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Chemical Neurolysis

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What is "spasticity?" What is
"motor tone" and what makes it abnormal?

Damage to the brain or spinal cord
sometimes causes unusual postures, stiffness or, at worst,
rigidity. People exposed to neurological rehabilitation
settings frequently hear the term "tone" in
description of the state of an arm or a leg. "Tone"
refers to the resting state of relaxation or tension in a
group of muscles. After significant brain or spinal cord damage (for example by traumatic injury, stroke, hemorrhage or
multiple sclerosis) there may be a marked increase in tone in
one or more muscles groups. If this problem persists for
weeks to months, ligaments, tendons and muscles in the
affected limb may shorten or form "contracture."
Contracture can, in turn, make the level of disability worse
than it would otherwise be by imposing mechanical limitations
upon movement in a limb that is weakened by brain or spinal
cord damage.

What are "Nerve Blocks?"

A nerve block is the injection of either a
local anesthetic (when a test block is being done) or an
alcohol (for long-lasting effect) into a peripheral nerve or
its branches. The idea in both cases is to decrease the
amount of nerve activity to and from spastic or rigid
muscles. Nerve blocks have been used for over 30 years to
treat spasticity and rigidity complicating neurological
disorder.

A Marcaine (Bupivacaine) Block
involves the injection of a long-acting local anesthetic
into/near a nerve or branch of a nerve. The effect of such an
injection usually lasts for hours. This kind of injection is
used to assess the effect of a nerve block on the muscle(s)
suspected of exerting the major influence upon a particular
problem when it is unclear whether a more permanent block
would solve the problem of interest. The Marcaine effect is
always temporary but generally lasts long enough to allow
assessment of the functional impact to be expected with a
longer lasting phenol block.

A Phenol Block involves injection
of a dilute alcohol (5% aqueous phenol) into a nerve or nerve
branch. Phenol destroys many of the nerve fibers that it
comes in contact with, in effect ‘thinning’ out the nerve
overall. The relief of tone experienced with a phenol block
typically lasts months, but in some cases can last years. The
reason for the limited effect is that, unlike brain or spinal
cord cells, peripheral nerves (going from the spinal cord out
to muscles) are often able to regenerate. When they do, the
effects of a phenol block may wear off.

When is it appropriate to consider using a Nerve
Block to treat spasticity/rigidity?

Several points need to be considered
before a nerve block is suggested or performed. First, the
problem with hypertonia/spasticity should be fairly
long-standing (months) and not the sort of problem for which
an antispasticity medication might be satisfactory.
Antispasticity medication often has a side-effect profile
which makes it an undesirable option in an individual case.
Also, if a tone-related problem is chiefly a very local one
(for example, right-sided ankle clonus/shaking interfering
with transfers or walking), it may be easier to achieve the
desired effect with a nerve block than with a medication with
no systemic side-effects to worry about.

There needs to be a clear reason for doing
a block. Spasticity or ‘tightness’ in a limb alone is not
reason for doing a block. If hygiene is being threatened (as
in the case of spasticity which threatens access to armpits
or hands for washing), a nerve block may be indicated.
Another situation in which blocks often help a lot are when
deforming contracture appears to be an evolving consequence
of prolonged hypertonia (for example, a hand in which fingers
are curling despite daily repeated stretching). Sometimes,
spasticity can actually ‘mask’ function. That is, there can
be so much tightness in a limb that weak voluntary movements
are very slow or very small. But, when tone is drastically
reduced after a nerve block, voluntary control may be
improved. There should always be a concrete objective for
performing a nerve block. This objective should not be one
that could be accomplished in some safer, less-invasive way.
The goal should relate to hygiene, contracture-prevention or
meaningful increase in function.

Are there any risks or complications to nerve
blocks?

As with any medical procedure, there may
be undesired effects or complications arising from a nerve
block.

Allergic response to Marcaine is possible
but should not occur in people who have had dental anesthesia
(injections) in the past. Any history of allergy to local
anesthetics should be brought to the attention of the
physician who is going to be performing a block. Allergy to
phenol is extremely rare.

Infection at the site of injection is
possible, but especially unlikely with phenol which is
bacteriocidal in the concentration used. Accidental puncture
of an artery or vein is possible, but minimized by good
technique.

Occasionally, performance of a nerve block
results in development of pain in areas of skin served by the
nerve that was injected. This problem is more likely when the
nerve being injected carries both sensory and motor
information (for example, the median nerve at the elbow). The
pain tends to occur in the part of the limb served by that
nerve and may last for weeks, though often it is shorter
lived. If it lasts longer than four weeks, a repeat block may
abolish the pain.

As might be expected, weakness in muscles
supplied by the target nerve may follow a block, but
significant weakness after a block is unusual.

If the nerve block is being performed in
the axillary (arm-pit) area, there is a theoretical risk of
puncture of the lung cavity. Though the author is unaware of
this complication ever being reported, it is of special
significance in that it could become a life-threatening
issue–especially if the opposite lung is compromised by
disease or injury.

Another special circumstance involves
phenol blocks done in the area of nerve roots near the spinal
column (i.e.-lumbosacral or paravertebral blocks). If phenol
is accidentally injected into the space containing spinal
fluid, it might then affect nerves that control portions of
bowel, bladder and sexual function. Special precautions are
taken to avoid such a complication when this type of block is
performed.