Contrast Dyes for MRI in Multiple Sclerosis

Magnetic resonance imaging (MRI) is the gold standard test for diagnosing and monitoring the progression of multiple sclerosis (MS). Some types of MRI require the use of a substance called gadolinium-based contrast dye (GBCD). This substance, which is administered through a vein during the test, causes MS lesions to "light up." This can be helpful in evaluating MS, but it's important to know that the dye has certain side effects and risks.

Gadolinium is a chemical compound that when injected into the bloodstream normally can't get past the blood-brain barrier—a layer of membranes and cell processes that prevents substances in blood from entering the brain or spinal cord.

The blood-brain barrier is largely impermeable. However, under certain circumstances, such as active inflammation within the brain or spinal cord that occurs during an MS relapse, the barrier is disrupted.

When this happens, gadolinium can enter the brain or spinal cord and leak into an MS lesion, causing it to show up as a highlighted spot on an MRI. 

Most of the side effects of gadolinium-based contrasts (GBCDs) are mild, including:

• Headache
• Nausea
• Dizziness
• A cold sensation when injected

Of more concern is the possibility that the contrast material won't be completely eliminated from the body.

The FDA published this warning even though it wasn't clear if the retention of GBCDs would be harmful over time. More recent research suggests that any build-up of gadolinium is dose-dependent—that is, the more times a person receives the dye, the more brain deposits they're likely to have.

The same study concluded that there is no link between the brain deposition of gadolinium-based contrast agents and a person's kidney function, age, gender, or the period of time between their contrast exposure (their last MRI) and death.

It's also important to note that contrast material is even more likely to be deposited in bone than in brain tissue, although the implications of this aren't yet clear.

Rarely, certain types of gadolinium contrast cause a serious disease called nephrogenic systemic fibrosis in people with significant kidney dysfunction. This condition, which causes tightening of the skin and damage to internal organs, is most likely to occur in people with MS who also have kidney dysfunction.

Although rare, some people have a mild allergic reaction to gadolinium contrast. The main symptom is itchy skin.

MRI imaging uses magnets and radio waves. For that reason, pacemakers, artificial bones or joints, and even IUDs can cause problems, as the MRI uses very strong magnets to create images.

In addition, MRI machines may be problematic for people with claustrophobia. To minimize this risk, imaging centers increasingly use open MRI equipment.

If you are undergoing an MRI, be sure to tell your doctor and the MRI technologist if you have any metal implants, claustrophobia, allergies, or kidney problems. They will be able to tell you what is and what is not safe and how to best proceed.

MRI technology makes it possible to view the structures of the central nervous system (the brain, spinal cord, and optic nerve) non-invasively—that is, without the need for surgery. They can be done without contrast dye, but in many cases of MS, gadolinium greatly improves the information a scan provides, making it much easier to identify and quantify lesions.

That being said, if your doctor doesn't suspect active inflammation and is simply monitoring the periodic progression of your disease, contrast is generally not be needed and you will not need to undergo the small risks that the dye presents.