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Monday, November 4, 2013
New 3D Imaging Technique Shows Myelin Damage, Helps Diagnose MS
Written by Jeri Burtchell
PET scanning using a new marker that attaches to myelin may be the next "gold standard" diagnostic tool for multiple sclerosis.
Waiting months or even years for a definitive diagnosis of multiple sclerosis (MS) may soon be a thing of the past. Researchers at the Case Western Reserve University School of Medicine have developed a breakthrough method of detecting myelin damage using positron emission tomography, or PET scanning.
MS is an autoimmune disease that destroys the fatty insulation, called myelin, that covers nerves in the brain and spinal cord, resulting in a vast array of symptoms. The many variations—and combinations—of MS symptoms make diagnosis difficult.
Until now, testing for MS meant ruling out every other possibility. According to the National Multiple Sclerosis Society (NMSS), treatment with an FDA-approved disease modifying drug “should be considered as soon as possible following a definite diagnosis of MS" in order to delay the disease progression. For those with a delayed diagnosis, however, treatment must wait.
“Our discovery brings new hope to clinicians who may be able to make an accurate diagnosis and prognosis in as little as a few hours, compared to months or even years,” said Yanming Wang, Ph.D., senior author of the study and an associate professor of radiology at Case Western, in a press release. “...it is particularly difficult to directly detect myelin damage in the spinal cord; this is the first time we have been able to image its function at the molecular level.”
The technique uses a new marker to detect and measure myelin changes. When the marker, known as MeDAS, is given to the patient through an IV injection, it can easily reach the brain and spinal cord and bind to the patient's myelin sheaths. The PET scanner then visualizes where the marker has accumulated in the patient's body.
“The concentration of MeDAS is high in the region where myelin remains intact,” Wang told Healthline, and low where myelin has been damaged. By using the MeDAS marker, “the integrity of myelin along the whole spinal cord can be examined and monitored over time.”
A New Gold Standard
A PET scanner is a large, ring-shaped device with a bed that slides into the center. After being given an injection containing positively-charged particles, or positrons—in this case, MeDAS—the patient is scanned while lying on the bed. The machine detects the MeDAS, which lights up on a computer monitor, creating the 3D image. Areas of demyelination will appear as dark areas on the scan.
For patients with MS who are used to undergoing magnetic resonance imaging (MRI) scans, results that “light up like a Christmas tree”—indicating high disease activity—are undesirable. But having a PET scan using the MeDAS marker lighting up is a good thing because it means more myelin is present.
“Only trace amounts of MeDAS will be needed for the scan,” said Wang, “so it is safe for all people. No other medical conditions or prescription drugs exclude a person for using the technique.”
The PET scan typically takes between 60 and 90 minutes. "The data is then interpreted by a neuroradiologist who will read the scans," said Wang. “It normally requires specialized training to read them.”
The MeDAS will be metabolized and excreted out of the patient's body soon after the PET scan is completed, and there is no chance of an allergic reaction to the organic molecule. “There is no danger from repeated exposure to radiation in this type of PET scan due to the fact that the half-life of MeDAS is only 20 minutes,” Wang added.
Using this new molecular marker to highlight existing myelin sheaths will make areas of missing myelin obvious. This type of PET scan could soon replace MRIs for monitoring a patient’s disease progression during routine annual exams.
Traditionally, the MRI has been the gold standard for tracking disease activity in MS. But MRI is not selective and only shows the shadows of inconsistencies. Many other conditions, such as cancerous tumors, can mimic MS scarring on MRI images, so further testing is often required to rule them out.
Researchers are excited by their breakthrough and what it means for the future of MS. “This can become a standard diagnostic tool to monitor disease progression over time, verify a suspected relapse, and identify individuals at risk, who have family history of MS,” said Wang.