MRI to Detect Wobbler Syndrome? (AAEP 2011)

In most cases--if not all--a clearer picture is better. One would be hard-pressed to find a person who would walk into a store and ask for a television with a fuzzy picture. So when it comes to disease diagnosis, such as that for cervical stenotic myelopathy (CSM, also known as cervical vertebral stenotic myelopathy), wouldn't a clearer picture that reveals more information be beneficial? One University of Kentucky researcher thinks so.

During a presentation at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas, Jennifer Janes, DVM, presented a study supporting the use of magnetic resonance imaging (MRI) in diagnosing spinal cord compression and CSM (more commonly known as wobbler syndrome).

Spinal cord compression due to misaligned or malformed vertebrae damages spinal cord nerves responsible for the horse being able to sense the position of his limbs. This leads to clumsiness and incoordination, especially in the hind limbs, and the distinctive "wobble."

Traditionally, cervical stenotic myelopathy has been diagnosed via standing cervical radiographs and/or a myelogram in association with clinical history and neurologic deficits on physical exam. But while standing cervical radiographs and myelography can detect narrowing of the vertebral canal, they limit visualization of the spinal canal to two dimensions from the side.

Conversely, MRI allows for spinal canal assessment in three dimensions, as well as an evaluation of both soft tissue and bone structures, Janes noted.

To compare the efficacy of current diagnostic imaging techniques with the potential effectiveness of MRI in confirming spinal cord compression, Janes et al. studied 20 Thoroughbred horses with CSM ranging in age from 6 months to about 4 years old, and nine control horses ranging in age from 6 months to about 5½ years old.

All of the horses underwent a neurologic examination and standing cervical radiographs. The researchers calculated sagittal (i.e., space from front to back) ratios from the third to seventh cervical vertebrae (C3 to C7) on the radiographs. Postmortem, they scanned each horse's intact cervical column using an MRI unit. Finally, the team performed a histologic examination of each spinal cord to definitively localize compression sites.

After reviewing the results, Janes concluded that "MRI, with its ability to visualize the vertebral anatomy in three dimensions, allows for valuable additional measurements of the vertebral canal. For example, vertebral canal area and circumference among other parameters can be evaluated at each cervical vertebral joint. Specifically, canal area was found to more accurately identify sites of compression in CSM horses."

Janes noted, of course, that today's MRI machines are not yet large enough to evaluate the entire length of cervical columns in live adult horses (antemortem). "However, when this technical issue is resolved, the ability to image vertebrae in multiple axes will substantially enhance evaluation of CSM patients," she concluded.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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