What's Behind Wobbler Syndrome?

What's Behind Wobbler Syndrome?

Traditionally, veterinarians have diagnosed wobbler syndrome via standing cervical radiographs and/or a myelogram (seen here) in association with clinical history and neurologic deficits on physical exam.

Photo: University of Kentucky Gluck Equine Research Center

Although researchers have been studying wobbler syndrome for years, they still have questions about the condition's etiology and pathogenesis.

At the 2013 University of Kentucky (UK) Equine Showcase, held Jan. 18 in Lexington, Ky., Jennifer Janes, DVM, a PhD candidate at the UK Gluck Equine Research Center, reviewed what we know about wobbler syndrome and what questions remain, in addition to sharing some research results that could help veterinarians diagnose the disease.

What We Know

Wobbler syndrome is a colloquial term used to describe neurologic disease resulting from spinal cord compression in a horse's neck, said Janes. Several terms have been—and still are—used to describe the disease, including cervical vertebral malformation, cervical stenotic myelopathy, cervical vertebral instability, and cervical static stenosis. Researchers have found that Thoroughbreds, Tennessee Walking Horses, Warmbloods, and Quarter Horse-type animals appear more predisposed to developing the disease, and colts are diagnosed more than fillies, Janes said. The average age of disease onset ranges from 6 months to 7 years, she noted. The most common clinical signs observed in affected horses include ataxia (incoordination, more common in the hind limb than the forelimb), toe dragging, moving the hind limbs in a circular pattern, overreaching with hind limbs, and a base-wide stance.

Janes explained that a number of causes have been implicated for the disease, including:

  • Genetics;
  • Rapid growth;
  • High carbohydrate diets;
  • Decreased copper and increased zinc levels in diets; and
  • Trauma.

Traditionally, veterinarians have diagnosed wobbler syndrome via standing cervical radiographs (X rays) and/or a myelogram (a special X ray of the spinal canal that reveals spinal cord compression) 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 from the side.

In 2011 Janes evaluated MRI for identifying spinal cord compression and found it very effective. Additionally, she said, measuring the spinal canal area allowed for a more accurate identification of compression sites when compared to radiographs.

The drawback of this method, Janes noted, is that currently, MRI machines are not large enough to accommodate a live horse's head and neck; her trials were carried out post-mortem. She said, however, that MRI machines are gradually getting larger and the technology is improving such that the ability to image the entire neck of a live horse in a clinical setting should ultimately be possible.

Once veterinarians reach a diagnosis, they're able to start treating affected horses either conservatively or surgically, she said.

The conservative treatment approach consists of making dietary changes to avoid excess weight gain to ensure a balanced calcium/phosphorus ratio, feeding grass hay, supplementing copper and zinc, and limiting exercise to reduce the likelihood of trauma.

Surgical treatment typically consists of fusing the affected vertebrae together using a metal implement called a "basket" in a surgical procedure called cervical stabilization. This fusion prevents the vertebrae from compressing the spinal cord.

Current Research

Next, Janes discussed two research projects she's working on to further understand wobbler syndrome's etiology and pathogenesis. She's currently evaluating cervical bone structure and pathology in affected horses compared to healthy horses, and she's also investigating the possible role of genetics.

For the former project, Janes and colleagues are using a combination of a gross evaluation, histology (microscopic tissue examination), MRI, and micro-CT (microtomography, which uses X ray images to create 3D virtual models allowing for evaluation of the bone microarchitecture) to examine wobbler horses' bone pathology. Janes explained that she's able to compare findings on the gross examination with those identified on MRI and micro-CT, allowing for a more in-depth look at these horses' vertebrae structure.

The ultimate goal of this research, she said, is to further understand pathology in the cervical column that could lead to improved treatment and management options for wobbler horses.

In the latter project, Janes and colleagues are using DNA-based tools for analyzing the equine genome to try to identify if wobbler syndrome has genetic determinants. Anecdotal reports suggest genetics could play a role in disease development. Although a breeding study effectively ruled out a simple mode of genetic transmission, a more complex mode of inheritance is still possible. Using the genome, Janes is performing a genome-wide association study to evaluate the genotypes of SNPs, or single nucleotide polymorphisms (a common type of genetic variant), that could identify regions of genetic interest for wobbler syndrome.

Take-Home Message

"Wobbler syndrome remains an important neurologic disease of the horse," Janes concluded. "Current diagnostic imaging and molecular techniques are now available to reinvestigate longstanding unanswered questions regarding etiology and pathogenesis."

About the Author

Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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