Symptoms & Treatment Methods for Pet Intervertebral Dis

What is IVDD and Why Does It Occur?

Many people are familiar with the basic skeletal anatomy of the spine, which remains relatively consistent across species. Dogs, for instance, have 7 cervical vertebrae, 13 thoracic vertebrae, 7 lumbar vertebrae, 3 fused sacral vertebrae, and a few coccygeal vertebrae, depending on the breed and conformation. Thick, flexible, and shockabsorbent intervertebral discs separate adjacent vertebrae. These discs are composed of two parts: a tough, thick outer layer called the annulus fibrosus, and a soft, jellylike central part known as the nucleus pulposus. The ends of these structures are covered by tough cartilage caps that attach to each intervertebral disc and vertebra. The vertebral bodies are further connected to the intervertebral discs by ligaments on both the dorsal (upper) and ventral (lower) sides. These longitudinal ligaments contain nerve supplies, and when they are damaged or inflamed, they can cause pain.

In an ideal world, all anatomical structures would remain flexible and elastic throughout an animal's life. However, this is not always the case. Two significant changes can occur in the intervertebral discs, affecting their function and leading to disease:

1. The nucleus (nucleus pulposus) dehydrates and mineralizes, causing it to herniate.

2. Over time, the annulus fibrosus weakens gradually, allowing it to bulge into the spinal canal and compress the spinal cord.

Hansen Type I and II Intervertebral Disc Disease

Shortlegged dogs (chondrodysplasia) often begin to experience degenerative changes and mineralization in their intervertebral discs as early as 2 to 24 months of age. This degenerative process and mineralization typically occur rapidly in puppies. The dehydration and mineralization of the nucleus pulposus make it easier for the nucleus to herniate through tears in the annulus fibrosus into the spinal canal, leading to acute and severe spinal cord injuries. This type of disc herniation is known as Hansen disc disease. Dogs with chondrodysplasia, particularly Dachshunds, are genetically predisposed to this condition. In this type of herniation, there is a high risk of severe spinal cord damage.

Hansen Type II intervertebral disc disease usually occurs in larger breeds, such as German Shepherds and Labrador Retrievers. Type II disc disease is characterized by the gradual onset of clinical symptoms in affected animals. The affected discs gradually bulge into the spinal canal, compressing the spinal cord and spinal nerve roots, leading to weakness. If the condition worsens suddenly, these animals may experience severe pain.

Clinical Symptoms of the Disease

Clinical symptoms vary depending on the type of intervertebral disc disease. Dogs with Type I intervertebral disc disease are often young (34 years old) and belong to shortlegged breeds, such as Dachshunds and Basset Hounds. These dogs typically exhibit severe neck or back pain of varying degrees. Neurological dysfunction varies depending on the severity of the spinal cord injury.

Dogs with Type I disease may walk with their necks bent, unwilling to lift their heads, or not allowing their necks to bend side to side. Touching these animals' heads or necks may cause them to shrink, bark, or try to bite. If a dog walks with a hunched back, struggles to lie down, moves slowly, or growls when their abdomen is touched, these can indicate back pain. They may refuse to jump on or off furniture, use stairs, or react negatively to being touched. Pain can range from mild to severe, even chronic.

Dogs with Type II intervertebral disc disease are usually older (812 years old) and belong to large breeds, such as German Shepherds. They may exhibit mild or no back pain and a gradual progression of weakness in their limbs. Occasionally, these dogs may experience acute pain and present with the same symptoms as dogs with Type I disease.

The Five Grades of IVDD

The severity of neurological signs can be categorized into five grades:

1. Back or neck pain without loss of function in the limbs.

2. Paralysis of the limbs, but the animal can still walk.

3. Paralysis of the limbs and inability to walk.

4. Paralysis with deep pain sensation intact.

5. Paralysis with no deep pain sensation.

The severity of the disc herniation and the extent of spinal cord injury determine the presentation of Type I intervertebral disc disease in dogs, which can include any of the abovementioned conditions. Dogs with Type II intervertebral disc disease typically present with a stage of weakness in movement but can also progress to paralysis.

To determine the extent of your pet's neurological disease, your veterinarian will perform a comprehensive neurological examination. Your pet will be evaluated for pain, weakness, normal reflexes, the ability to place and move limbs correctly (motor function), and the ability to be aware of the position of their limbs (proprioception). The pet's light touch skin and the sensation of pinching between the toes will be assessed. Deep pain is the body's response to pressure on the toes—specifically, the reflexive withdrawal of the limb. The inability to feel pain and not responding to pain indicates severe spinal cord damage. If you suspect your dog has neck or back pain or any of the neurological symptoms discussed above, you must seek veterinary treatment immediately.