Laird Harrison

April 23, 2014

SAN FRANCISCO — Fewer than half of patients given a trial of spinal cord stimulation go on to have the treatment permanently, a new US national survey shows.

The 41.4% "conversion" rate in the study — that is, conversion from trial to permanent spinal cord stimulation — is much lower than the 63% to 91% rate reported from previous studies.

"We also found significant regional variation, with North-Central and South regions having significantly higher conversion rates than the Northeast or West," said lead author Gustavo Chagoya, a medical student at Duke University in Durham, North Carolina.

Chagoya presented the findings here at the American Association of Neurological Surgeons (AANS) 82nd Annual Meeting.

Increased Scrutiny

Before implanting spinal cord stimulators, clinicians typically test whether stimulation will reduce patients' intractable neuropathic pain.

The trials must show that stimulation reduces the patient's pain by 50% or reduces the patient's use of analgesic medications by 50%, and provides some functional improvement.

Recently insurance providers have scrutinized healthcare providers whose ratio of trials to implants is less than 50%. Some insurers have begun limiting coverage for each patient to 1 trial per anatomic region for the patient's lifetime.

As a result, researchers are trying to pinpoint exactly which patients are most likely to benefit from the treatment.

Previous studies have shown that patients with multiple pathologies have lower conversion rates. However, each of the studies Dr. Chagoya and his colleagues found in the literature used data from single institutions.

To find out which spinal cord trials are resulting in implants nationwide, the Duke researchers analyzed data from MarketScan, a database that contains longitudinal patient billing data for 170 million patients from 2000 to 2009.

Patients having a percutaneous implantation of neurostimulation electrode array (Current Procedural Terminology [CPT] code: 63650) without simultaneous implantation of a permanent pulse generator (CPT: 63685) were selected for this analysis. Patients were analyzed for predictors of successful conversion according to age, sex, insurance status, employment status, geographic location, number of previous percutaneous trial attempts, and primary diagnosis. The most common indications were radiculitis/neuritis (43.8%) and postlaminectomy syndrome (38.6%).

The researchers defined a conversion as successful if a patient received an implant within 3 months.

Their findings are as follows:

  • A total of 21,672 patients had percutaneous trials. Of these, 8982 converted, yielding a conversion rate of 41.4%.

  • The median age of those who converted and those who did not was the same: 54 years. But only 38.3% of those over 65 converted, compared with more than 42% of younger patients. This was statistically significant (P < .0001).

  • The conversion rate for women, 41.7%, was not statistically different from the rate for men.

  • Patients with commercial insurance had a 43% conversion rate, compared with the 36.8% rate among those without commercial insurance, a statistically significant difference (P < .0001).

  • The condition of the patients as measured by the Charlson Comorbidity Index did not significantly differ.

  • Among those who had never had a trial before, 44% converted, while among those with 1 previous trial, 29% converted; among those with 2 or more trials, 14% converted. These differences were statistically significant (P < .0001).

  • Regional differences were also statistically significant (P < .0001).

Table. Regional Differences

Region Successful Conversion (%)
Northeast 36.1
North Central 44.5
South 42.9
West 36.6


Chagoya acknowledged some weaknesses in the study. It is a retrospective review. The diagnostic procedure codes reported in the database may not always be accurate, he noted, and the database did not include the patients' preoperative and postoperative status.

Asked to comment, session moderator Jason W. Schwalb, MD, told Medscape Medical News that this analysis of the MarketScan database adds to the understanding of spinal cord stimulation.

"The advantage is that it combines not just the academic centers but private practices and across a broad swath of specialties," he said. "So it gives a little better idea than what we have seen in the literature."

Mr. Chagoya and Dr. Schwalb have disclosed no relevant financial relationships.

American Association of Neurological Surgeons (AANS) 82nd Annual Meeting. Abstract 816. Presented April 9, 2014.


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.