Clinical Neurology for Psychiatrists, 6th Edition

FIGURE 2-11 n This young man, who has a multiple sclerosis
(MS) plaque in the right cerebellar hemisphere, has a rightsided
intention tremor. During repetitive finger-to-nose movements,
as his right index finger approaches his own nose and
then the examiner’s finger, it develops a coarse and irregular
path. This irregular rhythm is called dysmetria.
FIGURE 2-12 n In the heel-to-shin test, the patient with the
right-sided cerebellar lesion in Figure 2-11 displays limb
ataxia as his right heel wobbles when he pushes it along the
crest of his left shin.
use uneven force, move irregularly, and lose the alternating
pattern.
Damage to either the entire cerebellum or the vermis
alone causes incoordination of the trunk (truncal ataxia).
It forces patients to place their feet widely apart when
standing and leads to a lurching, unsteady, and widebased
pattern of walking (gait ataxia) (Table 2-3 and
Fig. 2-13). A common example is the staggering and
reeling of people intoxicated by alcohol or phenytoin.
Extensive damage of the cerebellum also causes
scanning speech, a variety of dysarthria. Scanning
speech, which reflects incoordination of speech production,
is characterized by poor modulation, irregular
cadence, and inability to separate adjacent sounds.
Dysarthria—whether from cerebellar injury, bulbar or
pseudobulbar palsy, or other neurologic conditions—
should be distinguishable from aphasia, which is a
language disorder that stems from dominant cerebral
hemisphere injury (see Chapter 8).
Central Nervous System Disorders 13
FIGURE 2-13 n This man, a chronic alcoholic, has developed
diffuse cerebellar degeneration. He has a typical ataxic gait:
broad-based, unsteady, and uncoordinated. To steady his
stance, he stands with his feet apart and pointed outward.
Before considering the illnesses that damage the
cerebellum, physicians must appreciate that the cerebellum
undergoes age-related changes that appear
between ages 50 and 65 years in the form of mildly
impaired functional ability and abnormal neurologic
test results. For example, as people age beyond 50
years, they walk less rapidly and less sure-footedly.
They begin to lose their ability to ride a bicycle and
to stand on one foot while putting on socks. During a
neurologic examination they routinely tend to topple
when walking heel-to-toe, that is, performing the
‘‘tandem gait’’ test.
Illnesses that Affect the Cerebellum
The illnesses that are responsible for most cerebral
lesions—strokes, tumors, trauma, AIDS, and MS—
also cause most cerebellar lesions. The cerebellum is
also particularly vulnerable to toxins, such as alcohol,
toluene (see Chapters 5 and 15), and organic mercu ry;
medications, such as phenytoin; and deficiencies of
certain vitamins, such as thiamine and vitamin E.
Some conditions damage the cerebrum as well as the
cerebellum and may cause a combination of cognitive
impairment and incoordination.