Overview of Phenol Nerve Block
Neurolysis is a process that temporarily blocks the function of a particular nerve or group of nerves. This can be achieved by injecting certain chemicals, using extreme cold (a technique called cryotherapy), or with a procedure known as radiofrequency ablation. The purpose of neurolysis is often to manage pain. The first recorded use of this method was in 1863, when a doctor named Luton used irritating chemicals to relieve pain in certain parts of the body. This seemed to be particularly effective for people suffering from extreme leg pain due to a condition known as sciatic neuralgia.
Decades later, in 1926, other doctors started using a chemical called phenol to carry out neurolysis. By 1955, this chemical was injected into the space around the spinal cord (known as an intrathecal injection). Furthermore, studies published in 1959 reported that phenol injections could successfully treat muscle stiffness.
Phenol is a complex chemical compound that includes components like carbolic acid, phenic acid, and oxybenzone. When injected near nerves, phenol breaks down proteins, leading to changes in the nerve cells and their protective covering, referred to as the myelin sheath. As a result, nerves cease to function normally, which contributes to the loss of pain sensation. Phenol’s impact might be due to a combination of nerve damage and reduced blood supply (ischemia). Upon examination under a microscope, it’s evident that phenol injections can lead to nerve damage, muscle loss, and tissue death (necrosis).
Nowadays, neurolysis is typically carried out using phenol or ethanol, but other substances like salt solutions, glycerol, and chlorocresol also have been used in the past.
Anatomy and Physiology of Phenol Nerve Block
The specific details of the body’s structure can vary depending on the type of procedure being done. For example, a type of treatment called phenol neurolysis can be performed on different nerves throughout your body. This procedure uses a chemical, phenol, to temporarily or permanently stop nerves from sending pain signals. However, this isn’t commonly done with the nerves located in your spine, which is known as neuraxial drug administration.
When the doctor is doing the procedure, they have to be very careful to make sure the needle goes to the exact nerve that needs to be treated. They use technologies like ultrasound, x-rays (fluoroscopy), or tools that can stimulate your nerves to precisely identify the right spot.
Why do People Need Phenol Nerve Block
Phenol neurolytic injections, a type of medical procedure, can be used to manage constant and extreme pain when other treatments have been unable to provide relief. This procedure involves injecting a medicine called phenol to temporarily damage specific nerves and block pain signals. However, it’s essential to choose patients wisely for this treatment. Before considering this procedure, it should be clarified that a patient has tried other types of pain control methods.
Just as importantly, a patient’s mental health status needs to be evaluated before deciding to move forward with this treatment. Given the potential side effects of neurolytic injections, it’s pivotal for doctors and patients to have a full discussion about the pros, cons, and alternatives to this procedure beforehand. Even when other therapies have not worked, phenol injections should be used as a part of a larger treatment plan, which might include medication, counseling, and physiotherapy.
To ensure the likely success of neurolytic injections, a ‘trial run’ is carried out using a local anesthetic block (a numbing medicine) on the targeted nerve. This helps confirm the physical source of the pain and gives the patient an idea of what the effects of the actual neurolytic block will feel like, without experiencing the potential side effects. If this trial injection results in short-term pain relief, the patient might experience the same benefit from the neurolytic injection.
Phenol injections can be used on various parts of the nervous system, such as peripheral nerves (nerves outside your brain and spinal cord), a group of nerves called the celiac plexus, and other areas depending upon the requirement. Apart from managing stubborn, chronic pain, it can be used to treat severe muscle stiffness, improve body balance, walking, and self-care abilities, and manage pain in cancer patients with a limited life expectancy. Specifically, phenol is often used to decrease severe muscle tone or stiffness. It can be injected into the spinal fluid to treat muscle stiffness caused by spinal cord diseases and severe pain conditions like terminal abdominal or pelvic cancers. Additionally, it can be administered to decrease excess sympathetic nerves activity in peripheral vascular disease (a condition that causes narrowed or blocked blood vessels outside the heart).
One key point to keep in mind is that the procedure is slightly different when aiming to reduce pain versus treating muscle stiffness. For instance, motor nerves (those controlling muscle movements) or mixed nerves (those carrying both sensory and motor fibers) are especially targeted when treating muscle stiffness disorders.
When a Person Should Avoid Phenol Nerve Block
There are a few situations where certain procedures cannot be carried out on a patient for their own safety. Here are some examples:
If a patient has chosen not to have a procedure done, it obviously can’t be done. This is what doctors mean when they mention “patient refusal”.
Active infection is another issue. This is when the patient has a current ongoing illness, like a flu or a cold. It’s generally not safe to carry out procedures on someone who has an active infection.
If a patient has a tumor at the point where the doctor would need to insert a needle (for conditions that don’t involve cancer or muscle tightness), it’s also not safe to carry out the procedure. The risk of spreading the disease or causing complications is too high.
Bleeding disorders or use of blood thinning medication can also prevent a procedure from taking place, especially if the injection needs to take place in an area where it could be risky, such as near the spinal cord (the neuraxis). These conditions make it hard for the body to stop bleeding, so they can make procedures more dangerous.
Equipment used for Phenol Nerve Block
When your doctor needs to numb a specific area of your skin, they typically use a small, thin needle, often a 25-gauge needle, to inject a local anesthetic. This is a type of drug that blocks pain signals in that area. Finding the exact location to inject the anesthetic might involve the use of certain tools — such as fluoroscopy, which provides real-time moving images of the inside of your body, ultrasound, which uses sound waves to create images of structures in your body, or nerve stimulators, devices that send small electrical signals to nerves.
If your doctor is planning to use a neuraxial approach, meaning they’ll be targeting nerves along your spine, the size or type of needle they use will depend on several different factors. These could include your body size and shape, your age, the doctor’s preference, and other considerations that might affect the procedure.
If the doctor will be performing a peripheral nerve neurolysis, a procedure used to block pain signals from a specific nerve in your body outside of your spine, the choice of needle length and size will also depend on the location and depth of the target nerve, the doctor’s preference, use of a peripheral nerve stimulator, and other factors.
Preparing for Phenol Nerve Block
Phenol, used in hospitals, is a very sensitive chemical. It comes as an 89% solution and must be prepared by the hospital pharmacist. It doesn’t stay stable at room temperature and can react with air and light, turning red. Depending on what the medical team wants it to do, phenol can be prepared in a water-based, glycerin, or fat-based solution and then diluted to the desired strength, usually between 2% to 3%.
When phenol is mixed with glycerin, it moves slowly resulting in a very limited spread kept at the injection site. This version of phenol, when diluted with glycerin, is heavier in comparison to cerebrospinal fluid – the fluid found in your brain and spine. Water-based phenol solutions are stronger, have a wider spread, and a dye may be added to help doctors see it during a type of X-ray called fluoroscopy.
We haven’t figured out the best concentration of phenol to use for nerve damage treatment because it hasn’t been thoroughly researched, but some studies suggest the ideal range might be between 3% to 12%. Using less than 5% can cause damage to nerve fibers and blood vessels, while using more than 5% can cause protein to clump together and potentially damage the tiny fatty structures covering nerve fibers. Doctors must be careful not to give more than 1 gram in a day, especially in patients with severe liver disease since phenol is broken down by the liver.
Before starting the procedure, the performing healthcare provider needs to explain the procedure to you and get your consent. How you’ll be positioned during the procedure depends on which nerve they are targeting. Usually, little to no sedation is required, as the phenol injection is painless because of it has instant numbing qualities. This is unlike alcohol, which can be very painful when injected. Doctors must follow a very clean method to prevent infection.
How is Phenol Nerve Block performed
Sometimes, doctors use a medical procedure to target a specific nerve in your body to treat health issues. During this procedure, the doctor will use different tools like an ultrasound, a device that creates pictures of the inside of your body using sound waves, or a nerve stimulator, something that creates electricity to help identify the targeted nerve in your body. In some cases, the doctor might give you a mild sedative to help you relax, and will also numb the area with a local anesthetic to minimize discomfort.
After the target nerve is identified, the doctor will carefully insert a needle until it is positioned close to the nerve. This positioning is confirmed using the ultrasound, nerve stimulator or another device known as a fluoroscope, which helps the doctor see the inside of your body in real-time during the procedure.
If the doctor decides to use a nerve stimulator, they will continually adjust the needle and the electric current until the right response is achieved from the nerve. Achieving this correct response confirms that the needle is in the correct position.
Once the needle is placed correctly, the doctor may use a local anesthetic to temporarily block the nerve’s function to ensure the needle is appropriately placed. This is a diagnostic block. After this, the doctor will inject a special solution that contains phenol, a type of chemical compound.
Phenol injections can provide immediate relief from pain because it acts like a local anesthetic. It can also reduce muscle contractions and relax muscles, providing immediate relief from muscle spasms or stiffness. However, it’s important to know that the full benefits of phenol injections may not be felt for a few days after the procedure.
During and after the process, the medical team will closely monitor your heart and circulation to prevent or immediately address any complications. While the phenol starts working immediately, the full therapeutic effect may not be noticed until 24 to 48 hours later, and sometimes even up to 7 days. So, it’s important to remember to be patient and give the treatment time to work.
Possible Complications of Phenol Nerve Block
Like any other medical treatment or procedure, there can be some complications. These might include pain where the treatment was given, bleeding, and infection. In some cases, the procedure might accidentally damage the skin, muscles, blood vessels, and soft tissues around the treatment site.
If the treatment mistakenly ends up in a blood vessel, it could cause you to experience a ringing in your ears (tinnitus) and feel your skin warm up (flushing). Sometimes, part of a nerve responsible for sensation in your body might get damaged during the procedure causing it to regenerate in a painful manner. This can result in feelings of abnormal sensations or heightened sensitivity, which can be more uncomfortable than the original pain.
Rare but significant complications can also include lasting muscle weakness due to damage to a motor nerve or blood vessel, and trouble with bowel and bladder function as well as sexual function.
The body processes Phenol, the chemical used in this treatment, in the liver and eliminates it through the kidneys. Hence it’s typically avoided in patients who have serious liver disease. Long-term exposure to phenol can also cause kidney problems, skin lesions, and stomach issues. System-wide side effects may include nausea and vomiting, mental stimulation or an unusual sensation of excitement, and a slowed heartbeat.
Due to these potential side effects, some medical experts advise against the use of phenol in certain nerve-blocking procedures, especially those near major blood vessels. Side effects are not common if the administered doses are less than 100 mg.
What Else Should I Know About Phenol Nerve Block?
Research on the use of phenol neurolysis, a treatment that destroys certain nerves, is limited. Because no large controlled studies are available, we base our understanding on small studies, cases, observations, and opinions of experienced clinicians. Phenol neurolysis is usually a treatment of last resort, specifically for late-stage situations.
Phenol neurolysis can be used to treat muscle stiffness (spasticity) that results from conditions like stroke, traumatic brain injury, and spinal cord injury. The treatment involves injecting phenol into specific nerves, which can improve physical functions like walking. The treatment’s effects can last from a few weeks to months. In a review of 185 cases, it was most frequently injected into the obturator nerve (a nerve in the thigh), and the branches of the sciatic nerve that control the hamstring and adductor magnus muscles.
Phenol’s effects can last anywhere from 2 months to 2 years, depending on what condition is being treated. During this time, it’s beneficial to keep the limbs mobile to prevent stiffness in tissue.
Injecting phenol into the spine isn’t as common due to potential side effects. It’s mostly used for end-stage cancer patients to help manage pain and increase quality of life. However, it can result in loss of bowel and bladder function and weakness in the legs. Therefore, only a small number of cancer patients might be suitable for this treatment.
While phenol is widely known for managing pain, a study conducted among 42 patients with persistent non-cancer pain showed that using a 4% phenol solution can be effective and safe in certain cases, without causing major complications. However, phenol should only be used in select cases due to the risk of causing paralysis.
There’s ongoing debate about the effectiveness of different neurolytic treatments. Some believe that phenol is more potent than alcohol, while others believe it’s less intense and leads to more side effects. Studies have shown mixed results, but both have been effective in reducing muscle stiffness.
Despite its limitations, phenol remains a useful option for pain management. Though its use is quite limited, the most promising results have been seen in treating muscle stiffness and late-stage cancer. As we move forward, more large-scale trials should focus on the role of phenol neurolysis in managing muscle stiffness and weigh its cost-effectiveness compared to other treatment options.