Chapter 72 Central and Peripheral Neurolysis

Question 1

Glycerol

Answer 1

used for the treatment of trigeminal neuralgia.

Question 2

Phenol and ethyl alcohol

Answer 2

the only two agents commonly used in the epidural or intrathecal
space, as well as for sympathetic plexus neurolysis.

Question 3

Chemical and surgical neurolysis is primarily limited to

Answer 3

patients with pain associated with terminal malignancies. These procedures provide the most benefit in the oncology patients in whom more conservative measures were unsuccessful, possessed too high a side effect burden, or
unable to be performed

Question 4

In patients in extremis, neurolysis represents a

Answer 4

palliative measure to provide pain relief while
maintaining the patient’s ability to interact with family and friends in their final days to months of life. This can be
preferable to systemically delivered opioids, which may
interfere with the patient’s mental status enough to diminish
meaningful communication with family and friends.

Question 5

Neurolysis is an alternative to allow patients the ability to

Answer 5

control their pain with less systemic medication,

significantly improving their quality of life.

Question 6

Intrathecal Neurolysis: Indications for Neurolytic

Spinal Blockade

Answer 6

Intractable cancer pain (advanced or terminal malignancy)
Failure of medical and interventional analgesic therapy
Intolerable side effects of current therapy
Unilateral pain
Pain restricted to one to four dermatomal levels
Pain located in the trunk, thorax, abdomen
Primary somatic pain mechanism
Absence of intraspinal tumor spread
Effective analgesia with local anesthetic block
Informed consent of patient

Question 7

Although neurolysis can provide analgesia in the dermatomal distribution affected by the block, it will not necessarily
provide pain relief from

Answer 7

an expanding tumor or new metastasis. In addition, the effects of this therapy can be temporary, and will diminish over time, requiring re- administration
of the neurolytic agent

Question 8

Adverse Effects of Neurolysis

Answer 8

limb weakness and loss of bowel or bladder tone

Question 9

With neurolysis patients

with complaints of neuropathic pain will not get the desired results compared to those with

Answer 9

visceral or somatic pain

Question 10

Due to the nature of neurolytic administration, it is ideal

for controlling

Answer 10

unilateral pain in the trunk and focused
to a few adjacent dermatomes. However, in the presence of an intraspinal tumor, the effectiveness of these techniques will decrease, making these patients unsuitable
candidates. Neuraxial neurolytic therapy is ideal for patients
with advanced or terminal malignancy and unilateral somatic
pain

Question 11

PATIENT PREPARATION

Answer 11

Once a definitive plan is established, informed
consent should be explained in detail to the patient, outlining
all the risks associated with the particular procedure. A thorough neurologic examination before any invasive
techniques are attempted is vital not only for assessing the
effectiveness, but it can provide a baseline assessment in
the event of any potential complications.

Question 12

Before any neurolytic agents are used, it is advisable to perform a
diagnostic blockade with

Answer 12

a local anesthetic that reproduces the planned intervention. This diagnostic maneuver helps to confirm needle placement and can provide information
about the level of effectiveness of the neurolysis.

Question 13

The choice of neurolytic

agent is based on

Answer 13

the location of needle placement, the ability of the patient to get in the required position, and the volume of injectate required

Question 14

Baricity

Answer 14

may play a role in determining which neurolytic agent to use

for the patient.

Question 15

Phenol vs. Ethanol

Answer 15

Phenol is a hyperbaric agent that would be

more appropriate for pelvic and saddle blocks compared with a hypobaric agent such as ethanol.

Question 16

Ethyl alcohol injections perineurally are associated with

Answer 16

burning dysesthesias running along the course of the nerve. To alleviate this known effect, most practitioners inject a local
anesthetic preceding the use of ethyl alcohol.

Question 17

The neurolytic action of alcohol is produced by

Answer 17

the extraction of
neural cholesterol, phospholipids, and cerebrosides, and the precipitation of mucopeptides. These actions result in sclerosis of the nerve fibers and myelin sheath, leading to demyelination

Question 18

During neurolytic action of alcohol the basal lamina of the Schwann cell sheath remains intact, allowing for

Answer 18

new Schwann cell growth, thereby providing the framework for subsequent
nerve fiber growth. This framework encourages the regeneration of axons, but only if the cell bodies of these nerves are not completely destroyed.

Question 19

Areas of demyelination can be seen in

Answer 19

posterior columns, Lissauer’s tract, and the dorsal root,

followed by Wallerian degeneration to the dorsal horn.

Question 20

Intrathecal alcohol injection results in

Answer 20

rapid uptake of alcohol and variable injury to the surface of the spinal cord. Ethyl alcohol is quickly absorbed from the cerebrospinal fluid (CSF) so that only 10% of the initial dose
remains in the CSF after 10 min and only 4% after 30 min.

Question 21

The rapid spread from the injection site of Intrathecal alcohol means

Answer 21

larger volumes are required than for phenol, which in

turn may result in local tissue damage

Question 22

The use of ethanol as a neurolytic agent has been associated with

Answer 22

a disulfiram-like effect, known as acetaldehyde syndrome. The patients experienced flushing, hypotension,
tachycardia, and diaphoresis within 15 min of alcohol administration.

Question 23

medications that may cause disulfiram-like effects after

peripheral neurolytic blocks with alcohol, such as

Answer 23

chloramphenicol,
beta-lactams, metronidazole, tolbutamide,
chlorpropamide, and disulfiram.

Question 24

specific gravity of Ethyl alcohol and CSF

Answer 24

Ethyl alcohol has a
specific gravity of less than 0.8, and CSF has a specific
gravity of slightly greater than 1.0. Within the CSF, alcohol
is hypobaric and will move against gravity, “floating”
upward. Therefore, positioning of the patient is an
extremely important factor to consider when planning
the procedure.

Question 25

The administration of ethanol for the purpose of neurolysis can have catastrophic consequences. It has been associated with

Answer 25

both transient and permanent paraplegia in both celiac plexus and intrathecal blocks. It has been postulated that these effects are secondary to vasospasm of the spinal arteries by the direct action of alcohol.

Question 26

Characteristics of Neurolytic Agents: Alcohol

Answer 26

``` Physical properties: Low water solubility Stability at room temperature: Unstable Concentration: 100% Diluent: None Relative to cerebral spinal fluid: Hypobaric Patient position: Lateral Added tilt: Semiprone Painful side: Uppermost Injection sensation: Burning pain Onset of neurolysis: Immediate Cerebrospinal fluid uptake ends: 30 min Full effect: 3-5 days ```

Question 27

Characteristics of Neurolytic Agents: Phenol

Answer 27

Physical properties: Absorbs water on air exposure Stability at room temperature: stable Concentration: 4-7%. 4%-10% are typically used for neurolysis Diluent: Glycerin Relative to cerebral spinal fluid: Hyperbaric Patient position: Lateral Added tilt: Semisupine Painful side: Most dependent Injection sensation: Painless, warm feeling Onset of neurolysis: Delayed (15 min) Cerebrospinal fluid uptake ends: 15mins Full effect: 1 day

Question 28

INTRATHECAL ALCOHOL A neurolytic intrathecal block should be performed at the level where

Answer 28

the target dorsal root leaves the spinal cord, and not at the level where it passes through the intervertebral foramen. The latter is not recommended due to mismatch of the spinal cord level and vertebral bone level (especially as one progresses from high thoracic levels to low lumbar).

Question 29

INTRATHECAL ALCOHOL An accurate determination of the level to be blocked should be evaluated according to

Answer 29

dermatome and sclerotome charts, as well as selective local anesthetic blockade

Question 30

INTRATHECAL ALCOHOL the patient should be positioned laterally so that the

Answer 30

rootlets (dorsal root entry zone [DREZ]) are above the injection site. This positioning is necessary given that alcohol will float in the CSF due to its greater specific gravity that renders it hypobaric

Question 31

INTRATHECAL ALCOHOL The patient should also be turned 45 degrees toward the prone position. This will

Answer 31

raise the DREZ (dorsal root entry zone) horizontally so it will be superior to the ventral nerve rootlets.

Question 32

INTRATHECAL ALCOHOL Technique

Answer 32

After proper patient positioning, correct needle depth must be obtained. A short, beveled needle is placed slowly into the predetermined location until arriving at the epidural space. This is best-confirmed using loss of resistance to air. After ascertaining that the epidural space has been reached, the needle should be advanced slowly while aspirating continuously until it reaches the intrathecal space. Once the needle is in the intrathecal space, adjust the bevel so it is anterior to the arachnoid mater. placement may be verified with radiographic imaging and contrast dye administration. The practitioner may then inject the alcohol, or it may be preceded by a low-volume injection of local anesthetic.

Question 33

INTRATHECAL ALCOHOL Drug and Dose

Answer 33

Using a tuberculin syringe, the alcohol is injected in 0.1-ml increments, with at least 60 seconds (preferably 90 sec) between repeat administrations. Total alcohol volume should not exceed 0.5 to 0.7 ml.

Question 34

INTRATHECAL ALCOHOL After injection, the patient should remain

Answer 34

in the same position for 15 to 30 min. This immobilization allows the alcohol to exert its maximal effect at the desired location, with minimal spread to adjacent levels. After the 30-min time period, a neurologic examination should be performed.

Question 35

INTRATHECAL ALCOHOL Three to 5 days after the alcohol injection, the patient’s pain should be evaluated to assess

Answer 35

effectiveness of the technique and determine whether repeat injections are required.

Question 36

Phenol

Answer 36

a benzene ring with one hydroxyl group substituted | for a hydrogen atom.

Question 37

Phenol in water and at room temperature

Answer 37

Phenol is poorly soluble in water and, at room temperature, forms only a 6.7% aqueous solution. Consequently, phenol is frequently prepared with contrast dyes and either sterile water, saline or glycerin

Question 38

When phenol is exposed to | room air, it undergoes

Answer 38

oxidation and turns a reddish color; however, it has a shelf life of approximately 1 year if refrigerated and shielded from light exposure.

Question 39

When phenol is prepared with glycerin

Answer 39

it has limited spread, | and, hence, injections are well localized.

Question 40

Unlike alcohol, phenol injection

Answer 40

has an initial local anesthetic effect. It is not associated with localized burning, but instead, creates a sensation of warmth and numbness.

Question 41

Preparations of phenol in glycerin

Answer 41

When phenol is prepared in glycerin, it has a specific gravity of 1.25, making it hyperbaric. Preparations of phenol in glycerin are highly viscous, which may make administration through a spinal needle difficult. Warming the injectate in a warm water bath before drawing it up into a tuberculin syringe may facilitate the ease of injection.

Question 42

In using Phenol Careful patient positioning

Answer 42

to allow phenol to settle into the desired location is important, and contrary to the concepts associated with patient positioning for alcohol neurolysis.

Question 43

Dilute and concentrated intrathecal phenol

Answer 43

Dilute intrathecal phenol can producea transient local anesthetic blockade, while increased concentrations can produce significant neural damage.

Question 44

Phenol concentrations have a direct relationship with | the extent of neural damage

Answer 44

At concentrations less than 5%, phenol instigates protein denaturation of axons and surrounding blood vessels. At concentrations greater than 5%, phenol can produce protein coagulation and nonselective. segmental demyelination.

Question 45

When compared to alcohol, phenol seems to facilitate

Answer 45

axonal regeneration in a shorter period of time.

Question 46

Systemic doses of phenol in excess of 8.5 g are associated with toxic side effects.

Answer 46

These effects initially are convulsions, followed by CNS depression, and, finally, cardiovascular collapse. Chronic long-term exposure may be associated with renal toxicity, skin lesions, and gastrointestinal effects. However, phenol is not classically used in long-term settings, and the customary doses of less than 100 mg are unlikely to produce any systemic effects

Question 47

INTRATHECAL PHENOL The pain location should be determined with

Answer 47

dermatome and sclerotome mapping, and preferably | isolated with a diagnostic injection of local anesthetic or contrast dye under fluoroscopy.

Question 48

INTRATHECAL PHENOL When using phenol, the patient’s targeted anatomy must be

Answer 48

facing down, the patient leaned 45 degrees supine, and the spinal needle diameter must be larger due to the increased viscosity. The “sinking” of phenol into its area of effect requires the targeted rootlets to be under the site of administration

Question 49

The feeling of warmth from the phenol is fleeting, and may provide some pain relief, but neurolysis is slower to manifest than with alcohol

Answer 49

The phenol can take 15 min before it starts to exert its effect. Although there is less outward diffusion with phenol compared to alcohol, the patient should be maintained in position for 30 min after phenol administration. The full effect of phenol manifests over approximately 24 hrs

Question 50

A short, 20-gauge needle should allow the thick phenol solution to be injected in most situations. However, if this proves difficult

Answer 50

warming the injectate in a warm water bath before drawing may ease the flow of the injection.

Question 51

INTRATHECAL PHENOL Drug and Dose

Answer 51

Like alcohol, phenol is injected in 0.1-ml increments, with 60 to 90 s between subsequent injections. Phenol is injected up to a total dose of 0.5 to 0.7 ml.

Question 52

An epidural neurolytic block provides

Answer 52

bilateral pain relief;

Question 53

Epidural neurolysis is used for

Answer 53

abdominal cancer pain of both visceral and mixed somatic | and visceral origin

Question 54

Epidural neurolysis remains popular, not only due to its

Answer 54

increased safety index and the ease for repeated injections, but also for its greater efficacy on thoracic and cervico-thoracic junction pain.

Question 55

EPIDURAL NEUROLYTIC BLOCK Selecting the appropriate size needle depends on the agent used

Answer 55

The use of phenol in glycerin requires a large-bore needle, while the use of aqueous phenol, phenol in saline, or alcohol permits the use of a much smaller needle, in which case an epidural needle or catheter may be used.

Question 56

EPIDURAL NEUROLYTIC BLOCK The catheter

Answer 56

a soft, nonkinking, styletted version that can be maneuvered with precision, and allows confirmation of position with the injection of a small amount of local anesthetic.

Question 57

EPIDURAL NEUROLYTIC BLOCK Unlike the intrathecal administration of neurolytic agents, needle or catheter tip location should be chosen

Answer 57

near the vertebral levels that correspond to the dermatomal levels manifesting in the patient’s pain area in order to deposit the medication over the appropriate nerve roots.

Question 58

EPIDURAL NEUROLYTIC BLOCK Once needle and patient positioning have been established, what is performed to confirm proper needle depth and location.

Answer 58

the use of contrast-enhanced fluoroscopic imaging and a local anesthetic test dose

Question 59

EPIDURAL NEUROLYTIC BLOCK Dosing

Answer 59

Doses ranging from 2 to 5 ml are usually adequate, | with doses increasing as location moves more caudally

Question 60

COMPLICATIONS ASSOCIATED WITH INTRATHECAL AND EPIDURAL NEUROLYSIS

Answer 60

incomplete block to limb weakness or bladder/rectal paresis the most common complication is failure of the procedure to provide significant pain relief.

Question 61

Poor pain relief can have numerous etiologies.

Answer 61

patients to have high expectations for pain relief and have those expectations not met by neurolysis. Another cause of inadequate pain relief may be as simple as an incomplete block that can be remedied with a repeat dose. there is always the possibility that the block works well, but that local spread of the neurolytic agent may have produced peripheral damage

Question 62

There are complications due to entry into the anatomic space where these medications are administered. They include

Answer 62

postdural puncture headaches, meningitis, arachnoiditis, and | neural damage due to trauma. Postdural headaches usually resolve quickly, within 1 to 5 days.

Question 63

Complications related to neurolytic agents include

Answer 63

loss of motor function due to neurolysis of the ventral rootlets, loss of touch and proprioception, and loss of sphincter tone. Of these potential complications, loss of bowel or bladder sphincter tone is relatively common. The complications caused by the neurolytic agents are usually transient.

Question 64

Complications can be specific to location along the spine where the neurolysis is performed.

Answer 64

At the cervical level, damage can occur to the brachial plexus, most often manifesting as limb paresthesias. Complications at the thoracic level are the least common relative to the cervical and lumbar level. Below the L1 spinal level, injections may travel into the cauda equina, where anterior and posterior roots are not separated. This factor that may make the degree of motor or sensory effect difficult to predict.

Question 65

Peripheral neurolytic | blocks are frequently associated with

Answer 65

neuritis and deafferentation | pain, in addition to postinjection dysesthesias

Question 66

Neurolytic intercostal blocks may help with pain that | originates from

Answer 66

the thoracic wall, abdominal wall, or parietal perineum.

Question 67

Intercostal blocks are performed by

Answer 67

“walking the needle off” the inferior border of the rib. Proper needle placement should be verified using fluoroscopy and paresthesias. Typically, phenol is the agent of choice. Phenol is injected in 1- to 2-ml doses of 5% phenol.