Cooled RFA: New Option for Painful Metastatic Bone Tumors

Nagy Mekhail, MD, PhD

A new radiofrequency ablation (RFA) technique uses a bipolar water-cooled RFA probe to treat pain related to metastatic bone tumors when such pain is unresponsive to conventional methods. Clinical experience with cooled RFA (OsteoCool® RF Ablation System) at Cleveland Clinic shows local disease control, marked pain reduction and quality-of-life improvements from a single treatment, says Nagy Mekhail, MD, PhD.

Up to 30 percent of patients with metastatic bone tumors do not respond to palliative measures involving radiation therapy, chemotherapy, surgical excision or conventional RFA. Most RFA systems were designed for use in soft tissue, employing a monopolar technology. They do not perform consistently in bone because bone is not a good conductor of electrical energy and heat. The current from the single probe tip takes the path of least resistance to a grounding pad on the patient's leg, explains Dr. Mekhail, Director of Evidence Based Medicine in the Department of Pain Management.

"Ideally, we'd like to produce a big lesion by burning the tumor and the surrounding trabecular bone," he says. "Ablating the free nerve fibers can alleviate pain caused by vertebral body metastases."

Current RFA systems produce lesions confined to the active tip. An internally cooled RFA probe lowers tissue impedance, increasing the radius of effective heating. Internal cooling eliminates the tissue charring that is common with conventional RFA. Transmission of RF waves ceases in charred tissue, limiting the size of the intervertebral lesion. The bipolar tip on the OsteoCool device localizes heating within cortical bone, eliminating the need for a grounding pad and reducing risk of damage to surrounding tissue.

"The lesion created by water-cooled RFA is spherical and extends beyond the probe tip on both sides," says Dr. Mekhail. "It is eight times greater by volume than the thermal RFA lesion produced by a similar length probe. A large spherical lesion can effectively ablate the metastatic tumor and the free nerve endings that are causing the pain."

The treatment is performed on an outpatient basis. Patients who have vertebral fracture as a tumor complication can undergo kyphoplasty in conjunction with cooled RFA.

To date, 11 patients have been treated with the OsteoCool system at Cleveland Clinic and the University of Washington in Seattle. Three patients who presented with severe low back pain despite opioid therapy — two with metastatic breast cancer to the L3 vertebral body, and one with vertebral metastasis secondary to prostate cancer — have been treated at Cleveland Clinic. All achieved a 75 percent reduction in pain on the visual analog scale as well as decreased disability and improved function, with an 80 percent improvement in Pain Disability Index score. Improvements were maintained at two- and six-month follow-up.

Enrollment in a study to test the Osteo-Cool system's efficacy and safety in 15 patients with spinal metastases will begin at Cleveland Clinic soon, says Dr. Mekhail.

Precise Method of Spinal Cord Stimulation Promises Better Control of Lower Extremity Pain

Samuel Samuel, MD

Though spinal cord stimulation has been used to treat chronic pain since the 1970s, it often fails to control lower extremity pain because of the difficulty of targeting the specific anatomic sites involved. Dorsal root ganglion (DRG) stimulation is emerging as an option with the ability to more precisely stimulate anatomic targets implicated in chronic pain — even in the lower extremities. So says Samuel Samuel, MD, a pain specialist leading a study of DRG stimulation in the Department of Pain Management.

Patients with lower extremity pain, such as neuropathy or postlaminectomy syndrome (failed back surgery syndrome), appear to be the best candidates for DRG stimulation, which has been in clinical use in Europe for the past few years. Single-center pilot studies and case studies have been conducted in the United States, in preparation for a multicenter trial for which Cleveland Clinic is enrolling patients.

The DRG is located within the spinal foramen and contains cell bodies of the primary neurons. “We are just beginning to understand the DRG’s function and its mechanism for modulating the pain signal,” says Dr. Samuel. “The DRG receives information from the extremities or the trunk and conveys it to the brain, acting as a gatekeeper. It magnifies or diminishes the pain signal depending on the information it gets. It’s a highly complex structure.”

Discrete stimulation of one side or one level of the spinal column is sometimes hard to achieve with conventional spinal cord stimulation, which may explain some treatment failures with conventional stimulation. Preferentially targeting the primary sensory neurons responsible for chronic pain in the lower extremities — which DRG stimulation makes possible — can improve the outcomes obtained with neuromodulation.

“For instance, we can precisely stimulate the left thigh or the right foot if needed,” explains Dr. Samuel. “The advantage is the ability to stimulate one or two levels of the spinal column, and one or both sides.”

Candidates for DRG stimulation undergo a trial stimulation period of up to two weeks. If they experience 50 percent or greater improvement in pain, electrical leads and contacts are placed permanently using a minimally invasive epidural approach, and the leads are attached to a neurostimulator. The procedure is performed on an outpatient basis.

Cleveland Clinic seeks to enroll 20 patients with chronic intractable leg pain with or without back pain in the multicenter clinical trial. The principal investigators at Cleveland Clinic are Dr. Samuel and Nagy Mekhail, MD, PhD.

To refer a patient for enrollment, call 216.636.0103.

Analgesic Cell Therapy Could Be a Game-Changer in Chronic Pain

Jianguo Chen, MD, PhD

Stem cell research underway at Cleveland Clinic could someday dramatically change the way chronic pain is treated and decrease the potential for prescription drug abuse.

The research is in the early stages of testing whether mesenchymal stem cells, after being harvested from a patient’s bone marrow and reprogrammed into chromaffin like cells, can provide relief from chronic intractable pain when they are transplanted back into the same patient.

The endogenous opioids that are generated from these differentiated chromaffin-like cells have powerful analgesic effects. In fact, they have the potential to treat nerve injury-induced pain that usually doesn’t respond to exogenous opioids such as morphine and its derivatives, according to Jianguo Cheng, MD, PhD, principal investigator of the Department of Defense (DoD)-funded study and Professor and Director of Cleveland Clinic’s Pain Medicine Fellowship Program.

Dr. Cheng and his collaborator, Tingyu Qu, MD, PhD, from the University of Illinois at Chicago, developed the patent pending technology to differentiate the autologous stem cells into chromaffin-like cells. Initial animal studies have already demonstrated the feasibility of transplanting the cells for pain relief.

The current DoD study in rats is testing safety, analgesic effects and anti-tolerance effects, as well as the longevity and stability of the cells once transplanted. “While many more studies are needed over many years before this approach can be tested in humans, initial results from animal studies have shown great promise,” says Dr. Cheng. In addition to patients with intractable neuropathic pain, patients with cancer pain could someday be good candidates for this therapy.

If the stem cell therapy is found to be safe and effective, potential advantages include:

  • Therapeutic alternative — This approach promises the ability to treat intractable neuropathic pain in patients who don’t respond to prescription opioids.
  • Fewer side effects — Patients who opt for analgesic cell therapy could avoid the side effects of exogenous opioids, such as respiratory depression, immunocompromise, disruption or depression of endocrine functions, constipation, vomiting and itching.
  • Decreased abuse — Endogenous opioids from analgesic cell therapy serve as an alternative to highly addictive prescription opioids, which cause more deaths than car accidents and are often diverted for illegal use.
  • Reprogrammed stem cells — Unlike embryonic stem cells, once the mesenchymal stem cells are differentiated into chromaffin-like cells, they can’t grow or divide, so tumor risk is not an issue.

If found to be viable, analgesic cell therapy has the potential to be a gamechanger. As stated in the DoD’s assessment of the grant application, “This approach to pain management is very innovative and, if successful, could have a tremendous impact on the way that chronic pain is treated.”