Neurolysis is the application of chemical or physical agents to a nerve to cause a temporary or permanent degeneration of targeted nerve fibers. When the nerve fibers degenerate, it interrupts the transmission of nerve signals. If these nerve fibers are carrying nociceptive signals, it can, therefore, provide pain relief. The most frequently employed modes of neuroablative therapy: radiofrequency (heat), chemoneurolysis (chemical), and cyroablation (cold)[Zhou et al.]. Neuroablative procedure and neuraxial neurolysis, in particular, has been described for cancer pain. Refractory pain management at the end of life is an enormous public health problem affecting at least 10 to 15% of cancer patients. Options beyond the WHO analgesic ladder can play a significant role to relieve suffering and improve side effects in select patients.Neuroablation by chemical and thermal neurolysis or surgery can provide long-term control of severe cancer pain without substantial adverse effects.
Intrathecal chemical neurolysis (ICN) is an essential intervention in the treatment of cancer pain. Dogliotti first described intrathecal neurolytic blocks for chronic cancer pain in 1931. In recent years, alcohol and phenol have been the substances most commonly used for this purpose. No randomized control trials exist that evaluate the effectiveness of this intervention, so the literature consists of observations, reports and book chapters reflecting the opinions of experienced clinicians. Neuraxial neurolysis is dangerous, but when used appropriately in carefully selected patients, it is effective, inexpensive, quickly accomplished, and associated with a low incidence of severe morbidity. In appropriately selected patients neuraxial neurolysis can decrease opioid usage and improve the quality of life.The use of neuraxial neurolysis has decreased in recent years due to other interventional treatments in terminal cancer. Neuraxial neurolysis has the advantage of providing immediate analgesia and pain control. It might also be especially useful in developing countries because unlike many other interventional techniques it doesn’t require C-arm or imaging and fewer follow-up visits.
The meninges protect the spinal cord. Three layers cover the spinal cord which includes the dura mater, arachnoid mater and pia mater, from outermost to innermost covering. The epidural space is a potential space that exists between dura and vertebrae. Subarachnoid space exists between arachnoid and pia. Cerebrospinal fluid (CSF) exists in subarachnoid space. Pia mater tightly covers the spinal cord. The epidural space surrounds the dural sac and continues from foramen magnum superiorly to the sacral hiatus inferiorly. This space is protected by the posterior longitudinal ligament anteriorly, and posteriorly by the ligamentum flavum and the periosteum of laminae. The integral elements of the spine are supplied by the dorsal rami of the spinal nerves, and by the sinuvertebral nerves. Neuraxial space is approached by placing a needle between vertebrae and injecting medication into the epidural space (for epidural anesthesia) or the subarachnoid space.  Subarachnoid neurolysis is usually reserved for pain restricted to two or three dermatomes, except in some instances with existing loss of bowel, bladder, and motor control. Epidural neurolysis may be useful for pain that bilateral and multiple levels.
Appropriate patient selection is essential. Neuraxial neurolysis can be helpful in intractable cancer-related pain when pharmacological analgesic therapy including opioids and antitumor therapy has failed to control pain. Its indication is for pain that is primarily somatic in origin. Visceral or neuropathic pain treatment is less reliable with spinal neurolytic procedures than somatic pain.
In addition to patient refusal and coagulopathy, contraindications to this procedure include an inadequate response to neuraxial local anesthetics although this does not always successfully predict the outcome. This procedure is not reserved for deafferentation or sympathetically mediated diffuse pain.
A 24-gauge pencil point needle is needed. A smaller needle might disrupt the free flow of CSF.
An interventional pain physician performs this procedure. In the United States, an interventional pain physician completes a one-year ACGME accredited fellowship after finishing four-year training in anesthesiology, neurology or psychiatry residency.
The patient should have adequate intravenous access before starting the procedure. This procedure requires continuous communication with the patient, and thus, the use of sedation or hypnotic is not ideal. An assistant should help with positioning and checking the vitals at regular intervals. The patient is prepped and draped in a sterile manner.
Agents including alcohol, phenol, and botulinum toxin are all choices for chemical neurolysis. Alcohol produces nonselective destruction of the cholesterol, phospholipids, and lipoproteins. At least a 35 to 60 % concentration is needed. It also spreads rapidly from the injection site so that large volumes are often necessary. Phenol 5% to 7% is a common agent, and it dissolves the axons and Schwann cells inside the basal lamina tubes.
Usually, the practitioner advances a 24-gauge pencil point needle into subarachnoid space. In intrathecal neurolysis, needle tip placement is at the vertebral level where the target dorsal root leaves the spinal cord and not where it passes the intervertebral foramen. It is crucial to prevent a leak of the alcohol or phenol to unintended nerve roots.
Phenol is hyperbaric relative to CSF, and this principle is harnessable by positioning patients with the painful side dependent. Alcohol is hypobaric relative to CSF and hence to facilitate the spread of alcohol to the target area, the patient should be positioned lateral decubitus with the painful side up. Typically, alcohol causes a burning sensation on injection while phenol has local anesthetic properties and often causes a warm sensation on injection. The concentration of phenol and alcohol in CSF diminishes rapidly after administration. The patient should be maintained in this position for at least 30 minutes after the injection.
Epidural neurolysis is a less common procedure for neuraxial neurolysis. In epidural neurolysis, the needle or catheter tip lies closer to the vertebral level that corresponds to the dermatomal level of pain. This procedure involves the insertion of an epidural catheter, and repeated injections performed over a few days.
Neuroablation can lead to the development of deafferentation pain, which is why indications for neuraxial neurolysis are primarily for patients with less than a year life expectancy. Neuraxial blockade might decrease the quality of life of the cancer patient by inducing motor weakness, incontinence, sexual dysfunction or loss of position sense. Reports of bowel paresis occur in less than 1 percent of patients. There is less risk of complications mentioned above with epidural neurolysis compared with subarachnoid neurolysis. There is also the risk of post-dural puncture headache.
An analysis of 5020 patients in fifteen case series revealed that 60% of patients reported good pain relief while 22% reported moderate pain control with alcohol as a neurolytic agent. Similarly, a review of 1982 patients in twelve case series with phenol showed that 58% patient reported good pain control while one fourth reported poor pain control. This low resource interventional technique helps with the quality of life of terminal cancer patients who usually have few other options. It is, however, important that patients have a realistic expectation and understanding of the side effects and complications. Large randomized control trials are needed to determine the efficacy of neuraxial neurolytic techniques compared to other interventions in cancer pain patients.
An interprofessional team that provides a holistic and integrated approach to cancer pain care can help achieve the best possible outcomes. A cancer patient is often first seen by a primary care or advanced practice nurse provider who refers the patient to an oncology center where for evaluation by an oncologist. The radiologist frequently performs radiological imaging including MRI and CT scan for the staging of terminal cancer. The imaging studies are vital for the interventional pain physician in planning the neuraxial neurolysis. While neuraxial neurolysis is not recommended unless the patient has less than one year of expected life, early involvement of an interventional pain physician in patient care can optimize the planning and achieve best outcomes. Many patients are referred by physicians who erroneously believe that neurolytic blocks are permanent and without significant risk. There is a need to introduce an all-inclusive pain and palliative care model at all levels of the healthcare system. All stakeholders including oncology services, palliative care, and pain management should be involved in decisions involving neuraxial neurolysis. A multidisciplinary approach to issues such as determining patient life expectancy or immunosuppression while attempting an interventional procedure is vital to patient safety. Hence a team-based approach to optimum pain care is therefore critical for improving the quality of life of patients with terminal cancer.
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