At the beginning of the 20th century, doctors would treat patients with a widely used form of pain management in which destructive nerve chemicals would promote analgesia. Despite on availability of different approches for destruction of nerves, like Radiofrequency Lesioning, Chemical Neurolytic Block are still very popular in Europe and performed in some clinics in the USA.

The four methods of neurolysis consist of:

1. Cryoablative Techniques

2. Radiofrequency Lesioning

3. Neurosurgical Procedures

4. Chemical Neurolytic Blocks

Chemical Neurolytic Block

A method in which the doctor will promote long-term pain relief by inserting a chemical into the body that will destroy neural structures involved in the perception of pain. The chemicals used for the procedure consist of phenol, ethyl alcohol, hypertonic saline, and other various substances.

Phenol

A chemical compound in which the mixture is made from carbolic acid, phenic acid, phenylic acid, phenyl hydroxide, hydroxybenzene, and oxybenzene. The substance can be prepared to a maximum concentration of 6.7 percent solution in water and is accessible as a sanitary, analytical grade phenol. Using organic solvents such as alcohol and glycerol, this allows the substance to be highly soluble. One way to increase the concentration to 15 percent is to add minuscule quantities of glycerol or water-soluble radio-opaque contrast material.  One way we establish control over the circulation and allow the substance to target the exact area needed to be destroyed is by mixing it with glycerol. A stronger form of this method and allows for widespread nerve destruction is when mixing it with water instead of glycerol. Understanding which diluent to use depends on how much neurolysis is needed. 

If phenol is protected from light and kept cool in a refrigeration unit, the substance’s shelf life is one year. Once phenol is exposed to sunlight and oxygen the substance turns red due to oxidation. The metabolic process happens in the liver by conjugation to glucuronides and oxidation to equinol compounds or to carbon dioxide and water. Excretion of metabolites occurs in the kidneys. Phenols side effects include central nervous system stimulation, cardiovascular depression, nausea, and vomiting. Serious side effects are generally less likely to occur if the organized dose is less than 100mg, although if the organized doses exceed 5 grams, convulsive seizures and central nervous system depression can occur.

The first phases of its use as a neurolytic agent came about it 1935 by Putnam and Hampton

In 1936, Putnam and Hampton began its first phases as a neurolytic agent. The process of using phenol to destroy nerves works by inducing protein precipitation. The in-depth process works by losing cellular fatty elements and creates a separation of the myelin sheath from the axon, and axonal edema.  To refrain from losing motor function, a concentration of 2-3 percent saline must be added to the phenol solution. Comparing the efficacy of 3 percent phenol in saline to 40 percent alcohol can be understood through the fact that it has immediate local anesthetic effects because of its immediate selective impact on smaller nerve fibers. The differential blocking ability is assumed to act as the result of small vessel destruction that initially spares large fibers. Although, the ability to evaluate the blocking effects cannot be done until the local anesthetic effect, dissipates, which can take up to anywhere from 24 to 48 hours. The neurolytic impact can only be observed efficiently after a 2 to 7-day period. If incomplete neurolysis is done and the patient is experiencing poor pain relief after a two-week period, they must come back in to repeat the procedure.

After the injection of phenol, although not impossible, the succeeding fibrosis causes nerve regeneration to become difficult. The reconstruction of nerves will occur at a gradual pace of 1 to 3 mm per day if the nerve cell body is intact. Ways to inject phenol can be inthrathecally and epidurally. Compared to the CSF, phenol in glycerol is hyperbaric. Other uses for it include peripheral nerve blocks, paravertebral somatic blocks, and sympathetic blocks.

Indications for Chronic Neurolysis

1. Control of chronic, unmanageable, non-terminal pain that has been deemed unresponsive to other methods of pain relief.

2. Methods of treatment for pain from cancer in patients who have less than a year to live

3. Other forms of treatment for those who suffer from spasticity, to enhance balance, gait, self-care, and over-all rehabilitation. Unlike those treated for pain relief through neurolytic blocks, motor or mixed nerves are attacked preferentially in the management of spastic disorders.

Patient Selection for Chemical Neurolysis

Patients must undergo a complete evaluation before being deemed ready for the procedure. It must be noted that the patient's pain does not respond to other methods of treatment. The doctors Leovigildo Reyes, MD, Lawrence Eppelbaum, MD and Hamid Tehrani, MD at Back Pain Relief Service and Consulting Inc. in Atlanta, Georgia will locate the exact spot of your pain for there not to be a need for multiple segmental blocks. The doctors will thoroughly explain the risks as well as create a strong sense of communication between the patient and doctor, before moving forward with the procedure.

Chemical neurolysis should also be used in union with other forms of therapy including, pharmacotherapy, psychologic, counseling, and physical therapy. Multiple diagnostic local anesthetic blocks should be done to create an accurate prediction for a successful outcome of neurolysis.  The period and length of analgesia should match with the type of agent used. For the patient to experience the effects of the neurolytic block with the least amount of side effects, a local anesthetic block should be used to find the anatomic nature of the pain. 

Depending on the skill of the physician and the type of block administered, the success and duration of it can differ anywhere from minimal to maximum pain relief that lasts from weeks to months.