Clinical Neurology for Psychiatrists, 6th Edition

Central Nervous System Disorders
Lesions in the two components of the central nervous
system (CNS)—the brain and the spinal cord—typically
cause paresis, sensory loss, and visual deficits
(Table 2-1). In addition, lesions in the cerebral hemispheres
(the cerebrum) cause neuropsychologic disorders.
Symptoms and signs of CNS disorders must be
contrasted to those resulting from peripheral nervous
system (PNS) and psychogenic disorders. Neurologists
tend to rely on the physical rather than mental status
evaluation, thereby honoring the belief that ‘‘one
Babinski sign is worth a thousand words.’’
SIGNS OF CEREBRAL HEMISPHERE
LESIONS
Of the various signs of cerebral hemisphere injury, the
most prominent is usually contralateral hemiparesis
(Table 2-2): weakness of the lower face, trunk, arm,
and leg opposite to the side of the lesion. It results
from damage to the corticospinal tract, which is also
called the pyramidal tract (Fig. 2-1). During the corticospinal
tract’s entire path from the cerebral cortex to
the anterior horn cells of the spinal cord, it is considered
the upper motor neuron (UMN) (Fig. 2-2). The
anterior horn cells, which are part of the PNS, are
the beginning of the lower motor neuron (LMN). The
division of the motor system into upper and lower
motor neurons is a basic tenet of clinical neurology.
Cerebral lesions that damage the corticospinal tract
are characterized by signs of UMN injury (Figs. 2-2,
2-3, 2-4, and 2-5):
n Paresis with muscle spasticity
n Hyperactive deep tendon reflexes (DTRs)
n Babinski signs
In contrast, peripheral nerve lesions, including anterior
horn cell or motor neuron diseases, are associated
with signs of LMN injury:
n Paresis with muscle flaccidity and atrophy
n Hypoactive DTRs
n No Babinski signs
Cerebral lesions are not the only cause of hemiparesis.
Because the corticospinal tract has such a long
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course (Fig. 2-1), lesions in the brainstem and spinal
cord as well as the cerebrum may produce hemiparesis
and other signs of UMN damage. Signs pointing to
injury in various regions of the CNS can help identify
the origin of hemiparesis, that is, localize the lesion.
Another indication of a cerebral lesion is loss of certain
sensory modalities over one half of the body, that is,
hemisensory loss (Fig. 2-6). A patient with a cerebral
lesion characteristically loses contralateral position
sensation, two-point discrimination, and the ability to
identify objects by touch (stereognosis). Loss of those
modalities is often called a ‘‘cortical’’ sensory loss.
Pain sensation, a ‘‘primary’’ sense, is initially
received by the thalamus. Because the thalamus is
just above the brainstem, pain perception is retained
with cerebral lesions. For example, patients with
TABLE 2-1 n Signs of Common CNS Lesions
Cerebral hemisphere*
Hemiparesis with hyperactive deep tendon reflexes, spasticity, and
Babinski sign
Hemisensory loss
Homonymous hemianopsia
Partial seizures
Aphasia, hemi-inattention, and dementia
Pseudobulbar palsy
Basal ganglia*
Movement disorders: parkinsonism, athetosis, chorea, and hemiballismus
Brainstem
Cranial nerve palsy with contralateral hemiparesis
Internuclear ophthalmoplegia (MLF syndrome)
Nystagmus
Bulbar palsy
Cerebellum
Tremor on intention ^
Impaired rapid alternating movements (dysdiadochokinesia) ^
Ataxic gait
Scanning speech
Spinal cord
Paraparesis or quadriparesis
Sensory loss up to a ‘‘level’’
Bladder, bowel, and sexual dysfunction
CNS, central nervous system; MLF, medial longitudinal fasciculus.
*Signs contralateral to lesions.
^Signs ipsilateral to lesions.
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