Non-head MRI found safe in patients undergoing SNM

San Francisco-The therapeutic efficacy of sacral neuromodulation (SNM) was not affected by non-head magnetic resonance imaging (MRI) scans in a recent study.

"We evaluated 11 patients, and in this study we were able to demonstrate the safety of lumbosacral MRI with implanted SNM devices," Juan M. Guzman-Negron, MD, a second-year fellow in female pelvic medicine and reconstructive surgery at Cleveland Clinic, told Urology Times.

Historically, the use of MRI in patients with SNM devices has been contraindicated, said Dr. Guzman-Negron, working with Howard B. Goldman, MD, and colleagues. The findings were presented at the AUA annual meeting in San Francisco and subsequently published in the Journal of Urology (2018; 200:1088-92).

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Currently, the FDA has only approved a 1.5 Tesla MRI head scan in patients implanted with the InterStim II Neurostimulator. But few studies have examined the risk, other than a handful of retrospective studies that have shown no significant adverse events, Dr. Guzman-Negron said.

"Most studies were in the head and neck," he said. "Our study focused more on the lumbar area, which places the sacral neuromodulation device closest to the center of the body transmit coil, increasing the likelihood of radiofrequency energy transmission and heating compared to scans of other body regions."

To assess the risk, Dr. Guzman-Negron and colleagues first exposed a phantom model implanted with SNM to 1.5 Tesla lumbosacral and pelvic MRI scans and found that the risk of harmful heating was very low. To further investigate, the authors identified 11 patients with SNM implants who required lumbosacral 1.5 Tesla MRI.

They were all between 18 and 99 years of age, with a median of 75 years. Eight of the patients were women. All were implanted with a functioning InterStim II implantable pulse generator as a treatment for urgency urinary incontinence. All underwent lumbosacral 1.5 Tesla MRI. In six of them, the indication was lower back pain. The authors recorded stimulus settings and electrode impedances from the devices before and after the patients underwent MRI.

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One patient reported discomfort at the site of the implantable pulse generator during the MRI, but the discomfort disappeared after the scan. Two patients reported warmth at the site of the implantable pulse generator during the MRI, but also said that sensation ended with the scan.

None of the patients experienced stimulation or movement at the implantable pulse generator site, or any paresthesia.

Impedances and battery life only showed minimal changes during implantable pulse generator interrogation post MRI. Likewise, the authors found no changes in threshold amplitudes for sensation and localization of stimulation.

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There were no worsening scores in Urogenital Distress Inventory and Incontinence Impact Questionnaires 1 month after MRI. None of the patients reported a negative Patient Global Impression of Improvement score 1 month after MRI. Only one patient could recall pain, discomfort, movement, or abnormal stimulus during the MRI scanning.

Urologists planning MRI scans for patients with SNM implants should always consult with their respective hospital radiology department, Dr. Guzman-Negron recommended.