Intervertebral disc disease (IVDD) in dogs

by Dr. Mikel Delgado, PhD and Dr. Nate Ritter, DVM

An introduction to the spine

The spine serves multiple important functions for every vertebrate animal - including our pet dogs. The spine supports movement, body weight and structure, and also provides protection for the nerves of the body that run through the spinal cord. These nerves are the channel for signals between the brain and the rest of the body, and when the spinal cord is injured, pain or paralysis can result.

The spine is composed of several small bones known as vertebrae - and the spinal cord passes through them. The vertebrae are connected by the outer fibrous layer of intervertebral discs. The inner, jelly-like part of these discs provides cushion and shock absorption.

How does canine Intervertebral Disc Disease occur?

Problems can arise when these discs degenerate and begin to stiffen, leading to Intervertebral Disc Disease (IVDD). Injuries can occur due to degeneration or a traumatic incident, such as a fall or jump. The discs bulge or burst, pressing into the spinal cord, and leading to a disruption of nerve signals. The result can be pain, nerve damage, or even paralysis.

There are two forms of IVDD. In Type I IVDD, degeneration of the intervertebral discs can begin before a dog is a year old. The gelatinous center (known as the nucleus pulposus) of the discs bursts through the outer layer (annulus fibrosis), pressing on the spinal cord. This is a more severe form of IVDD and it can lead to acute pain, neurological problems, and paralysis. Type I IVDD is seen in several short-legged breeds of dogs, including Dachshunds, French bulldogs, Beagles, and Shih Tzus.

Type II IVDD is more commonly seen in middle-aged, large-breed dogs, and onset may be more gradual. The intervertebral disc bulges, but does not rupture. Type II IVDD can lead to pain and weakness, and increased pressure on the spinal cord.

Are there genetic risks for IVDD in dogs?

IVDD is considered an inherited condition; Type I IVDD is associated with a trait called chondrodystrophy - which is related to the short-legged stature of many breeds. A mutation on the FGF4 gene (chromosome 12) is associated with both chondrodystrophy and an increased risk of IVDD. A separate mutation of the FGF4 gene on chromosome 18 is associated with shortened legs (chondrodysplasia), but not IVDD. Testing dogs for both mutations can allow breeders to select for shorter legs (CFA18-FGF4) if that is the breed standard, without increasing the risk of IVDD (CFA12-FGF4). 

The mutation on chromosome 12 is inherited in an autosomal, semi-dominant fashion, but with incomplete penetrance. Most dogs with two copies of the mutation will have shorter legs than dogs who inherit just one copy of the mutation, and dogs with at least one copy of the mutation are at increased risk of developing IVDD. But, some dogs will be carriers but not affected. 

IVDD is complicated, and there are likely other genetic factors in addition to the effects of the environment (such as exercise and body weight). A dog’s body type can predispose them to stress on the spine, and can end up with an injury regardless of genetics or environmental factors. 

Treatment for canine IVDD

Treatment for IVDD depends on the severity. For some dogs, cage rest and treatment for pain can be helpful in managing symptoms. For other dogs, surgery may be recommended, but the prognosis may be guarded. Because it can be incredibly painful and debilitating, many dogs with IVDD must be humanely euthanized.

Can we prevent IVDD in our dogs?

Breeding decisions related to the CFA12-FGF4 mutation are complicated because of the nature of the expression of the mutation, and because some breed standards would exclude dogs with longer legs. The elimination of all dogs with a CFA12-FGF4 mutation would limit some breeding pools, causing an even greater genetic bottleneck and increasing the risk of other health conditions. Ideally, clear-clear or clear-carrier breedings are prioritized, only breeding two carrier dogs when no alternatives are available. 

Dog owners may be able to further reduce risks for their dogs by keeping them in good physical shape with moderate daily exercise, and by providing ramps and stairs to prevent unnecessary jumping. 

References

VCA: Degenerative Disc Disease in Dogs

American College of Veterinary Surgeons: Intervertebral Disc Disease

Dickinson, P. J., & Bannasch, D. L. (2020). Current Understanding of the Genetics of Intervertebral Disc Degeneration. Frontiers in Veterinary Science, 7.

Fenn, J., Olby, N. J., Moore, S. A., Gjessing, K. M., Davidson, R. M., Levine, J. M., ... & Canine Spinal Cord Injury Consortium. (2020). Classification of intervertebral disc disease. Frontiers in Veterinary Science, 7, 707.

Jeffery, N. D., Levine, J. M., Olby, N. J., & Stein, V. M. (2013). Intervertebral disk degeneration in dogs: consequences, diagnosis, treatment, and future directions. Journal of Veterinary Internal Medicine, 27(6), 1318-1333.