The back, from the neck to the tip of the tail, is made up of numerous small bones called vertebrae. These vertebrae are connected together by intervertebral disks. These disks are a pad of fibrous tissue with a central gel like substance which act as a shock absorber, and also allows movement of the spine.
Within the bony vertebrae is a central tunnel, through which the spinal cord runs to protects it from damage. Between the vertebrae the spinal cord runs over the top of the disks. The spinal cord contains lots of bundles of nerves that relay messages back and forward to the rest of the body from the brain.
With age, and wear and tear, the disks start to degenerate. The outer fibrous portion may start to fray and weaken so that the central gel like part of the disk can protrude upwards, putting pressure on the spinal cord, or nerve roots leaving the spinal cord. This can either happen acutely, where the disk can suddenly rupture and hit the spinal cord with the force of a gunshot, or more slowly, causing small amounts of pressure on the spinal cord. The acute form is seen more commonly in certain breeds of dogs with a genetic weakness to their disks, and can happen at a young age. These include Dachshunds, Corgis, Basset Hounds, Shih Tzu’s and Beagles. Disk protrusion can happen after an episode of known trauma, such as jumping down, but can also happen spontaneously as the disk is already weakened.
Symptoms depend on the severity of the disk protrusion and the force that it hits the spinal cord. It also depends on the location of the disk injury. Initially it can cause intense pain.
Your vet may suspect a disk injury based on clinical signs and physical examination of your dog – especially if he/she is one of the predisposed breeds eg Dachshund. Your vet will try to determine the location of the pain and also do a full neurological exam to check for signs of spinal damage. Further diagnostic testing may then be warranted. Initially your vet may need to take an x-ray of your dog’s spine. This may be useful to rule out other causes of back pain or spinal injury, such as a fracture, tumour or possible infection. Unfortunately a plain x-ray is often not very helpful to check for a disk protrusion, as the spinal cord and the disk do not show up (only bone can be seen). Sometime though, the disk space may be narrowed as the disk material has moved upwards into the spinal canal, or there may be evidence of calcification in a damaged disk. However, if it is important to find out which disk is affected, then more specialised diagnostic techniques are required. These need to be performed at referral centres by veterinary specialists and include Myelography (radiographic dye injected around spinal cord which highlights areas of spinal cord compression) and CAT/CT/MRI scans.
Medical (non-surgical) treatment may be the best option if your dog is only showing mild symptoms. Anti-inflammatory drugs are often used to reduce swelling around the spinal cord or nerve roots and they also help to reduce pain. If additional pain relief is needed then opiates drugs such as codeine/tramol may be required. It is also really important to rest your dog which helps to decrease inflammation and prevent the disk protruding any further. Your dog may require strict cage confinement for up to 6 weeks.
If your dog has recurrent episodes of back pain, severe pain or signs of spinal cord damage, then surgery may be the best option. With severe signs your dog will need surgery ASAP to prevent permanent damage to the spinal cord. This requires referral to a specialist surgeon. After determining the disk involved, the surgeon will either remove the degenerate centre of the disk (fenestration) or perform decompressive surgery (laminectomy). Laminectomies involve removing a portion of the vertebrae to expose the spinal canal, so that the disk material can be removed. Strict rest with cage confinement is imperative to allow healing to occur.
With mild episodes of disk disease the prognosis for your dog with medication and rest is excellent. However it is important to realise that the chance of the disease recurring is around 50%, especially if your dog is allowed to jump freely and if he/she is obese.
Dogs that have had surgery also have a good chance of recovery within 1-2 months and with strict rest. However if your dog has complete paralysis for a number of days or has no pain sensation then the prognosis for recovery is very poor.