Veterinary Neurology and Neurosurgery

Intervertebral disc disease (IVDD) is the most frequently encountered spinal disorder in dogs and can also occur in cats. The intervertebral discs are fibrocartilaginous structures located between most vertebrae, with the exception of the joint between C1 and C2. They provide support and flexibility to the spine while also helping to absorb mechanical forces. When these discs degenerate, their normal structure and function are progressively altered, making them more prone to disc herniation and spinal cord compression.

IVDD develops as a consequence of degenerative changes within the intervertebral discs. In some dogs, particularly those classified as chondrodystrophic, these changes can begin at a relatively young age. The centre of a healthy disc has a well-hydrated, jelly-like consistency; with degeneration and dehydration, it becomes more like a gritty paste. This change alters its function, decreasing its ability to be flexible and absorb shock, and makes it more likely to result in disc bulging or herniation.

Chondrodystrophic breeds have characteristically shortened limbs in proportion to their body length. Dachshunds, Beagles and many Terrier breeds are common examples. These dogs are predisposed to developing early degenerative changes within their intervertebral discs, increasing the likelihood of subsequent disc-related disease.

Dogs and cats with IVDD may initially develop pain localised to the spine, either in the neck or back. Neurological dysfunction can subsequently develop, ranging from mild weakness through to complete paralysis. In some patients, sudden paralysis may be the first obvious indication of a spinal problem.

Because the spinal cord carries nerve pathways between the brain and the limbs and organs, the location of the disc lesion determines which parts of the body are affected. For example, disease affecting the lower back may result in hindlimb weakness or paralysis and may interfere with normal bladder function. A disc problem within the cervical spine can affect all four limbs and may result in weakness or paralysis.

Pain is commonly one of the earliest clinical signs. Affected animals may adopt an abnormal or hunched posture, tremble, pant, become reluctant to move, or have difficulty jumping onto furniture or climbing stairs. As the condition progresses, animals may develop an unsteady gait, reduced limb coordination, weakness, ataxia or paralysis. Severe spinal cord injury can also result in impaired bladder emptying and loss of sensation in the limbs.

Spinal cord disease should be considered an emergency. Veterinary assessment by a Specialist Surgeon should be sought promptly following the development of neurological or spinal pain signs, as delays in treatment may negatively affect the prognosis.

IVDD may be suspected from the clinical examination and the patient’s breed and history, but imaging is required to establish the diagnosis and determine the exact location and severity of the lesion. Standard spinal radiographs can demonstrate changes associated with disc degeneration, but they generally do not provide sufficient information about the spinal cord or the precise location of compression to allow appropriate surgical planning.

Advanced diagnostic imaging is therefore required for definitive assessment. Depending on the individual patient, myelography, computed tomography (CT) or magnetic resonance imaging (MRI) may be recommended. The most appropriate imaging technique will be selected by the surgeon according to the clinical presentation and suspected location of the lesion.

Advanced imaging provides considerably more information than routine radiographs and allows the BVRS team to identify the site of spinal cord compression and formulate an appropriate treatment plan. Because the patient must remain completely still during these procedures, deep sedation or general anaesthesia is required. Without advanced imaging, an accurate diagnosis and appropriate treatment plan cannot reliably be established.

A number of other diseases can produce clinical signs that resemble IVDD. These include inflammatory conditions such as meningitis, infection involving the vertebrae or intervertebral discs, spinal tumours or other cancers, vascular events involving blood clots (spinal stroke) or cartilage clots (FCE), traumatic spinal injury and paralysis caused by tick envenomation.

Because these conditions can have very similar clinical presentations, diagnostic imaging such as myelography, CT or MRI is often necessary to distinguish between them and identify the underlying cause.