896
U N I T 1 0
Nervous System
The most common sensory deficits from spinal nerve
root compression are paresthesias and numbness, par-
ticularly of the leg and foot. Knee and ankle reflexes also
may be diminished or absent.
A herniated disk must be differentiated from other
causes of acute back pain. Diagnostic measures include
history and physical examination. Neurologic assess-
ment includes testing of muscle strength and reflexes.
The straight-leg test is an important diagnostic maneuver.
It is done with the person in the supine position and is
performed by passively raising the person’s leg. The test
can also be done by slowly extending the knee while the
person sits on a table, with both hip and knee flexed at
90 degrees. The maneuver is designed to apply traction
along the nerve root, which exacerbates pain if the nerve
root is acutely inflamed. Normally, it is possible to raise the
leg approximately 90 degrees without causing discomfort
of the hamstring muscles. The test result is positive if pain
is produced when the leg is raised to 60 degrees or less.
Other diagnostic methods include radiographs of the back,
MRI, computed tomography (CT), and CT myelography.
Treatment usually is similar to that for back pain.
Surgical treatment may be indicated when there is
documentation of herniation by an imaging procedure,
consistent pain, or consistent neurologic deficit that
failed to respond to conservative therapy.
Back Pain Emergencies.
Although acute back pain is
usually a non–life-threatening condition, in 5% to 10%
of persons it is a manifestation of a more serious patho-
logic process.
30
Vascular catastrophes (ruptured abdom-
inal aortic aneurysms and dissecting aortic aneurysms),
malignancy, spinal cord compression syndromes, and
infectious processes may all present as acute back pain.
Clinical findings, commonly referred to as
red
flags,
that indicate the possibility of more serious dis-
ease include gradual onset of pain; age younger than
20 years or older than 50 years; thoracic back pain;
history of trauma, fever, chills, night sweats, immu-
nosuppression, or malignancy; unintentional weight
loss; recent procedure known to cause bacteremia; and
history of intravenous drug use.
30
The gradual onset
of pain may be indicative of malignancy or infection.
Back pain that begins before 20 years of age suggests
congenital or developmental disorders, and new-onset
pain in persons 50 years of age or older is more likely
to be a manifestation of serious conditions such as an
aortic aneurysm, malignancy, or compression fracture.
Pain that is aggravated by lying down is a red flag for
malignancy or infection, and pain that improves with
sitting or slight flexion of the spine suggests the pres-
ence of spinal stenosis. Persons with symptoms of large
or rapidly evolving neurologic deficits require urgent
evaluation for possible cauda equina syndrome, epi-
dural abscess, or central disk herniation. Signs and
symptoms that suggest possible cauda equina syndrome
are low back pain associated with bilateral leg weak-
ness (from multiple lumbar nerve root compressions),
saddle area numbness, bowel and bladder incontinence,
or impotence (indicating multiple sacral nerve compres-
sions).
25,30
Reports of neurologic symptoms such as par-
esthesia, motor weakness, and gait abnormalities also
require additional diagnostic tests to rule out spinal
cord compression.
L4
L5
S1
Pain
Nerve root
Numbness
Motor
weakness
Extension of
quadriceps
Dorsiflexion of
great toe
and foot
Plantar flexion
of great toe
and foot
FIGURE 36-10.
Dermatomes of the leg (L1 through S5) where
pain and numbness would be experienced with spinal root
irritation.
SUMMARY CONCEPTS
■■
Muscular dystrophy is a term used to describe
a number of disorders, including Duchenne
muscular dystrophy, that produce progressive
deterioration of the skeletal muscles. Myasthenia
gravis is a disorder of the neuromuscular
junction resulting from a deficiency of functional
acetylcholine receptors, which causes weakness
of the skeletal muscles.
■■
Peripheral nerve disorders, which involve motor
and sensory neurons outside the CNS, include
the mononeuropathies, such as carpal tunnel
syndrome, that involve a single peripheral nerve;
