CDRH Instructs on Magnetic Field Interference with Shunt Systems

Regulatory NewsRegulatory News | 16 July 2019 |  By 

Magnetic externally programmable cerebrospinal fluid (CSF) shunt valve settings can inadvertently change when at a distance of fewer than two inches from common magnetic sources such as cell phones, a US Food and Drug Administration (FDA) analysis concludes.
FDA’s Center for Devices and Radiological Health (CDRH) reports that exposure to strong magnetic fields from either external magnetic sources or magnet-containing hearing devices like cochlear implants could result in unintended changes to valve settings in implanted patients.
A letter to health care providers cautions on over or under-drainage of CSF if programmable CSF shunt valves interfere with environmental sources of magnetic fields, including cell phones, tablets, headphones, cordless drills and metal detectors, or with adjacent hearing devices that contain magnets. Valve setting changes from magnetic interference may lead to altered mental status and headaches, among other symptoms that can become more serious if left untreated.
CDRH underscores the limitations in the totality of the available data in citing both an analysis from 2019 and another conducted between January 1998 and October 2012 that show data are lacking for the agency to fully understand the extent of the problem with magnetic interference.
“There is a risk of unintended changes in a programmable CSF shunt valve setting due to magnet interference” but “the prevalence is unknown,” the agency reports on a new webpage. Its findings “were not comprehensive” but “can be used as a basis for suggested safe distances between magnetic externally programmable CSF shunt valves and magnetic sources.”
FDA recommends keeping magnet-containing products at least two inches away from the location of the shunt and using the ear opposite the shunt when using products like cell phones.
FDA’s letter to health care providers lists elements to include in adverse event reports of unintended valve setting change incidents, such as “details of the resetting event” and the suspected magnetic source(s), among others.
“Clinicians play a critical role in conducting safety checks, assessing the performance of these devices, and reporting issues that impact their performance,” the agency stresses in another new webpage. “Prompt reporting of adverse events can help the FDA identify and better understand the risks associated with medical devices.” The letter to health care providers also offers recommendations specific to positioning the shunt when patients have other implanted devices that contain magnets.


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