Biomedical implants are becoming more and more common in today’s world of modern medicine. For instance, roughly one-million knee replacement surgeries were done in the U.S. last year. With these numbers, it’s not a surprise that allergic reactions to the implants is also increasing. Diagnostic features of metal hypersensitivity to an implant include: rash developing in the skin overlying the implant, generalized skin rash beginning weeks to months after the implant, unexplained pain and/or failure of the implant, positive patch test to the metal used in the implant and complete resolution of symptoms after removal/replacement of the offending implant.
The most common causes of metal hypersensitive reactions are orthopedic devices. Next most common are dental-related metals. Much less common are vascular stents, cardiac pacemakers and gynecologic implants, such as intrauterine devices (IUDs). The metal type causing the most problems is stainless steel — which contains nickel, cobalt and chromium – all known potential allergens. Less troublesome are titanium alloys and zirconium.
The most common allergic symptom seen with cardiovascular stents is rapid re-stenosis of the “stented” artery. In the case of pacemakers/internal defibrillators, it is a rash in the skin overlying the device. Unfortunately, there are no standardized test kits for metal testing. Currently, skin-patch testing with a small piece of the implant metal, and a blood test to see if white blood cells react are in use, but results can vary from lab to lab. Most vexing is the fact that the allergy can develop after the implant. However, any implant candidates with previous allergic issues with the proposed metal should undergo pre-testing — including reactions to piercings, tattoo ink, jewelry or metal snaps.