Pain Medicine Specialties for Cancer Pain

Cancer pain, or advanced cancer pain is one of the main causes of suffering for patients with advanced cancer. At this stage, the patient is in considerable physical and mental agony, and a significant number of patients die not directly from cancer, but from severe pain. About 80% of advanced cancer patients have severe pain, and it is estimated that at least 15 million people in the world experience pain every day. Cancer pain has been recognized as a painful disease. Most cancer pain patients have improved pain relief through the three-step treatment principle (oral analgesic drugs mainly); however, some cancer pain patients still have severe pain after strictly applying the “three-step drug treatment program”, or are unable to fully accept the treatment of the “three-step program” due to inability to eat, contraindications to medication, inability to tolerate the side effects of analgesic drugs, and the excessive economic burden of taking the medication, etc. These patients are known as intractable cancer pain or refractory cancer pain, and they are the most common forms of cancer pain in China. Intractable cancer pain or refractory cancer pain are all indications for nerve-destructive block. Nerve-damaging blocks provide an excellent way to manage chronic cancer pain. The success of these nerve blocks depends on the patient’s understanding and cooperation, the acceptance of other departments (e.g., oncology), and the experience and skill of the pain physician, who, after proper training and manipulation, has improved the safety of the treatment with the precise guidance of imaging equipment (CT, C-arm). Commonly used methods are as follows: Peripheral nerve disfiguring block When cancer pain is more limited and the application of medication is not effective, blocking the peripheral nerves with different concentrations of phenol, ethanol, adriamycin, and mitomycin solutions, or disfiguring the nerves with radiofrequency, often results in a satisfactory efficacy. The role of peripheral nerve release in the treatment of pain due to malignant causes is clear and certain, although there are limitations; to ensure effective analgesia, the nerve block must be located proximal to the source of the irritation. It can be performed on an outpatient basis or in the patient’s home. It is mainly used for those with more limited pain or residual localized pain after blocking with other methods. Commonly used nerve blocks include the maxillary nerve, mandibular nerve, auriculotemporal nerve, greater occipital nerve, suprascapular nerve, thoracic nerve, intercostal nerve, femoral nerve, obturator nerve, sciatic nerve, and peroneal nerve. Subarachnoid nerve disfiguring block Subarachnoid phenol or ethanol block has superior analgesic effect and duration than local nerve block and nerve root block. This method is effective in controlling cancer pain but requires an experienced anesthesiologist. Phenol-glycerol block is more commonly used at present. The analgesic effect accounts for 50%~60%, 21%~30% and 18%~20%. The effect is closely related to the tumor location, the puncture gap, the injection dose and the method of pain evaluation. Most of the reported pain relief lasts from 2 weeks to 3 months, and in a few patients it lasts from 4 to 12 months. Complications after block are mainly caused by damage to non-nociceptive nerves. All treatment should be performed in the operating room. Complications of bilateral blocks include urinary retention, rectal dysfunction, and muscle paralysis, which most often lessen or disappear within a week. Epidural nerve-destroying block Epidural block is a method of blocking spinal nerve conduction by injecting nerve-destroying drugs into the epidural space to produce segmental analgesia. Compared with peripheral nerve block, epidural block can block somatic and autonomic nerves at the same time, blocking a larger range, and the effect is accurate; compared with subarachnoid block, it can avoid meningeal irritation and spinal cord or spinal nerve injury, and because the nerve-destroying drug does not directly contact the nerve root, it is outside the dura mater to play a role, therefore, the possibility of bladder and rectal sphincter involvement is less than the possibility of subarachnoid block, but the effect is not as good as that of subarachnoid block. However, it is not as effective as subarachnoid block. In addition, nerve-destroying agents can be injected in divided doses through an epidural catheter. Abdominal plexus ethanol block Abdominal plexus ethanol block for the treatment of pain caused by abdominal tumors, especially pancreatic cancer pain, can be pain-free in about 60-85% of patients. It needs to be performed under X-ray fluoroscopy. Abdominal plexus blocks provide excellent relief of epigastric pain and back involvement pain caused by malignant tumors of foregut origin. It is most commonly used for pancreatic cancer, which, contrary to conventional wisdom, is most commonly characterized by pain rather than painless jaundice.NCPB is also effective for neoplastic pain in the distal esophagus, stomach, liver, bile ducts, small intestine, proximal colon, adrenal glands, and kidneys. Abdominal plexus block should be considered for pain caused by intra-abdominal malignant tumors that have been poorly treated with other methods. Abdominal plexus block has been reported to be effective for colon and rectal cancer pain as well. In conclusion, some cancer pain patients have to face dozens or hundreds of analgesics every day, but still cannot effectively relieve pain or cannot tolerate the side effects, enduring both physical and mental pain, and they are often disturbed by the inappropriate treatment methods, hoping that a miracle will happen. Nerve-destroying block provides an excellent way to control chronic cancer pain.