August 2023 issue, BioElectRx Business Report
August 31, 2023 | Earlier this year, the number of patients implanted with sacral nerve stimulation devices reached 400,000, including more than 380,000 patients implanted with Medtronic’s InterStim system and more than 20,000 implanted with Axonics’ SNM devices. Reaching this milestone provides us with an occasion to reflect on safety of SNS devices.
As analyzed in a recent review, since 2016, there has been a steady decrease in the number of adverse events reported in the FDA Manufacturer and User Facility Device Experience database. The decrease is ongoing despite Axonics’ entry into the SNS market in 2020 and a large increase in eligible patients after FDA’s approval of MRI‐compatible SNS devices in the same year, suggesting that implanting surgeons are getting more experienced over time.
Among the most common adverse events reported in MAUDE, 190 concern a loss or lack of device efficacy, 96 involve device failures unrelated to the battery, 81 relate to stimulation-unrelated pain, 67 to wound complications, 64 to stimulation-related pain, 47 to device or lead migrations, and there were 46 device failures related to battery.
Since the U.S. is the largest market for SNS devices, we can estimate that about 300,000 devices were implanted in this country. Relative to that, we have a total of 591 MAUDE-reported events, representing about 0.2% of implanted patients. This percentage is very low in comparison with DBS and SCS, which is not surprising given that the SNS implantation procedure is considerably simpler, as it does not breach the blood-brain barrier and presents no risk of CSF leakage or CSF infection. The SNS lead readily slides into a bony sacral foramen, while DBS and SCS leads are inserted either inside or on top of delicate neuronal tissue that is susceptible to damage. Incidence of lead migration in SNS is less than 0.1% due to its use of anchoring tines in the muscle tissue, compared with 1.7% for SCS leads that lack anchoring tines.
Beyond the MAUDE statistics, SNS therapy also shines in scarcity of litigation. Only four lawsuits were filed for Medtronic InterStim devices, including these reasons: 1) persistent pain after device removal, 2) pain and infections post-implantation, 3) alleged improper technique of device implantation, and 4) device malfunction leading to its removal. In comparison, a transvaginal mesh, another implantable device for treating overactive bladder, was a subject of the class action lawsuit in Australia against Ethicon, in which 6% of implanted patients experienced considerable complications that required surgical intervention.
It is worth mentioning that SNS therapy for bladder and fecal incontinence involves 24-hour continuous stimulation, while forthcoming SNS therapies for auto-immune disorders and other bioelectronic medicine indications are likely to use intermittent stimulation, which should further improve SNS safety.
