C h a p t e r 3 6
Disorders of Neuromuscular Function
887
Assessment of Motor Function
Disorders of the motor system produce signs and symp-
toms that can be used in localizing the disorder. These
include changes in muscle characteristics (strength,
bulk, and tone), spinal reflex activity, and motor coor-
dination.
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The distinction between LMNs and UMNs is
important because each class of neurons produces dis-
tinctive symptoms.
Muscle Strength, Bulk, andTone
Muscle Strength.
Abnormalities in any part of the
motor pathway can produce impaired strength or mus-
cle weakness.
Paralysis
refers to loss of movement, and
paresis
to weakness or incomplete loss of strength. The
pattern of weakness may be helpful in the localization
of the lesion.
Monoparesis
or
monoplegia
results from
the destruction of pyramidal UMN innervation of one
limb;
hemiparesis
or
hemiplegia,
both limbs on one side;
diparesis
or
diplegia
or
paraparesis
or
paraplegia,
both
upper or lower limbs; and
tetraparesis
or
tetraplegia,
also called
quadriparesis
or
quadriplegia,
all four limbs
(Fig. 36-4).
Paresis or paralysis can be further designated as of
UMN or LMN origin. UMN lesions of the motor cor-
tex or corticospinal tract typically affect the flexors in
the upper extremities more than the extensors, whereas
in the lower extremities, the flexors are more affected.
In LMN or peripheral nerve disorders, the weakness
is predominantly in the distal limb, whereas in muscle
disorders, such as muscular dystrophy, proximal limb
function may be affected sooner than distal limb
function.
Muscle Bulk.
The size of muscle (whether muscles are
normal sized, enlarged, or atrophied) also helps local-
ize the lesion, and sometimes provides helpful hints to
the pathologic process. Muscular atrophy, or loss of
muscle bulk, usually results from LMN lesions as well
as diseases of the muscles themselves. Hypertrophy
refers to an increase in muscle bulk with a propor-
tionate increase in strength. Pseudohypertrophy, as
occurs with Duchenne muscular dystrophy, refers to
an increase in bulk without an accompanying increase
in strength.
Muscle Tone.
Muscle tone is the normal state of
muscle tension. It is assessed by palpating the muscle
while at rest and during passive stretching. With the
person at rest, the joints are put through the normal
range of motion (flexion and extension) by the exam-
iner. Disorders of skeletal muscle tone are characteris-
tic of many nervous system lesions. Any interruption
of the myotatic or stretch reflex circuitry by periph-
eral nerve injury, pathologic process of the neuromus-
cular junction, injury to the spinal cord, or damage to
the corticospinal system can result in disturbances of
muscle tone.
Abnormalities of muscle tone may be described as
hypotonia (less than normal), flaccidity (absent), or
hypertonia, rigidity, spasticity, or tetany (all indicat-
ing higher-than-normal tone). Typically, UMN lesions
produce increased tone, whereas LMN lesions produce
decreased tone. Increased resistance that varies and
commonly becomes worse at the extremes of the range
of motion is called
spasticity.
Resistance that becomes
worse throughout the range and in both directions is
referred to as
lead-pipe rigidity.
Decreased resistance
suggests disease of the LMNs or the acute stages of spi-
nal cord injury. Marked floppiness indicates hypotonic
or flaccid muscles.
Fasciculations.
Fasciculations are visible squirming and
twitching movements of muscle fibers that can be seen as
flickers under the skin.
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They are caused by spontaneous
Monoplegia
Hemiplegia
Tetraplegia or
quadriplegia
Paraplegia
FIGURE 36-4.
Areas of the body affected by monoplegia,
hemiplegia, tetraplegia or quadriplegia, and paraplegia.
The shaded area shows the extent of motor and sensory loss.
(From Hickey JV. The Clinical Practice of Neurological and
Neurosurgical Nursing. 3rd ed. Philadelphia, PA:
J.B. Lippincott; 1997.)
