A phenol injection is a medical procedure that uses a chemical compound called phenol to create a nerve block. This treatment addresses severe muscle spasticity by interrupting the nerve signals that cause excessive, involuntary muscle contractions. The procedure offers a targeted approach to managing symptoms and improving a person’s functional abilities.
Conditions Treated with Phenol Injections
Phenol injections are used to manage severe muscle spasticity, a condition of high muscle tone and involuntary spasms resulting from neurological disorders. Conditions that lead to this spasticity include stroke, multiple sclerosis (MS), cerebral palsy, spinal cord injury, and traumatic brain injury. In these disorders, the communication pathway between the central nervous system and the muscles is disrupted.
The goals of treatment are patient-centered. For individuals with spasticity, these injections can lead to an improved range of motion in affected limbs and make stretching easier. This can, in turn, improve coordination and tolerance for wearing braces. By relaxing the persistently tight muscles, the procedure can also reduce pain, prevent permanent muscle shortening, and facilitate daily care activities like dressing and hygiene.
The Phenol Injection Procedure
The phenol injection is an outpatient procedure. To deliver the medication precisely, the physician first locates the nerve controlling the spastic muscle using ultrasound imaging or a nerve stimulator. A nerve stimulator sends a mild electrical impulse, causing the muscle to twitch when the correct nerve is found. This localization can take up to 30 minutes.
Once the target site is confirmed, a local anesthetic may be used to numb the skin. The phenol solution is then injected around the nerve. Because phenol has an immediate anesthetic effect, the injection itself is often not painful. Patients may also receive sedation, and a reduction in muscle tightness is noticeable immediately.
How Phenol Injections Work
Phenol is a neurolytic agent, meaning it causes a controlled injury to nerve tissue by denaturing its proteins. This process, known as neurolysis, disrupts the nerve’s structure. This interruption stops the flow of signals commanding the muscle to contract.
This provides a durable, though not permanent, block of the nerve signals. The effect is long-lasting because the nerve must regenerate to re-establish the connection. This results in a significant reduction in muscle tone and spasms for an extended period.
Risks and Post-Procedure Care
After a phenol injection, patients may have temporary pain, swelling, bruising, or a burning sensation at the injection site. These reactions are mild and resolve on their own. A less common risk is dysesthesia, an unpleasant burning sensation. This can occur if phenol affects nearby sensory nerves instead of the intended motor nerves.
Physical or occupational therapy is a standard part of post-procedure care. Therapists work with the patient to stretch the newly relaxed muscles and retrain the limb to use the improved range of motion. This therapy helps re-educate the muscles and prevent contractures, maintaining the functional gains from the procedure.
Phenol Injections vs. Botulinum Toxin
Phenol and botulinum toxin (Botox) are both options for treating muscle spasticity, but they work differently. Botulinum toxin acts at the neuromuscular junction where the nerve meets the muscle, blocking the chemical signal for contraction. In contrast, phenol works directly on the nerve itself, stopping the signal from traveling down the nerve fiber.
Phenol is often preferred for treating spasticity in larger muscles, such as those in the thigh or upper arm. Botulinum toxin is frequently used for smaller, more isolated muscles, like those in the hand or forearm. The duration of effect also differs; phenol’s effects can last for six months or longer, while botulinum toxin lasts for about three to four months.