Neurolytic blocks are indicated for patients with severe, intractable cancer pain in whommore conventional therapy proves inadequate or conventional analgesic modalities are accompanied by unacceptable side effects. The most common chemical neurolytic techniques utilized for cancer patients are celiac plexus, lumbar sympathetic chain, hypogastric plexus, and ganglion impar blocks. Chemical neurolysis may also occasionally be used in patients with refractory benign neuralgia and, rarely, in patients with peripheral vascular disease. These blocks can be associated with considerable morbidity (loss of motor and sensory function), so patients must be selected carefully, and only after thorough consideration of alternative analgesic modalities. Moreover, although the initial result may be excellent, the original pain may recur, or new (deafferentation or central) pain will develop, in a majority of patients within weeks to months.
Temporary destruction of nerve fibers or ganglia can be accomplished by injection of alcohol or phe-nol. These neurolytic agents are not selective, affect-ing visceral, sensory, and motor fibers equally. Ethyl alcohol (50–100%) causes extraction of membrane phospholipids and precipitation of lipoproteins in axons and Schwann cells, whereas phenol (6–12%) appears to coagulate proteins. Alcohol causes severe pain on injection, thus local anesthetic is usually administered first. For peripheral nerve blocks, alcohol may be given undiluted, but for sympathetic blocks in which large volumes are injected, it is given in a 1:1 mixture with bupivacaine. Phenol is usually painless when injected either as an aqueous solution (6–8%) or in glycerol; a 12% phenol solution can be prepared in radiopaque contrast solution.
Neurolytic celiac plexus or splanchnic nerve blocks may be effective for painful intraabdominal neo-plasms, especially pancreatic cancer. Lumbar sym-pathetic, hypogastric plexus, or ganglion impar neurolytic blocks can be used for pain secondary to pelvic neoplasms. Neurolytic saddle block can provide pain relief for patients with refractory pain from pelvic malignancy; however, bowel and blad-der dysfunction should be expected. Neurolytic intercostal blocks can be helpful for patients with painful rib metastases. Additional neurodestructive procedures, such as pituitary adenolysis and cor-dotomy, may be useful in end-of-life palliative care.
When considering any neurolytic technique, at least one diagnostic block with a local anesthetic solution alone should be used initially to confirm the pain pathway(s) involved and to assess the potential efficacy of the planned neurolysis. Local anesthetic solution should again be injected immediately prior to the neurolytic agent under fluoroscopic guidance. Following injection of any neurolytic agent, the nee-dle must be cleared with air or saline prior to with-drawal to prevent damage to superficial structures.
Many clinicians prefer alcohol for celiac plexus block and phenol for lumbar sympathetic block. For subarachnoid neurolytic techniques, very small amounts of neurolytic agent (0.1 mL) are injected. Alcohol is hypobaric, whereas phenol in glycerin is hyperbaric; the patient undergoing subarachnoidneurolysis is carefully positioned so that the solu-tion travels to the appropriate level and is confined to the dorsal horn region following subarachnoid administration.
Cancer patients frequently receive anticoagula-tion therapy if they are at elevated risk for venous thromboembolic phenomena. When such a patient has discontinued anticoagulant medication in prep-aration for a diagnostic local anesthetic block, it may be more practical to obtain consent for a neurolytic procedure in advance and to follow the diagnostic block immediately with chemical neurolysis if the diagnostic procedure has resulted in pain relief.