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Case Study - Grade 3 Wobbler

5-year-old Thoroughbred presents for increasing ataxia and falling over.

This case study was written for Illawarra Equine Centre by Georgia Cain, vet student. at University of Sydney in her final year Doctor of Veterinary Medicine | University of Sydney 

History

On 22/07/22 a 5-year-old Thoroughbred gelding was found recumbent in his stall. The trainer was able to get the horse up overnight and he remained ambulatory until consultation the next morning. The trainer reported the horse had a history of clumsiness and stumbling behind. On presentation he had very poor proprioception and a weak tail pull, there was high suspicion this horse has Grade 3/5 Wobbler Syndrome (Cervical Vertebrae Stenotic Myelopathy). It was recommended at the time to cease work and not to put a rider back on this horse at risk of catastrophic injury to both. The possibility of euthanasia was discussed with the owner as was spelling the horse at a suitable property.

 

Seven days after the initial presentation on the 30/07/22, this horse became recumbent again. On examination the horse was laterally recumbent with the ability to rise into sternal recumbency for a period of a few seconds. Attempts to rise were unsuccessful and there was generalised muscle fasciculations, there was a rapid progression of the Wobbler Syndrome, re-classifying the ataxia as a Grade 5/5.  The horse was kept sedated for a period of time, whilst the insurance company was consulted.  Humane euthanasia was performed on 31/07/22 and the horse was sent for a post-mortem with histopathology of the spinal cord to satisfy the requirements of a diagnosis for insurance purposes.

Wobbler Syndrome: Cervical Vertebral Stenotic Myelopathy

Cervical Vertebral Stenotic Myelopathy (CSVM) or Wobbler Syndrome, is neurological conditions characterised by of malformations and malarticulation of the cervical vertebrae, which cause stenosis of the vertebral canal and compression of the spinal cord. Which causes the deformed or unstable vertebrae press against the spinal cord, resulting in proprioceptive deficits. When mild, CSVM results in hind limb ataxia, however as the degree of compression increases, the signs progress to spasticity and paresis, as the deep motor neuron pathways are affected. It is referred to as "wobbler" syndrome, as the horse may seem wobbly when walking or exercising. These horses suffer from "ataxia" from a proprioceptive deficit or loss of sense where their feet are placed.

CVSM primarily manifests as general incoordination or stiffness when the horse moves. Affected patients may trip, appear to lurch at the canter, have difficulty halting smoothly, swing out or collide their limbs while turning and walking up and down hills can also be difficult for the horse. Neurological signs may be noted secondary to behavioural changes such as, changes under saddle; bucking, bolting, rearing & stopping at fences as well as resistance to working in one direction or reluctance to work within a frame. The trainer may notice an occasional stumble, or the horse might have fallen under circumstances where it was not expected. Some horses have difficulty traversing hills but work well in other situations.

The spinal cord compression can present itself as a dynamic or static stenosis of the cervical canal. In a dynamic stenosis, compression only occurs when the horse bends or extends its neck and affects most commonly the intervertebral spaces between the third and fourth cervical vertebra (C3-C4) and C4-C5 in young animals (yearlings). On the other hand, static stenosis occurs regardless of the position of the neck and occurs most commonly between C5-C6 and C6-C7 in older animals. The aetiology of this condition has been linked to osteochondrosis (degeneration of the growth centres), nutritional factors and mineral imbalances. There is no evidence that this condition is heredity.

mouth. This is typical of a choke reflux caused by mixed saliva and feed.

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Diagnosing Wobbler Syndrome in your horse:

 

A presumptive diagnosis is obtained by a combination of a detailed history from owners and trainers, breed and age of the horse and an in-depth neurological exam performed by your vet. The neurological exam should include but not be limited to:

  • signs of in-coordination, and weakness while moving in hand at the walk and trot, both in a straight line and circling, Serpentines, walking with the head elevated, walking tail pull, tight circles in both directions, backing up, walking up and down hills with the head in a neutral and elevated positions and nose to flank & nose to ground examinations

 

The ataxia should be graded accordingly: 

Grade of Ataxia        Clinical Signs

Grade 0                     Normal

Grade 1                     Minimal neurological deficits

                                  Require proprioceptive/ manipulative tests: crossing legs, tail sways, tight circles,                                                                      blindfolding and backing in order to demonstrate clinical signs of syndrome

Grade 2                     Mild abnormal gait seen at the walk (may appear to walk like a sedated horse)

                                  More obvious response to proprioceptive/ manipulative tests

                                  Patients may perform successfully, however may have trouble with lead changes, going down hills at                                        gates faster than a walk, stumble, require a lot of stimulation to maintain propulsion, knuckle over when                                    stopping, bunny hopping behind when cantering or drag hind toes at the trot

Grade 3                     Easy to see at the walk, very obvious at the canter but do not fall over

Grade 4                     Very ataxic, fall especially in tight circles or backing. Usually refuse to move faster than a walk

Grade 5                     Recumbent, may not move into sternal recumbency even with encouragement

To diagnose CSVM, radiographic myelograms under general anaesthesia of the cervical (neck) vertebrae are needed to reveal some malformations/ malarticulation the cervical vertebrae which lead to the clinical signs of ataxia and paresis. These malformed or compressed vertebrae press against the spinal cord and interfere with messages being sent by the brain. Interference with normal nerve transmission from the brain to the legs then leads to noticeable lack of coordination (ataxia).

Are there different types of CVSM?

 

Yes, there are three types of CVSM (Wobbler syndrome), these can be classified by your veterinarian through diagnostic procedures such as radiographs, myelograms, and/ or computerised tomography (CT) of the cervical spine (neck).

 

Type 1: most commonly associated with the second and third cervical vertebrae and usually present at birth

Type 2: most commonly associated with the upper and middle cervical vertebrae and mostly occur in sucklings and weanlings

Type 3: most commonly associated with C5, C6 & C7 and can include the first thoracic vertebrae, these lesions mostly occur in older horses but may be seen in young horses

Can my horses wobbler grade change?

 

Yes, horses can deteriorate over time or very rapidly. A wobbler that is not treated may deteriorate neurologically, occasionally to the point of injuring itself or others, especially when struggling to rise. In the short term, medical treatment with stall rest may provide some benefit for a wobbler that is subtly affected. In the long term, however, frequently the animal will relapse when allowed unrestricted exercise or when placed in training.

Grade 3 Wobbler grade change.png

Prognosis

 

Factors that influence prognosis include age of the horse, severity of neurologic deficits, duration of neurologic signs, and owner expectations for performance. Most horses with CVSM do not have life-threatening ataxia, although some horses become unable to rise or demonstrate such severe incoordination that safety concerns warrant euthanasia. Without treatment, prognosis for substantial improvement in neurologic function is generally poor as the underlying malformation, instability, or bony proliferation will continue to damage the spinal cord. Additionally, sudden deterioration in neurologic status can occur following trauma, as a horse with a narrowed spinal canal has little ability to compensate or avoid further injury to the cord when trauma occurs.

 

There are medical and surgical interventions that may be considered depending on the grading of the ataxia seen on clinical examination. Your veterinarian will be able to guide you through treatment options if Wobbler syndrome has been diagnosed. Humane euthanasia is a reasonable consideration, as this syndrome can be unsafe for both the horse and rider.

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