- Magnetic interactions between devices can cause complications for patients who have both a programmable cerebrospinal fluid shunt (CFS) and a hearing implant, FDA said in a letter Tuesday to healthcare providers.
- The magnetic field interference may cause unintended changes to the shunt valve settings, resulting in over- or under-drainage of the cerebrospinal fluid, the agency said.
- Altered shunt valve settings could lead to a host of problems, ranging from altered mental status and headache to difficulty walking. If untreated, the symptoms could progress to loss of consciousness, seizures, hemorrhage or even death, FDA cautioned.
FDA wants to increase awareness of the potential risk for magnetic interference when patients have both a shunt and an implanted hearing device. The agency has determined there is a risk of unintended changes in a programmable CSF shunt valve setting due to magnet interference, but it's unknown how frequently they occur.
The shunts are used to treat hydrocephalus, a buildup of fluid in the brain that has many causes, including head injury, stroke, infection, tumors and bleeding. The risk is to the shunt patient who also has a hearing implant that contains magnets. Devices that could cause magnetic interference with a programmable shunt include cochlear implants, bone conduction hearing devices and middle ear hearing devices.
FDA conducted an analysis between January 1998 and October 2012 of the possible interaction between programmable CSF shunt valves and external sources that use magnets, such as cell phones, electronic tablets, cordless power drills, headphones and earbuds. The agency found a risk of experiencing an unintended change in valve setting when exposed to strong magnetic fields.
The agency said the studies showed the risk of change to the shunt system rapidly diminishes the farther away the magnetic source is from the CSF shunt. Although the findings were not comprehensive, they can be used as a basis for suggested safe distances between externally programmable CSF shunt valves and magnetic sources, the agency said.
In 2019, the agency also conducted an analysis of the possible interaction between programmable CSF shunt valves and implanted hearing devices, again determining that magnets in the devices may affect valve settings in the shunt systems.
FDA recommends keeping products that contain magnets two or more inches away from the location of magnetic externally programmable CSF shunt valves. Patients are advised to use the ear opposite the shunt for devices such as cell phones and earbuds.
Healthcare providers are advised to consider placing a programmable CSF shunt valve on the contralateral side of a cochlear implant or implantable bone conduction hearing device. For patients requiring bilateral hearing implants, which use magnets and a programmable CSF shunt, the implanting physician should position the shunt valve and the ipsilateral hearing implant at a maximum distance from each other.
If a magnetic interaction inadvertently changes a shunt’s valve settings, patients may experience symptoms that initially include altered mental status, headache, lethargy, irritability, vomiting, change in vision and difficulty walking. Symptoms may become more serious if unchecked.