Disk Disease

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Introduction

Breeders have bred dogs over many years to obtain a certain look or to enhance specific qualities. One of the more significant tradeoffs with this breeding is the propensity for some breeds to have problems with their bone structure. In some dogs this affects the spinal cord. At the least it causes discomfort, but unfortunately, it can cause more severe problems, including complete paralysis. When it occurs it is called intervertebral disk disease (IVD). It is one of the most common diseases causing paralysis of the rear legs in dogs. It is not a common disease in cats.

Neuroanatomy and physiology is a world all by itself, and is far too complex to cover completely in this page. It will be summarized and generalized for much easier understanding.

One of the most significant treatment modalities for IVD is called VOM. We will talk about it more in the treatment section.

It is helpful to be aware of some of the medical terms involved with IVD:

Vertebral Anatomy

The dog has 31 vertebrae:

• Cervical (neck)- 7
• Thoracic (chest) - 13
• Lumbar (lower back) - 7
• Sacral (pelvis) - 3 (fused)

Let's go on a tour of this anatomy by looking at overlapping radiographs:

C-1 and C-2 are called the atlas and the axis. There can be an instability in this area in large dogs that will cause neurologic problems.The cervical vertebrae are quite flexible, for obvious reasons. Disk disease can occur in this area.

As the cervical vertebrae become the thoracic vertebrae they go past the shoulder (S). The nerves that come off this cervical-thoracic junction at the shoulder are called the brachial plexus (you cannot see nerves on a plain radiograph). They innervate the front legs on each side. Each of the thoracic vertebrae corresponds to a rib (R) on each side of the chest.

As we continue down the thoracic vertebrae you can visualize how high their dorsal spinal processes are.Also notice how these processes start to get smaller as we get closer to the lumbar vertebrae. Thoracic vertebrae in this area do not typically cause disk disease.

Moving towards the end of the thoracic vertebrae we come to what is termed the thoracolumbar (T-L) junction. It is a very common area to have disk disease. As we pass into the lumbar vertebrae we have now made our way into the lower back.

The 7 lumbar vertebrae eventually lead into the sacral vertebrae. The fused sacral vertebrae are hard to visualize because they are within the pelvis. After the sacrum we are at the tail.

Spinal anatomy

The spinal cord is an extremely sensitive part of the nervous system. In essence, it is an extension of the brain. as the spinal cord moves from the brain down to the tail it sends out nerve branches (called nerve roots) that go to various organs. Some of these nerve branches bring sensation back to the brain. If you are painfully pinched on your skin it is the nerve branches in your skin that relay a feeling of pain from the skin, to a local nerve branch, and eventually along your spinal cord to your brain. At the same time that these nerve impulses are going to the brain to tell you it hurts, there are other nerves in the spinal cord that go to the muscle near the area of pain and cause a reflex movement away from the pain. The nervous system is so sophisticated and sensitive that it actually stimulates your muscles to contract so you can move away from the painful stimulus without your brain having to tell the muscles to contract. Your brain perceives the pain, but by the time you feel the pain your muscles have already contracted.

These nerve branches that come off the spinal cord are very complex and overlap with other nerve branches. This makes localization of the exact nerve branch that is causing the problem a complex diagnostic problem. Added to the fact that our patients do not talk to us, the diagnostic challenge in figuring out exactly where on the spinal cord a dog is having a problem is no simple undertaking, and usually needs the aid of a specialist.

This side view of a spinal cord model shows 2 vertebrae (V) with a normal disk (D) in between. One of the nerve roots (NR) can be seen coming off of the spinal cord (SC).

To keep you oriented, this is the same area on a radiograph (at L1-2). The nerve root comes out of the dark structure that looks like a horse's head. The disk, nerve root, and spinal cord do not show up normally on a radiograph. If the disk material becomes calcified it might show up.

This view of a spinal cord model is an end-on view of how the spinal cord fits into the spinal canal. You can see how the spinal cord is enclosed by bone. If it swells it has no place to expand into, resulting in serious damage to the cord.

Pathophysiology of IVD

Classification

Type I

It occurs commonly in chondrodystrophic breeds starting as early as 4 months of age. The disk loses its moisture content and starts to mineralize. The stresses of daily living cause it to degenerate, ultimately rupturing its contents into the spinal canal and putting pressure on the nerve roots and spinal cord. The pressure can be so great that the blood supply to the spinal cord can be damaged also, leading to actual death of spinal cord tissue (myelomalacia). Eventually, these dogs will die of respiratory failure.

In IVD disease the disk material (red) in the space between the vertebral bodies puts pressure on the spinal cord and the nerve root that is leaving the spinal cord.

Type II

This version of IVD occurs in larger dogs starting around 5 years of age. The changes in the disk occur much slower than in Type I disk disease. The disk bulges but does not actually rupture into the spinal canal. The spinal cord is not as severely injured and usually maintains its normal function.

The above classifications are helping in understanding IVD, but they do not always apply in every case. Large breed non-chondrodystrophic dogs can get Type I disk disease, and chondrodystrophic breeds can get Type II disk disease.

Degree of Damage

It is important to note that the speed at which a ruptured disk extrudes its material into the spinal cord is equally as important as how compressed the spinal cord becomes. Some dogs with minimal compression of the spinal cord can have severe neurologic problems because disk material extruded rapidly and severely damaged the spinal cord.

Cause

Trauma to a normal disk can cause disk material to extrude into the spinal canal. The most common cause is the natural degeneration of the disk that occurs in the chondrodystrophic breeds when young, and the larger breed dogs as they age. In most chondrodystrophic breeds it is the thoracolumbar area, the junction of the last few thoracic vertebrae and the first few lumbar vertebrae, that are involved.

Symptoms

The symptoms that occur vary from mild to severe. Much of it depends on which vertebrae is involved, how long the problem has been present, and whether the problem is Type I or Type II. It is important to follow the diagnostic processcarefully when making a diagnosis.

The cervical (neck) vertebrae tend to have larger spinal canals for the spinal cord to pass through than do the vertebrae of the mid and lower back. When a disk puts pressure (whether Type I or Type I) the spinal canal has more room, so the spinal cord is subject to less compression in the neck than in the mid and lower back. Less compression means there is less of a chance that paresis or paraplegia will occur.

The following symptoms tend to occur with cervical disk disease:

• Crying

  Especially when the neck is manipulated or when lowered to eat or drink

• Poor appetite (anorexia)

  Pain can sometimes be so severe as to interfere with appetite

• Muscle spasms and reluctance to move

  Another sequelae to the pain that can occur

• One or both front legs might be lame

  Nerves to the front legs come out of the spinal canal at the cervical vertebrae.

• Ataxia

  Pressure on the spinal canal at the cervical vertebrae can interfere with the nerves that innervate all 4 legs. Only rarely will this cause tetraplegia (paralysis).

When IVD occurs at the junction of the thoracic and lumbar (thoracolumbar) vertebrae, symptoms might be different than in the cervical version. Some of these symptoms depend on whether there is a Type I or Type II problem.

• Crying in pain or shaking

  A consistent symptom noticed by owners is their dog crying as if something hurts. It might happen spontaneously, or it might happen when you pet or pick your dog up. Those of us that have had a pinched nerve understand how severe this pain can become.

• Reluctance to move

  This might manifest itself as a hesitation to jump onto the bed, reluctance to go up or down stairs, or just laying around more than usual.

• Poor appetite (anorexia)

  The pain that occurs can decrease the appetite.

• Ataxia to rear quarters

  A dog might walk around as if the back end is going in a different direction than the front end. This is caused by pressure on the nerve roots that go to the rear legs.

• Paraparesis or paralysis to rear legs

  The pressure on the nerve root can become so severe that it can completely impair the nerve and cause paralysis.

• Tense abdomen

  This is called referred pain, and can mimic the symptoms of other diseases.

• Hunched appearance

  An additional problem related to pain

• Fecal or urinary incontinence

  These are relatively severe signs of thoracolumbar disease

This dachshund is exhibiting signs of pain to its rear quarters. His tail is between his legs and his abdomen is hunched up.

This dog is "down" in his rear quarters, a potential sign of IVD disease.

This dog is exhibiting serious signs of IVD. It is partially paralyzed in its rear legs.

When the problem progresses to this point these dogs commonly will not be able to urinate. The urine needs to be manually expressed before it passively overflows. Urine that stagnates in the bladder causes discomfort, stretches the muscles in the bladder wall so much so that muscle tone will not return, and sets up the stage for a bladder and kidney infection. This radiograph outlines the distended bladder of a dog with this problem.

Diagnosis

Since the symptoms of IVD disease mimic those of other diseases, a thorough approach is needed to differentiate them. In every disease we encounter we follow the tenet's of the diagnostic approach to ensure that we make an accurate diagnosis and that we do not overlook some of the diseases that are also encountered in pets as they age.

1.Signalment

IVD disease can occur at any age, although it tends to be a problem that affects middle aged and older dogs.

Several canine breeds are prone to getting IVD. They are called chondrodystrophic due to the shape of their bones from breeding:

• Dachshunds
• Welsh corgi
• Lhasa apso's
• Shih Tzu's
• Cocker spaniels
• Bulldogs
• Beagles
• Pekingese

2. History

IVD disease is suspected in any pet that has some of the symptoms described above, especially if the dog seems in pain or has some degree of paralysis. Falling or being hit by a car gives us a clue that the spinal cord might be damaged.

3. Physical Exam

Routine physical exam findings might include:

• Shaking
• Increased heart and respiratory rates
• Pain upon abdominal palpation
• Pain when moving the neck
• Weakness to the back end
• Lameness to any of the legs

During your dogs exam you will notice one of our doctors checking some reflexes. This exam helps localize the problem and helps to verify that the problem is indeed IVD and not some other problem. Four of the more common neurologic tests will be explained:

Panniculus

This test is performed by poking the skin gently with a needle. If the pin is felt the muscles underneath will cause the skin to temporarily "crawl". By finding the junction where the skin no longer crawls it is possible to help localize the nerve root (remember, they overlap). The affected nerve root is usually 1-2 vertebrae in front of the spot where the skin crawls.

Proprioceptive deficits

This is a postural reflex that tests the ability of a dog to recognize the placement of one of its limbs without actually seeing it. This tests the ability of the nerve to respond to the abnormal sensation to a foot that is bearing weight on the wrong surface.

When the wrong surface is bearing this weight it sends a signal from the nerves in the top of the foot to the spinal cord segment innervated by that foot. When the signal gets to the spinal cord segment it also travels to the brain signaling that the foot is in an abnormal position. The brain then sends a signal back down the spinal cord to the muscles that innervate the foot telling them to contract and put the foot back into normal position.

This is a sensitive test, and if a dog does not return its foot to a normal position immediately it potentially indicates a serious problem with the spinal cord.

It is easily performed by placing the foot in an abnormal position. This dog should have returned its foot to a normal position immediately. Other diseases besides IVD can cause this problem (ex.- a fractured leg)

Knee jerk (myostatic)reflex

This is a spinal reflex that tests the ability of the spinal cord to react to stretching of the patellar tendon. If absent or diminished it indicates a potential problem with the nerve root. If exaggerated it indicates a potential problem with the spinal cord. Other tendons besides the knee can be checked for this reflex.

Every pet has a different response to this stimulus, so it is usually repeated for accuracy.

Deep pain (withdrawal) reflex

In this reflex a toe is pinched, which normally will result in withdrawal of the limb away from this painful stimulus. This occurs independent of whether or not the pain is perceived at the brain level (you already learned this at the beginning of this page in the spinal cord anatomy section). Apet with a problem in its spinal cord will have the reflex, but will not realize it is painful because the nerves that travel along the spinal cord to the brain are injured.

Dogs that show no reaction when a painful stimulus is applied to their legs are considered to have severe spinal cord injury. These dogs carry a poor prognosis for recovery. This is a subjective test though, and needs to be performed numerous times for proper interpretation. Some dogs don't consciously show signs of pain, so this critical test can be misinterpreted.

4. Diagnostic Tests

Radiography

In some cases an x-ray is the diagnostic test of choice. Radiographs help determine if a dog's pain or paralysis is due to IVD or some other cause. Other causes can include trauma, tumors, cysts, or infections of the vertebrae.

Dogs that have IVD might have calcified disks, collapsed disks, even calcified disk material in the spinal canal. Dogs that are radiographed for IVD disease must be under general anesthesia for proper technique and positioning.

This dog has spondylosis, which is a form of arthritis due to instability of the vertebrae. This is not necessarily IVD disease. Some dogs with this arthritis are in pain and need medication, while others have no symptoms at all.

Cats can get spondylosis also, although it is more common in dogs.

This radiograph of a Pug named addison shows a collapsed disk along with spondylosis between L- 2 and L- 3. You can tell it is collapsed when you compare it to the disk in front and behind.

This dog has IVD disease. There is calcified disk material in the spinal canal between L-2 and L-3, and it is painful and weak in its rear legs.

 

This radiograph is from an 11 year old dog that is weak on one of its rear legs. The arrow points to the involved vertebrae. Foreign bodies and infections are possible causes, but most likely it is a tumor.

This is the same dog but from the VD view.

Myelogram

As good as an x-ray is in making this diagnosis, it is far from adequate in many cases. Plain x-rays do not allow visualization of the actual spinal cord or nerve roots. The dye injected during a myelogram outlines the spinal cord and allows much better visualization of any pathology in the cord. Injecting a radiopaque dye into the spinal canal is almost mandatory for a diagnosis, and is of critical importance if surgery is contemplated.

This myelogram is outlining the spinal cord in the lumbar vertebrae of a dog. The vertical column of dye at the top is where the needle was inserted to inject the dye.

Magnetic Resonance Imaging (MRI)

This tool is available to veterinarians and is very valuable in making a diagnosis of spinal cord disease. If the myelogram is inconclusive the MRI can provide valuable information on the health of the spinal cord.

This myelogram is outlining the spinal cord in the lumbar vertebrae of a dog. The vertical column of dye at the top is where the needle was inserted to inject the dye.

Cats can get spinal lesions also. This is the radiograph of a 15 year old cat with a lesion in its spinal canal at the arrow. This cat is painful and not walking well on its rear quarters.

This is the x-ray and MRI report on this same cat.

Treatment

Treatment depends on the severity of the problem and whether the problem is Type I or Type II. Fortunately, in many cases, especially if caught early, conservative therapy can be beneficial. Pets that have recurring problems might eventually need surgery.

Cage Rest

This is the most important treatment modality short of surgery. Cage rest means exactly what is says; there can be no running, jumping, or playing. a crib or playpen will not work because dogs will try to jump out. It sometimes has to be utilized for several weeks for an adequate outcome.

Dogs that are cage rested need to be monitored carefully for progression of the problem. Serial neurologic exams are used to monitor their condition. They should be hospitalized for the first few days in order to monitor their progress.

Medication

Anti-inflammatory and analgesic medications are used routinely in Type I disease. Medications are highly beneficial in reducing pain and minimizing inflammation at the delicate spinal cord. The mainstay when it comes to medication is cortisone. Muscle relaxants are also used to minimize the spasms that accompany this problem. It is imperative that any pet with IVD that is put on medication is under strict cage rest. Pets that feel better with medication might be inclined to resume their normal activity, greatly increasing the chance that their spinal cord will suffer more damage. Our goal is to give just enough pain medication to make the dog more comfortable, yet not so much that the dog resumes its normal activity. If a dog's condition improves with cage rest it should be continued for up to 3 weeks. Exercise should be restricted for an additional 3 weeks. Unfortunately, recurrence is common.

Dogs that are unable to urinate properly due to this disease might also be put on antibiotics to prevent urinary tract infections.

Dogs with Type II are routinely placed on anti-inflammatory medication. There are many highly effective ones available to veterinarians that greatly enhance a dog's quality of life.

Surgery

Surgery is the treatment of choice for recurring problems, dogs that have not improved with conservative therapy, or those that have neurologic deficits. Dogs that are paralyzed (paraplegic) in the back legs need immediate surgery. During the surgery the goal is to relieve the pressure on the spinal cord. This is done by removing a piece of the vertebral body or cleaning out the disk material that is putting pressure on the cord.

Surgery is also used to verify a diagnosis since the actual spinal cord can be visualized. In addition, even if the prognosis for recovery from paralysis is poor, surgery can minimize pain at the spinal cord if an owner is willing to deal with the long term paralysis.

Post operative care is important in dogs undergoing back surgery. They might need hydrotherapy, manual expression of their bladders, controlled walking with assistance, and lots of TLC.

This chart gives an idea of how these treatment modalities are used. These are not hard and fast rules, but more of a guideline.

Medical Therapy	Surgical Therapy
First episode of pain only	Several episodes of pain only
First episode of paresis or mild ataxia	Several episodes of paresis or mild ataxia
Medical conditions that prevent surgery	Condition that worsens with only medical therapy
Paralyzed and no deep pain response for > 48 hours	Mild paralysis with deep pain response present
Symptoms of progressing myelomalacia	Paralyzed and deep pain response present for less than 48 hours

A paralyzed dog can lead a very high quality of life. These dog carts work quite well.

Acupuncture

A relatively new treatment modality for IVD in dogs is acupuncture. It can be helpful in dogs that are not paralyzed or in those where anesthesia or surgery are contraindicated. It is important to remember that it does not always work, and the prolongation of other treatment modalities should not be undertaken due to the severe and potentially irreversible nature of this disease.

Dr. P wanted to make sure the needle did not hurt an already painful dog, so he volunteered to be the "pain guinea pig". He is happy to report that there was no problem (and he could now actually dunk a basketball!).

Here are the needles in use in addison (the Pug whose x-rays you saw previously).

VOM

In the last few years our doctors have been using this treatment method in almost every case of IVD when the pet is not paralyzed. It has changed the way we look at this disease, and give us a new tool to treat without the use of drugs. OurVOM page has more details.

Prognosis

IVD is a serious and potentially crippling disease. If your dog exhibits any of the previously described symptoms it needs an immediate exam by one of our doctors. If the problem is caught early enough the outcome of this disease is usually satisfactory. If you own one of the breeds that is predisposed to this disease it is important to closely observe for the symptoms of IVD disease.