The first report of Intervertebral disc (IVD) disease in a dog was published in 1881 and involved a Dachshund with acute onset of hind limb paralysis. It would take over 40 years for the condition to be correctly described in veterinary literature. IVD degeneration is an imminent effect of aging in dogs. These changes may cause acute herniations (extrusion) or chronic herniations (protrusion) leading to spinal cord compression causing painful neurological defects.


During the 1950s studies of IVD degeneration in dogs were performed by the Swedish veterinarians Hansen and Olsson. This led to first clear description of intervertebral disc degeneration and herniation and explained the distinction between chondrodystrophic (CD) and non-chondrodystrophic (NCD) breeds with regard to this process. The literal translation of chondrodystrophy is “cartilage maldevelopment”. Examples of chondrodystrophic breeds are Dachshund, French Bulldog, Pekingese, Beagle, Basset Hound, and Shih Tzu. Microscopic analysis of the bones of puppies from these CD breeds demonstrated that their short stature is due to defects in which cartilage is replaced with bone in the developing limb.


There are two (most) common types. Classic Type I disc disease is common in small breed, CD dogs. Part of their intervertebral disc undergoes changes resulting in decreased water content, subsequent mineralization causing altered disc biomechanics. Continued abnormal forces on the disc cause the dorsal portion to weaken, and the mineralized center is acutely extruded into the vertebral canal causing a sudden onset of painful neurologic dysfunction. Signs of Type I disc disease are rarely noted prior to two years of age.


In Type II IVD disease it typically occurs in NCD, large breed dogs. With this type of disc degeneration, there are fibrous changes to the disc and concurrent degeneration. This degenerative process leads to bulging of the central part with gradual dorsal protrusion into the vertebral canal. Clinical signs of Type II disc disease are most commonly observed in geriatric animals, greater than 7 years or age. Pain and neurologic dysfunction in these cases results from chronic compression of the spinal cord and nerve roots. Of the NCD breeds, the German Shepherd dog (GSD) is at the highest risk of developing IVD degeneration and disease (at the lumbosacral junction) due to an altered joint angle causing a disproportionately high workload on the neighboring IVDs, predisposing it to degeneration.


Degeneration of the IVD is an aberrant, multifactorial, response to progressive structural failure of the IVD. Due to specific changes, the matrix of the IVD becomes more rigid and loses its hydrostatic properties to function as a cushion. The inability of the IVD to fulfil its physiological function interferes with the normal action of the vertebral column, thereby influencing other components of the functional spinal unit (ligaments, facet joints, and vertebral bodies). Degeneration can lead to structural failure of the functional spinal unit and ultimately to spinal cord compression. The degenerative changes ultimately cause the IVD to bulge outwards when it is subjected to loading. There is a validated grading scheme for IVD degenerative neration but does not include herniation and prolapse of the IVD, which are consequences of the degeneration, but does not include herniation and prolapse of the IVD, which are consequences of the degenerative process.


Next week we will continue to explore Intervertebral Disc Disease