Nerve-Freezing Technique Staves Off Post-Mastectomy Pain

NEW ORLEANS -- Percutaneous cryoneurolysis applied immediately before breast surgery helped to control acute pain and stop the progression to chronic pain, according to one center's pilot study.

Adults randomized to cryo before unilateral or bilateral mastectomy reported median zero pain (on a pain rating scale from 0 to 10) on postoperative day 2. In contrast, controls who received sham treatment reported a higher median pain score of 3.0 at that point (P<0.001), reported Brian Ilfeld, MD, MS, of the University of California San Diego.

His group found more evidence of superior analgesia with cryoneurolysis over sham:

• Large reduction in cumulative opioid use in the first 3 weeks: 1.5 mg vs 72 mg (P<0.001)
• More patients reporting an opioid-free year after surgery: 50% vs 14% (P<0.001)
• Reduced development of chronic pain by 1 year: 3% vs 17% (P<0.001)

Results of the small 60-person study were presented by Ilfeld at this year's American Society of Anesthesiologists (ASA) meeting, with the full study published in Anesthesiology.

Notably, percutaneous cryoneurolysis was associated with reduced phantom breast pain as well.

Guided by ultrasound, the procedure comprises a reversible ablation of a peripheral nerve using a cold ice ball on the probe. The target nerve's axons are expected to regrow in about 1 to 3 months. The cryo technology has been around since the 1980s and is FDA cleared for acute and chronic pain, according to Ilfeld.

No cryoneurolysis-related systemic side effects or complications were reported in the pilot study.

"Cryoneurolysis avoids the systemic side effects related to opioid use, such as nausea, sedation, and respiratory depression, and it has no potential for misuse‚ dependence‚ overdose, or diversion. Unlike continuous peripheral nerve blocks, cryoneurolysis has no risk of local anesthetic-induced cardiac/neurologic toxicity, myotoxicity, catheter dislodgement, local anesthetic leakage, or infusion pump malfunction," Ilfeld and colleagues wrote.

The optimal freeze and defrost durations and numbers of freeze-defrost cycles are still unknown, however.

Perhaps more importantly, the "loudest note of caution" against wider adoption of cryoneurolysis is related to the potential for chronic neuropathic pain, noted a trio led by James Rathmell, MD, of Brigham and Women's Hospital and Harvard Medical School in Boston, in an accompanying editorial.

Ilfeld acknowledged to the ASA audience that his group did not differentiate between neuropathic versus non-neuropathic pain in the study.

"Although our patients might easily live with some persistent numbness, it is more to ask of them to live with persistent allodynia," Rathmell and colleagues wrote. "Given extensive preclinical literature and some hints from the clinical literature that neuropathic pain may occur after cryoneurolysis, is it reasonable to ask patients to take this potential risk, even if such nerve injury-induced hyperalgesia and allodynia are rare?"

"We are keenly interested in the replication of these promising findings in larger cohorts of patients, to truly assure that this nerve injury-based treatment does not introduce a new source of neuropathic pain in a subgroup of vulnerable patients," they added.

For this randomized study, patients scheduled for mastectomy were randomized to active (n=31) or sham (n=29) ultrasound-guided percutaneous cryoneurolysis of the ipsilateral T2 to T5 intercostal nerves. Participants all received a continuous paravertebral block with ropivacaine 0.2% until the early morning of discharge.

The study cohort had a median age of 43 years and was comprised of all women. The main baseline difference between groups was that the cryo recipients underwent fewer nymph node dissections; adjusting for this did not materially change the main findings of the study, Ilfeld and team said.

Ilfeld acknowledged the limited generalizability of such a small single-center study, and noted that the investigator applying cryoneurolysis could not be blinded to treatment.

Moving forward, Ilfeld said that his group is pursuing research on cryoneurolysis for traumatic rib fractures.