Pain expert Dr. Scott Fishman answers questions about cancer pain:

Q: When is a nerve-deadening block recommended?

A: Cancer pain often stems from growing tumors and injured tissue, so an effective block for it may be a neurolytic procedure, meaning a treatment to destroy nerves. Neurolytic blocks are appropriate only when the pain is clearly identified as coming from specific nerves. For instance, it makes sense for pancreatic pain but not for all-over bone pain.

The chemical used to kill nerves is usually either alcohol or phenol. Also, applications of focused amounts of heat (radio-frequency lesioning) or cold (cryoablation) may be used. Some clinicians have reported major pain relief from neurolytic blocks in fifty percent to ninety percent of cancer patients. The downside of damaging nerves is that the effect may persist only for several months. But for someone with a terminal illness, this can be a lifetime.

Neurolytic blocks can help pain stemming from various regions of the body as well as from internal organs. Intercostal blocks can help quell pain in the chest or abdominal wall, while peripheral blocks halt sensations coming from an arm or leg. These blocks, as with other cancer treatments, involve potential trade-offs.

For instance, a peripheral block for severe leg pain runs the risk of causing paralysis. But if a patient has only a short time to live and is in so much pain that he cannot move, stopping that agony by deadening nerves may be a compassionate trade-off. Neurolytic injections are a viable option when they offer a patient the best chance for dying without pain and without compromising quality of life.

Another technique for shutting off painful nerves is radio-frequency lesioning, which zaps an offending nerve and tissue with heat. The doctor uses a fine probe to reach the aggravating nerve and deliver a focused burst of heat through radio wave frequency. The placement and temperature of the probe control the size of the lesion.

Like other types of blocks, radio frequency does not require general anesthesia. However, it is not without risk. Killing nerves to quiet pain is often only a temporary cure. These delicate fibers often grow back and the average pain-free time from a radio-frequency lesion is about eight months.

So doctors do them with genuine concern about whether the benefits truly outweigh the risks, and they wonder whether the relief justifies the trouble of an invasive procedure. How does one judge the value of eight pain-free months? This is one of the current dilemmas in pain medicine. Even the best trained, most respected pain physicians have differing opinions about what to do in these tough cases.

A cousin of the radio-frequency lesioning technique is cryoanalgesia or the freezing of unruly nerves. Cryoanalgesia has been around for centuries. In its crudest form, it involves using cold to numb nerves. Its current, sophisticated form involves freezing and destroying nerves with a needlelike instrument called a cryoprobe.

The cryoprobe, like the probe used in radio-frequency lesioning, zeroes in on a single nerve. It incapacitates the nerve with intense cold derived from liquid nitrogen. If you have ever had a wart frozen, you are familiar with the freezing action of liquid nitrogen. Other chemicals, such as solutions of alcohol or phenol, also destroy nerves.

Nerve-destroying techniques such as radio frequency, cryoanalgesia, and alcohol usually are reserved for critical cases-patients with serious, if not terminal, illnesses like cancer.