C h a p t e r 3 6
Disorders of Neuromuscular Function
893
The successful regeneration of a nerve fiber in the PNS
depends on many factors. If a nerve fiber is destroyed
relatively close to the neuronal cell body, the chances
are that the nerve cell will die; if it does, it will not be
replaced. If a crushing type of injury has occurred, par-
tial or often full recovery of function occurs. Cutting-
type trauma to a nerve is an entirely different matter.
Connective scar tissue forms rapidly at the wound site,
and when it does, only the most rapidly regenerating
axonal branches are able to get through to the intact
distal endoneurial tubes. A number of scar-inhibiting
agents have been used in an effort to reduce this hazard,
but have met with only moderate success. In another
attempt to improve nerve regeneration, various types of
tubular implants have been used to fill longer gaps in the
endoneurial tube.
Mononeuropathies
Mononeuropathies usually are caused by localized con-
ditions such as trauma, compression, or infections that
affect a single spinal nerve, plexus, or peripheral nerve
trunk. Fractured bones may lacerate or compress nerves,
excessively tight tourniquets may injure nerves directly
or produce ischemic injury, and infections such as her-
pes zoster may affect a single segmental afferent nerve.
Recovery of nerve function usually is complete after
compression lesions and incomplete or faulty after nerve
transection.
CarpalTunnel Syndrome.
Carpal tunnel syndrome is a
relatively common entrapment mononeuropathy, caused
by compression of the median nerve as it travels with
the flexor tendons through a canal made by the carpal
bones and transverse carpal ligament
18–20
(Fig. 36-8).
It can be caused by a variety of conditions that produce a
reduction in the capacity of the carpal tunnel (i.e., bony
or ligamentous changes) or an increase in the volume of
the tunnel contents (i.e., inflammation of the tendons,
synovial swelling, or tumors). Carpal tunnel syndrome
may be a feature of a number of systemic diseases, such
as rheumatoid arthritis, hyperthyroidism, acromegaly,
and diabetes mellitus. Most cases, however, are due to
repetitive use of the wrist (i.e., flexion–extension move-
ments and stress associated with pinching and gripping
motions).
Carpal tunnel syndrome is characterized by pain, par-
esthesia (tingling), and numbness of the thumb and first,
second, third, and half of the fourth digits of the hand;
pain in the wrist and hand, which worsens at night;
atrophy of the abductor pollicis muscle; and weakness
in precision grip. All of these abnormalities may con-
tribute to clumsiness of fine motor activity.
Diagnosis usually is based on sensory disturbances
confined to median nerve distribution and a positive
Tinel or Phalen sign.
18,20
The
Tinel sign
is the develop-
ment of a tingling sensation radiating into the palm of
the hand that is elicited by light percussion over the
median nerve at the wrist. The
Phalen maneuver
is per-
formed by having the person hold the wrist in complete
flexion for approximately a minute; if numbness and
paresthesia along the median nerve are reproduced or
exaggerated, the test result is considered to be positive.
Electromyography and nerve conduction studies often
are done to confirm the diagnosis and exclude other
causes of the disorder.
Treatment includes a variety of options includ-
ing nonsteroidal anti-inflammatory agents, injection
of corticosteroids, immobilization of the wrist with
splints, rehabilitation modalities (e.g., ultrasound,
stretching, and strengthening exercises), and surgery.
Measures to decrease the causative repetitive move-
ments should be initiated. Splints may be confined
to nighttime use. When splinting is ineffective, cor-
ticosteroids may be injected into the carpal tunnel to
reduce inflammation and swelling. Surgical interven-
tion consists of operative division of the volar car-
pal ligaments as a means of relieving pressure on the
median nerve.
Polyneuropathies
Polyneuropathies involve demyelination or axonal
degeneration of multiple peripheral nerves that leads to
symmetric sensory, motor, or mixed sensorimotor defi-
cits. Typically, the longest axons are involved first, with
symptoms beginning in the distal part of the extremi-
ties. If the autonomic nervous system is involved, there
may be postural hypotension, constipation, and impo-
tence. Polyneuropathies can result from immune mecha-
nisms (e.g., Guillain-Barré syndrome), toxic agents (e.g.,
arsenic polyneuropathy, lead polyneuropathy, alcoholic
Median
nerve
Transverse
carpal
ligament
FIGURE 36-8.
Carpal tunnel syndrome: compression of the
median nerve by the transverse carpal ligament. (Courtesy of
Carole Russell Hilmer, C.M.I.)
