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IVDD/IVDH - Background

Cervical intervertebral disc disease is just one possible diagnosis your veterinarian should consider when your dog appears to have a cervical spinal issue.

While helpful, neck X-rays can be unreliable. If the patient is not sedated or is positioned incorrectly for the X-ray, false findings may appear, or actual issues might be missed. In these instances, proving or disproving a diagnosis is not always possible.

Degeneration of IVDs can be invisible on standard X-rays, whether the disc remains in its proper location or has protruded or extruded. X-rays that appear “normal” don’t necessarily exclude the diagnosis of IVDH. Disc space narrowing (smaller space between adjacent vertebrae) seen on an X-ray of a dog with signs may suggest a disc herniation but can’t prove that disc herniation at that site is the cause.

Dogs with signs of cervical IVDH may first have milder signs that still are unchanged or mild first signs that increasingly worsen, including progression to weakness or paralysis, or they may start out with more severe initial signs of weakness or paralysis.

Signs and their progression depend on several factors, including the force with which the spinal cord is impacted, the amount of spinal cord and/or nerve root compression, and the degree of inflammation present.

If your dog has signs of neck pain alone, your veterinarian may perform a neurologic exam to ensure there are no other issues that may have been missed. This exam will include watching how your dog walks and moves their head and neck and checking for muscle spasms, coordination, and reflexes in the limbs. X-rays may be ordered, but as said previously, X-rays may not be reliable.

If your dog shows severe signs or signs that aren’t improving with medical treatment and rest, your veterinarian may refer you to a surgeon for evaluation. More severe signs are less likely to improve or may not improve quickly with non-surgical treatments alone.

Your Dog’s Spine

All mammals, including your dog, have spines made up of individual bones called vertebrae. The spine is divided into five areas:

• Cervical (neck)
• Thoracic (chest)
• Lumbar (lower back)
• Sacral (between the lower back and the tailbone)
• Caudal or coccygeal (tailbone or tail)

The Spinal Cord

The spinal cord is the communication trunk for the body’s central nervous system, connecting the body with the brain. The spine acts as a bony tube that protects the spinal cord. To allow movement, joints, ligaments, muscles, and tendons connect the individual vertebrae.

Between each vertebra (except the first two neck vertebrae) are cushiony wafers called intervertebral discs, or IVDs. These discs are made of a tough outer ring of fibrous tissue and an inner jelly-like material, serving as shock absorbers for the vertebra. 

Intervertebral Disc Disease

IVDs are subject to several possible diseases, called intervertebral disc disease or IVDD. Health issues affecting the backbone commonly relate to aging and worsen over time. The soft inner material of the IVD loses its water content and becomes stiff and fibrous (fibroid degeneration). This process usually goes unnoticed because the discs have no sensory nerves.

Less cushion between the discs creates more movement between the adjacent vertebral bones, which can produce bony spurs. These spurs may join and partially fuse the vertebrae. The spurs are not painful but can be seen on X-rays. IVDs, whether normal or undergoing degeneration, are, in general, invisible on X-rays.

The other type of degeneration is called chondroid (cartilage-like) metaplasia, which is seen in dog breeds that resemble dwarfs with short, curvy limbs.

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This type of degeneration is genetic and begins early in life. Studies have shown that about 90% of dogs in these breeds will have evidence of this form of IVDD by the time they reach one to two years of age. 

With chondroid degeneration, the discs will undergo mineralization/calcification, meaning calcium builds up in tissues and hardens into mineral deposits. Mineralized discs can be seen on X-rays.

Signs related to IVDD appear when the disc moves out of its standard location and presses against either the spinal cord or the nerve roots that come off the spinal cord. This kind of disc disease is more common with discs that already have some level of degeneration. In people, this is called a “slipped disc”.

The medical term for this is disc herniation, or IVDH (intervertebral disc herniation).

IVDH

The three significant forms of disc herniation are:

• disc protrusion: a lump of disc bulges against nerve roots or the spinal cord
• disc extrusion: a rupture of the outer disc layer causes a mass of the inner jelly-like portion of the disc to impact on and/or compress the nerve roots of the spinal cord
• ANNPE (acute, non-compressive nucleus pulposus extrusion): The disc nucleus ruptures, impacting the spinal cord but leaving no residual compression.

It is uncommon for simple IVD degeneration to result in IVDH (meaning most animals with IVDD, even if it can be seen on X-rays, won’t have any symptoms as a result); however, the chondrodystrophic breeds have a higher risk for IVDH as mentioned above.

Signs of Cervical IVDH

Pain is the most common and often the only sign of disc herniation in the neck. Your dog may be reluctant to:

• walk or play,
• eat or drink from bowls on the floor,
• go up or down steps or stairs,
• move their head and neck from side to side.

Most of these signs are due to nerve root compression from the herniated disc. Sometimes, with disc herniations in the mid and lower part of the neck, this nerve root compression may result in signs in the forelimb served by that nerve root. In people, this is reported as tingling, a pins-and-needles sensation, pain, or weakness in an arm. Dogs may be seen limping or holding a forelimb up.

Root Signature

Dogs might limp, hold up a front leg, or lick a paw. This is called a “root signature”.  These signs may make you think there is a problem with the leg itself, such as joint, bone, or muscle pain. If issues with the front leg’s bones, joints, and muscles are ruled out, and especially if there is neck pain, a “root signature” may be the cause.

Signs of Spinal Cord Injury

Neurological deficits can result when the spinal cord is injured by compression from a herniated disc. Signs include paresis (weakness) and ataxia (incoordination). Your dog may trip or stumble, and their body may veer from side to side. Their limbs may cross over themselves, or they may have trouble getting up and walking. With a cervical disc herniation, the signs will affect all four limbs. The hind limbs may be more affected, or weakness may be more severe on one side than the other.  

In cases of severe weakness, your dog may be unable to walk without help or at all (paralysis). More severe neurologic issues may mean a poorer prognosis or a slower recovery.

Please see: Cervical IVDD (Intervertebral Disc Disease) in Dogs - Diagnosis and Treatment