Skin and Bones: The two most common sites for Gd Retention/Deposition
Much has been written, including by myself with co-authors of Gd being deposited in the brain following GBCA administrations. This deposition has come to radiologist attention because it is visible on MR images. This has largely been observed with linear agents, and is visually apparent after about 5 doses. Although it has been greatly emphasized, as I have stated in earlier blogs, the amount of Gd deposited in the brain is far less than that in the bones or the skin. Ken Maravila and his team have shown the concentration of Gd in bones to be something like 20 times that in the brain. When you then factor in the difference in overall mass between these organ systems, the actual difference in amount of Gd is probably in the range of 2,000 times greater amount of Gd located in bone, and probably about the same amount greater in skin, than in the brain. So when we talk about Gd deposition we really should be focusing on skin and bones.
The major explanation for Gd being in such high amounts in the bone, is that Gd substitutes in for Ca in bone construction. Interesting though this explanation should not account for why intact GBCA chelates go to bone, as we would expect with the macrocyclic agents: prohance, gadavist, and dotarem, that they should be remaining intact. I will discuss the curious case of intact macrocyclics causing things in a future blog.
Skin deposition has been perhaps the major focus of most animal studies with GBCAs, and certainly has also been the major focus with NSF. The exact mechanism of why GBCAs go so avidly to skin, in my mind, has not been elucidated. It is a large organ system, and including skin substrate, probably overall the largest capillary network. Furthermore in dependent locations, and in the setting of poor blood flow, interstitial fluid (hence where Gd would be) tends to pool in these locations. So this all makes sense. Probably a further explanation, and along the idea of Gd substituting for Ca in bone, is that Gd also substitutes for sodium (Na) in sweat. In an earlier blog I described this substitution (Gd for Na) in tears, as an explanation for dry eyes in GDD sufferers. So Gd substituting for Na likely is a partial explanation for its presence in skin.
This concept provides both a rationale and a warning for using saunas to extract Gd from the body, by 'sweating it out'. This likely is correct that this happens, what is not certain as yet is how much Gd is sweated out. A cautionary note though is that this may cause more Gd to relocate to the skin from elsewhere in the body, which could result in more skin symptomatology (such as burning). An obvious way to counteract this, prior to the sauna and for a few hours afterwards, is to have a very high oral water intake and preferably as alkaline water. Also to shower immediately after the sauna to remove any Gd on the skin and possibly in the most superficial layer of the epidermis and superficial sweat ducts. Mildly hot shower with a gentle soap.