First Direct Measurement Of Spinal Cord Myelin In MS

Scientists at the Case Western Reserve University School of Medicine have developed a new imaging tool to examine myelin damage caused by multiple sclerosis (MS). They believe their novel technique will help physicians diagnose patients earlier, monitor the disease's progression, and evaluate therapy efficacy.

The researchers have come up with a molecular probe detectable by positron emission tomography (PET) imaging. The new molecular marker, MeDAS, reportedly offers the first noninvasive visualization of myelin integrity of the entire spinal cord at the same time, as published today in an article ("Longitudinal Positron Emission Tomography Imaging for Monitoring Myelin Repair in the Spinal Cord") in the Annals of Neurology.

"MeDAS selectively stains myelin in the spinal cord and brain. Neuroinflammation did not affect MeDAS uptake in the brain as long as the myelin sheaths remained intact," wrote the investigators. "Longitudinal PET studies in LPC and EAE rat models demonstrate that MeDAS uptake changes correlate with associated myelin loss in the spinal cord."

According to Yanming Wang, Ph.D., senior author of the study and associate professor of radiology at Case Western Reserve University School of Medicine, although MS originates in the immune system, the damage takes place in the myelin structure of the central nervous system.

"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 Dr. Wang. "Because of its shape and size, 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."

In addition to its role in monitoring the effects of myelin-repair drugs currently under development, the new imaging tool offers a real-time quantitative clinical diagnosis of MS. A long lag exists between the onset of disease, physical symptoms in the patient, and diagnosis via behavioral testing and magnetic resonance imaging (MRI). The lesions, or plaques, as detected by a MRI in the brain and spinal cord are not myelin specific and thus poorly associated with a patient's disease severity or progression. There is an urgent need to find a new imaging marker that correlates with a patient's pathology.

The MeDAS molecular probe works like a homing device. Injected into the body intravenously, it is programmed to seek out and bind only to myelin in the central nervous system. A positron-emitting radioisotope label on the molecule allows a PET scanner to detect the targets and quantify their intensity and location. The data can then be reconstructed into an image.

"This discovery has open the door to develop new drugs that can truly restore nerve function, not just modify the symptoms," noted Robert Miller, Ph.D., co-author on the study and vp for research for Case Western Reserve and the Allen C. Holmes Professor of Neurological Diseases at the School of Medicine. "A cure for MS requires both repairing myelin and a tool to measure the mechanism."

"The studies described above represent a unique PET approach to monitoring myelin damage and repair in the spinal cord without requiring invasive surgeries or biopsies," concluded the scientists in the Annals of Neurology article. "Use of this newly developed myelin imaging technique to serially quantify local myelination should enable more efficient development of therapeutics directly focused on facilitating remyelination and the protection or regeneration of neural tissue."

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