Canine intervertebral disc disease: how much do we really know?

7 March 2023

In 2019, Paul Freeman received a BSAVA PetSavers grant of £13,000 (including £5,000 donated by The Debs Foundation) for a project entitled Recovery of ambulation in medically-managed non-ambulatory Dachshund dogs with thoracolumbar intervertebral disc herniation at the University of Cambridge Queen’s Veterinary School Hospital with Sam Khan.

Canine thoracolumbar intervertebral disc extrusion (IVDE) is a common reason for presentation in clinical practice. Any breed of dog can be affected but it most commonly occurs in chondrodystrophic breeds such as Dachshunds which have an estimated lifetime prevalence of approximately 20%. Clinical signs can range from back pain alone to paraplegia with absent pain sensation in the hindlimbs and tail and even death from progressive ascending-descending myelomalacia.

Clinical signs are caused by extrusion of degenerate and calcified nucleus pulposus from within an affected intervertebral disc impacting the spinal cord and causing a mixture of contusive and compressive injury to the spinal cord. It seems logical that where there is a compressive lesion, treatment should aim to remove it, especially when there are currently no treatments which specifically target the contusive injury; this is the rationale behind decompressive surgery. Since its introduction over 50 years ago, surgical decompression by various methods has been shown to be successful in numerous case series, and this success has led to a widespread perception that dogs who suffer a significant IVDE, especially those who are so severely affected that they are rendered non-ambulatory, require decompressive surgery in order to recover. It is, however, also well known that some affected dogs can recover without decompressive surgery, i.e. with medical or conservative management. In 2017, a review by Freeman and Jeffery1 demonstrated that the recovery rates of dogs managed by non-decompressive methods were similar to those following surgical management, except in those dogs who lose deep pain perception (DPP) in the pelvic limbs.

There is, however, a relative lack of data to support conservative management and, to date, there have been no formal clinical trials comparing medical and surgical management. A review in 2017 by Langerhuus and Miles2 showed improved outcomes in non-ambulatory dogs treated surgically compared to medically treated, but also called for more robust clinical trials to confirm these findings. For vets in general practice as well as specialist neurologists, this lack of equipoise regarding the chances of successful outcome with medical versus surgical management means there is often a tendency to recommend surgical treatment, and a reluctance to support conservative management. When combined with the high financial costs of cross-sectional imaging and surgery, this means that some dogs are likely being euthanased when their owners are unable to afford surgical treatment. It also means that dogs may undergo surgical treatment when they could have recovered perhaps just as well with medical management.

What are the aims of the current research?

Given the lack of equipoise regarding the evidence and likelihood of successful outcome with surgical versus medical management, a direct comparison in the form of a randomized clinical trial is not currently possible. Instead, our aim is to provide further information about medical management in order to facilitate evidence based clinical decision making in thoracolumbar IVDE.
The specific aims are as follows:

  • To document the natural history of thoracolumbar IVDE through repeated neurological examination and MRI (example image seen in Figure 1)
  • To document the change in nature and severity of compression seen on MRI over time and how this is related to recovery
  • To report the proportion of dogs who recover and time to ambulation of those dogs rendered non-ambulatory but treated non-surgically
  • To assess various physical examination, neurological examination, MRI findings and management factors for their impact on prognosis and time to ambulation
  • To begin to determine who will benefit most from surgical intervention.

Figure 1. Sagittal T2W MRI image showing a severely compressive intervertebral disc extrusion

What have we learned so far?

Data collection is still ongoing and so statistical testing has not been undertaken; however, our results so far suggest that:

  1. Many dogs who are managed medically will recover, including those who lose DPP
  2. Many significant extrusions are removed by natural processes; however, this may not be necessary for recovery
  3. Those who do recover often have minimal persistent neurological deficits
  4. There is a wide range of time to recovery of ambulation, but it may not be significantly longer than that following surgical treatment.

What will be the benefits of this research?

This study aims to add to the available evidence for medical management and begin to provide some prognostic data which will enable veterinary surgeons to recommend or support non-surgical management more confidently, especially when financial or geographic constraints prevent surgical intervention. By uncovering the natural history of the disease, this study will also enable future studies to demonstrate more accurately the effect of any intervention on rate of recovery and time to ambulation, allowing a more evidence-based approach to clinical decision making.

Thinking about applying for BSAVA PetSavers’ funding?

This study would not have been possible without BSAVA PetSavers’ funding. MRI is an expensive imaging modality and an integral part of our research and, without funding, performing repeat MRIs on our cases as per our protocol to document the fate of extruded material would have been cost prohibitive. Clinical research trials are important for informing the diagnosis and management of disorders in clinical practice, and BSAVA PetSavers provides a vital source of funding for anyone hoping to undertake this form of research.

References
1. Freeman P and Jeffery ND (2017). Re-opening the window on fenestration as a treatment for acute thoracolumbar intervertebral disc herniation in dogs. Journal of Small Animal Practice 58(4): 199-204.
2. Langerhuus L and Miles J (2017). Proportion recovery and times to ambulation for non-ambulatory dogs with thoracolumbar disc extrusions treated with hemilaminectomy or conservative treatment: a systematic review and meta-analysis of case‑series studies. The Veterinary Journal 220: 7-16.

Biographies 

Sam Khan

Sam graduated from the Royal Veterinary College in 2017. During a rotating small animal internship at the Queen’s Veterinary School Hospital in 2019/2020, he developed an interest in neurology and canine intervertebral disc extrusions which led to his current position as a PhD student at the University of Cambridge.

Paul Freeman

Paul has had a varied career spanning more than 30 years, beginning his working life as a mixed general practice vet. He developed a role as a referral orthopaedic surgeon, before beginning an alternative track residency in neurology based at Cambridge University in 2008. This led eventually to the European Diploma in Veterinary Neurology in 2014, as well as RCVS and European Specialist status. Paul became Principal Clinical Neurologist at the Queen’s Veterinary School Hospital, University of Cambridge in 2016, and since that time the neurology service in Cambridge has grown rapidly. Paul now works with four senior specialist colleagues, as well as supervising three residents and two PhD students. His main research interests are spinal cord injury, in particular canine intervertebral disc disease. Paul has published many studies and reviews since beginning his career as a neurologist and has lectured widely both in the UK and overseas. In 2020 he co-authored a new textbook of neurology aimed at general practitioners which was very well received and will be translated into Chinese next year.