei, or cerebral cortex.

Interrelationships with the cerebral cortex are complex. Basically each area of the cerebral cortex that sends efferents to the cerebellum in turn gets efferents from that area of the cerebellum. The pathways from the cerebral cortex to the cerebellum can be divided into two groups (Brodal, 1969):

1. Routes via the inferior olive, pontine nuclei, and red nucleus, which show a precise topical organization.
2. Routes via the reticular nuclei principally. These nuclei are diffusely organized and thus can integrate impulses from many different sources before they reach the cerebellum.

Cerebellar efferents to the cortex go from the dentate nucleus mostly to the nucleus ventralis lateralis of the thalamus, thence to the cortex. Efferents from the cerebral cortex to the cerebellum go to the contralateral cerebellar hemisphere. Thus the right cerebellar hemisphere ultimately receives afferents from the right side of the body and the left cerebral cortex, and sends efferents to the same locations.

The cerebellum exerts its influence on motor activity via the cerebral cortex. It also directly influences the gamma fiber systems at the spinal cord level, thus influencing postural tone and reflexes. The nature of the cerebellar influence is still incompletely understood.

There are many problems with localization of cerebellar symptoms. The generalizations in Table 69.2 are crude but helpful.

Table 69.2

Localization of Cerebellar Symptoms.

Clinical Significance

There are a variety of clinical signs in cerebellar disease (Table 69.3). These signs have been studied in detail recently (Gilman, 1986; Gilman, Bloedel, and Lechtenberg, 1981).

Table 69.3

Clinical Signs of Cerebellar Disease.

Stance and gait abnormalities are the most common clinical signs. They reflect disease of the midline zone of the cerebellum. There is a broad-based stance with truncal instability during walking, causing falls to either side. The steps are irregular, and the feet may be lifted too high. Gait ataxia without limb impairment, occurring most commonly with alcohol damage and nutritional deficiency, indicates damage to the anterior superior vermis. Flocculonodular lesions can also produce stance and gait abnormalities. Tandem walking is often the earliest abnormality, and this maneuver is most severely affected.

Titubation consists of a rhythmic body or head tremor. There is a rotatory or rocking or bobbing movement. Clinically this has not turned out to have localizing value with respect to the part of the cerebellum involved.

The head can be rotated, or tilt to one side or the other. As with titubation, this does not have useful localizing value.

Oculomotor disturbances in cerebellar disease have been worked out in detail in the "pure" cerebellar degenerations (Leigh and Zee, 1983; Zee, 1984). The most frequent abnormalities include dysmetric saccades, fixation abnormalities, impaired smooth pursuit, postsaccadic drift, gaze-evoked nystagmus, rebound nystagmus, downbeat nystagmus, and positional nystagmus. Saccadic dysmetria most likely indicates dysfunction of the dorsal vermis and fastigial nuclei. The function of these structures is to control saccade amplitude. The vestibulocerebellum (flocculus) acts to provide stabilization of the retinal image, with dysfunction producing impaired smooth tracking, impaired fixation suppression of caloric nystagmus, and postsaccadic drift. (Also see Chapter 60, Cranial Nerves III, IV, and VI.)

Decomposition of movement occurs with disease of the lateral zones of the cerebellum. This is reflected in difficulty with both simple and compound movements. Movement initiation and termination is affected.

Dysmetria is a trajectory disturbance; placement falls short of or extends beyond the initial goal, as in the finger to nose test. The heel–knee–shin test also demonstrates error in placement, as well as force. The lateral zone of the cerebellum is felt to be responsible for normal placement.

Repetitive movements, such as hand patting, are affected with dysfunction of the lateral zone of the cerebellum. The result is dysdiadochokinesis. Disorder of the rhythm of rapid alternating movements is known as dysrhythmokinesis. Disorders of the basal ganglia and corticospinal system can produce similar types of dysfunction.

Ataxia is the lack of smoothly coordinated movements. This incoordination is chiefly the combined result of dysmetria and decomposition of movement. Movements are imprecise, halting, awkward, and clumsy. Disease of the lateral cerebellar hemispheres causes limb ataxia.

Impaired check and excessive rebound are common signs in cerebellar disease. The patient, with eyes closed, is unable to return a limb that has been tapped and displaced to its original position. Overshoot occurs.

A static tremor, originating at the shoulder, can be brought out by having the patient hold outstretched arms parallel to the floor. A kinetic tremor (or intention tremor) is brought out by the finger to nose and heel to shin tests. It involves the proximal musculature. These tremors usually indicate disease of the lateral zone of the cerebellum on the ipsilateral side.

Dysarthria often occurs in severe cerebellar disease. In a sense, it is ataxia of speech. Articulation is uneven, words are slurred, and variations in pitch and loudness occur. Rhythm changes are prominent. Charcot applied the term "scanning speech" to a pattern heard in cerebellar disease; enunciation is difficult, words are produced slowly and in a "measured" fashion.

Muscle tone abnormalities in cerebellar disease were first described by Gordon Holmes in the 1920s. Hypotonia and pendular deep tendon reflexes are seen. These abnormalities are seen easily when there is unilateral cerebellar disease.

The cerebellum can be involved in a wide variety of systemic diseases, in addition to mass lesions and congenital afflictions. Alcoholism and remote cancer produce a cerebellar syndrome that at least initially begins within the anterior lobe and produces ataxia. Lead, mercury, dilantin, and other toxic or therapeutic agents can cause cerebellar degeneration. Various viral infections and hypoxia can produce prominent cerebellar involvement. Vascular disease can produce involvement of the cerebellum directly or by involvement of the cerebellar peduncles in the brainstem. Examples include the posterior inferior artery syndrome, the superior cerebellar artery syndrome, and the anterior inferior cerebellar artery syndrome. Cerebellar infarction and hemorrhage are other frequent manifestations of cerebrovascular disease. Common neoplasms include metastases, astrocytoma, medulloblastoma, angioblastoma, and acoustic neuroma.

Note that this chapter has not been concerned with ataxia due to involvement of the posterior columns of the spinal cord, the functions of which must be tested before considering ataxia to be of cerebellar origin.

References

1. Brodal A. Neurological anatomy. 2nd ed. New York: Oxford University Press, 1969;255–303.
2. DeMyer W. Technique of the neurological examination: a programmed text. 2nd ed. New York: McGraw-Hill, 1974;237–58.
3. Dow R, Moruzzi G. The physiology and pathology of the cerebellum. Minneapolis: University of Minnesota Press, 1958.
4. Gilman S. Cerebellum and motor dysfunction. In: Asbury AK, McKhann GM, McDonald WI, eds. Diseases of the nervous system. Philadelphia: W.B. Saunders, 1986.
5. Gilman S, Bloedel JR, Lechtenberg R. Disorders of the cerebellum. Philadelphia: FA Davis, 1981.
6. Holmes G. The cerebellum of man. Brain. 1939;62:1–30.
7. Ito M. The cerebellum and neural control. New York: Raven Press, 1984.
8. Leigh RJ, Zee DS. The neurology of eye movements. Philadelphia: FA Davis, 1983.
9. Zee DS. New concepts of cerebellar control of eye movements. Otolaryngol Head Neck Surg. 1984;92:59. [PubMed: 6422417]