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This article addresses treatment guidance associated with performing TMS on patients with metallic implants, both medical and aesthetic.
The theoretical concerns of conducting TMS with an implanted or non-removable device present are heating of the implanted device if it is made of highly conductive material, mechanical movement of an unanchored implanted device if it is made from a highly ferromagnetic material, demagnetization of implanted permanent magnets, and induction of a current in the wires or electrodes of the implanted device.
Based on the magnetic fields created by TMS coils, the previously published FDA guidance on which manufacturers based their instructions for use documents is likely overly conservative and limits the availability of TMS for patients with implanted devices.
General rules of thumb:
• Anything MRI safe or conditional is TMS safe, including tattoos and jewelry.
• Very conservative guidance is to avoid placing ferromagnetic material within 10 cm of the coil
• Mechanical movement of an implanted device is not a problem
• Heating of non-ferromagnetic material is not a problem
• Even closer than 10 cm, anything anchored such as a screw or plate will not move under the influence of TMS
• Hearing aids should be removed during TMS for hearing protection
• No damage has been seen to implanted vagal and hypoglossal nerve stimulators with TMS
• No damage has been seen to cochlear implants or ventriculoperitoneal shunts with TMS, although manufacturers offer specific MRI guidance
• TMS in patients with deep brain stimulators should be done only if there are justifiable scientific or medical reasons. In such case, the TMS coil should be operated away from the electrode leads
• For patients that have an unknown implant in the skull, it may be useful to use a handheld ferromagnetic detector