Magnetic Field Interference with Adjustable CSF Shunts
Patients implanted with magnetic externally adjustable CSF shunt valves may have a very small risk of experiencing an unintended change in their valve setting when exposed to strong magnetic fields. The health consequences of unintended changes to CSF shunt valve settings include symptoms that, if unchecked, may become serious.
The FDA encourages health care providers to report all possible cases of unintended valve changes through the FDA MedWatch Program or through the FDA Medical Product Safety Network (MedSun) if your facility is an active participant in the MedSun program.
- The FDA believes all marketed CSF shunt systems are safe and effective when used as intended.
- To date, the FDA has no reported cases of death attributed to changes in CSF shunt valve setting due to magnetic field inference.
- The FDA does not currently advise patients with magnetic externally adjustable CSF shunt valves to avoid using specific electronic devices or magnets.
The FDA has conducted a systematic review of scientific literature published between January 1998 and October 2012. The literature review identified 83 non-MRI cases of CSF shunt valve changes possibly due to magnetic sources. Additionally, the agency has received Medical Device Reports (MDRs) potentially associated with this device problem. However, the prevalence of unintended changes in valve setting due to magnet interference is unknown.
While the risk appears to be quite small, patients should be aware that magnets may affect valve settings in magnetic externally adjustable CSF shunt systems.
FDA scientists are studying commonly used magnets and their field strengths to understand if and how they affect magnetic externally adjustable CSF shunt valves. Initial tests in FDA laboratories demonstrate that the unintended change of the CSF shunt system rapidly diminishes the farther away the magnetic source is from the CSF shunt. Although FDA’s initial findings are not comprehensive, they can be used as a basis for suggested safe distances between magnetic externally adjustable CSF shunt valves and magnetic sources.
Figure 2 illustrates several common magnetic sources. Preliminary studies have shown that these sources are safe if a distance of two inches or more is maintained between the magnet and the site of the implanted shunt valve, although differences in body physiology and magnet characteristics may affect the results.
Figure 2: FDA suggests keeping products that contain magnets two or more inches away from the location of magnetic externally adjustable CSF shunt valves. Patients are advised to use the ear opposite the shunt for devices requiring listening (e.g. cell phones, earbuds).