Dr. Larry Carpenter, DVM MS

Diplomate, American College of Veterinary Surgeons

Veterinary Surgical Services

 

FAQs about Disk Disease in Dogs

 

1. What and where is the disk? 

The disk is made up of fibrous connective tissue and serves as a kind of spacer between vertebrae in the backbone.  The disk lies underneath the spinal cord.  The disk is like a jelly donut – with a soft inner part and a tougher outer part:

a) The nucleus pulposus of the disk is in the center and acts as a deformable tissue that is much like a shock absorber for the spinal column.

b) The annulus fibrosis of the disk is a tough fibrous outer layer that holds the jelly-like nucleus in place.

 

2. My doctor says my dog has disk disease, why is this happening to my dog?         

Your dog very likely has a genetic trait that leads to early degeneration of the disk. This is especially true of small breed dogs that are classified as chondrodystrophic.

 

3. What is disk degeneration?

In most dogs and people, the jelly-like inner core of the disk gradually dehydrates with age and becomes less deformable so that it no longer acts as a cushion.  This usually happens late in life for most large breed dogs, but in some small breeds (Dachshunds for example) disk degeneration occurs rapidly; usually before the dog is 2 years old.            

 

4. What happens when a disk herniates?

The mineralized core of the disk is unable to deform with the movements of the dog and is forced upwards through the tough fibrous outer layer of the disk and into the spinal canal.  This material takes up space in the spinal canal and squeezes the spinal cord against the boney interior walls of the canal.  This pressure on the spinal cord results in pain and weakness or paralysis.  The neurological condition caused by disk herniation is variable depending to a large extent on how much of the nuclear core is pushed against the spinal cord and also on how forcefully the material strikes the cord. Onset can be rapid – within minutes of a jump or a fall that initiates herniation – or it may be slower- over a period of hours to days.  The condition is called Intervertebral Disk Disease of IVDD for short.

 

5. What breeds of dogs are most likely to be affected by disk disease?

Dogs that are most susceptible to IVDD are classified as chondrodystrophic breeds.  Chondrodystrophy is a kind of dwarfism.  Dachshunds are by far the most susceptible breed; in fact, they have a 10-12 times higher risk for disk herniation than all other small breeds combined.  Beagles, Poodles, Shi Tzu’s, Pekingese, Bassets and Welsh Corgis are among the other breeds of dogs that routinely get disk disease.  The truth is that individual dogs of almost any breed can have this type of problem if the right circumstances are present.

 

6. Can my dog die from disk disease?

In a low percentage of cases the damage caused by the disk herniation can lead to uncontrollable deterioration of the spinal cord in both directions from the site of the herniated disk.  This deterioration leads to paralysis of all four limbs and ultimately affects vital functions such as breathing which leads to death.  This condition is known as Progressive Myelomalacia.

 

7. How is disk disease diagnosed?

Your doctor will do a neurological examination which usually demonstrates pain and loss of function caused by disk herniation.  The exam will also help to localize the problem to a general area or region of the spinal cord.  We grade the loss of function resulting from disk herniation in the lower back in order to etermine what the prognosis of recovery is and what therapy is most appropriate.  We use the following scale:

                  Grade 1 – Pain

                  Grade 2 – Weak but able to walk

                  Grade 3 – Weak, unable to walk

                  Grade 4 – Paralysis (usually accompanied by loss of bladder function)

                  Grade 5 – Complete loss of feeling

 

8. How is disk disease treated?

Mild cases in dogs that have pain only and minimal loss of function (Grade 1 or early Grade 2) are usually treated with strict cage rest and pain relieving drugs. More serious problems such as extreme weakness or paralysis of the rear legs usually require surgery.  Complete loss of feeling is considered an emergency and surgery should be done as soon as possible (but certainly within 24 hours) to allow any chance of recovering the ability to walk.

 

9. How is the specific location of the herniated disk found?

Special x-ray techniques are needed to highlight the area of the spinal column where the disk has herniated.  Survey x-rays are usually done of the area of the back where the neurologic exam indicates a problem.  When we are planning to do surgery, we need to know the exact location of the herniated disk.  A procedure called a myelogram is the most common way to locate the herniated disk.  A myelogram is a done with the dog under a general anesthetic.  A spinal tap is done and a dye is injected into the space where fluid circulates around the spinal cord.  Once the dye is in place, several x-rays are taken. When a herniated disk is present, the location can be determined because the disk material takes up all of the space around the spinal cord and pushes the dye away.  The spinal cord segments where the disk has herniated are characterized by a lack of dye, seen on the x-ray as a gap or gaps in the white dye columns surrounding the vertebral segment(s) where the disk has come to lie.  The disk and hemorrhage and swelling are keeping the dye from surrounding that particular part of the spinal cord.

      

CT scans can also be used.  A CT scan shows that most of the spinal cord is surrounded by a thin layer of fat that is less dense than the spinal cord itself.  The mineralized disk material can be seen on the CT scan because it is more dense than the epidural fat.  The CT scan shows “slices” of the spinal cord and can pinpoint the location of the disk herniation.  A CT scan can be arranged by scheduling with a scanner in Rapid City.  Scheduling usually requires some lead time and it is not possible to complete a CT scan as an emergency procedure.

      

MRI is considered the “gold standard” for imaging degenerative and herniated disks in the spinal canals of humans and animals.  We do not have access to an MRI machine for animals in the Black Hills area.  MRI for animals is becoming more common and most veterinary schools and large metropolitan veterinary practices have MRIs.  There are several MRIs for animals in the Denver area. MRI and CT are noninvasive and hold little likelihood of causing harm.  So when they are available they may be preferable to a myelogram.  

 

10. What is done during surgery to correct the problem caused by disk herniation?

Once the specific location of the herniated disk has been determined, the surgeon uses specialized equipment to remove the bone that forms the roof over the spinal cord to help relieve the compression.  The disk material then must be removed from around or under the spinal cord with small sturdy instruments.  The nearby disks are usually also fenestrated – that is – the surgeon cuts the outer layer away from the nearby disks and removes the inner core so that it cannot be pushed up into the spinal canal at some future date.

 

11. What is the prognosis for recovery from disk disease?

The prognosis for recovery is related to the degree of damage that the herniated disk has caused to the spinal cord.  For example, dogs that are Grade 1 or 2 have a good prognosis for recovery when either medical or surgical therapy is used. Dogs that are Grade 3 or 4 usually do much better with surgical treatment.  Some dogs that have been paralyzed will have some weakness that remains even after recovery is complete.  Dogs that have a very rapid onset of paralysis may have a somewhat poorer prognosis than those with a slower onset of symptoms.  Even with prompt surgery, dogs that have lost all feeling (Grade 5) have a 50% or less chance of recovering the ability to walk and control urination.

 

12. How important is confinement to the success of conservative therapy for thoracolumbar IVDD?

Strict confinement is crucial and is considered the cornerstone of conservative therapy for IVDD (the dog is kept in the cage at all times and only taken outside to relieve him/herself).  In order to accomplish the goals of preventing further extrusion of the nucleus of the disk and to promote healing of the outer layers (the annulus) of the disk, strict confinement is necessary. Activity can easily push more of the nucleus into the spinal canal and dramatically worsen the neurological status.  It is not uncommon to see dogs that have “gone down” after a short course of pain relievers given without insuring that the owner would enforce strict cage rest.  A typical IVDD case requires up to 6 weeks of confinement.  This time frame is based on the time it takes the annulus to heal by scar formation.  Fibrous  scar tissue takes 3 weeks to begin to be laid down and scar formation reaches its peak at 6 weeks.  So strict cage rest is followed for the initial 3 weeks.  After a recheck exam that shows improvement, slightly more freedom is granted.  At 4 weeks more freedom is allowed if the recheck exam shows substantial improvement.  After 6 weeks have passed, healing should be well underway and the recheck exam should show a more nearly normal neurologic status.  Then cage rest can be discontinued, but lifestyle changes designed to help prevent a   recurrence should be followed – that is weight control, limited stairs and jumping.

 

13. Can this happen to my dog again?

Recurrence of symptoms after recovery is related to the type of therapy used and the activity level and weight of the dog (lifestyle changes).  With medical therapy the chance of having a recurrence of back pain, weakness and/or paralysis can be as high as 34%.  This can be the result of more disk material entering the canal   from the original herniated disk site or it may be a new problem at another disk space.  Limiting activity after recovery is thought to prevent a recurrence of the problem.  This is because susceptible breeds of dogs have multiple degenerative disks in their lower back that are at risk for herniation.

      

With surgery (hemilaminectomy and removal of herniated disk material from the spinal canal) there is still a chance of disk herniation at another site in the lower back.  This chance can be minimized (reportedly to as low as 4-10% recurrence rate) at the time of surgery when the surgeon fenestrates the offending disk space and the 2 adjacent disk spaces.  Because all susceptible thoracolumbar disk spaces cannot be addressed surgically, lifestyle changes and weight control are recommended in surgery patients also.

 

14. How does IVDD in large breed dogs differ from that in small chondrodystrophic breeds?

Large breed dogs rarely have disk extrusions (pushing of the nucleus through the annulus and into the spinal canal) that are common in small chondrodystrophic breeds.  Disk extrusions in small breeds are classified as Hansen Type 1 Disk Disease.  Large breed dogs more frequently have a build up of scar tissue over the outer layer of the disk (the annulus) that pushes up on the spinal cord and gradually causes pain and weakness.  This condition is classified as Hansen Type 2 Disk Disease.  Hansen Type 2 Disk Disease causes slowly progressive neurologic impairment. These dogs are usually older and may not be as painful as the small breeds with Type 1 disease.  Surgical therapy for Type 2 disease may not be as successful for large breed dogs and recovery commonly takes longer than for small dogs.  Hansen Type 2 Disk Disease must be differentiated from other causes of neurologic dysfunction that also affects principally large breed dogs such as Degenerative Myelopathy, Diskospondylitis or Fibrocartilaginous Emboli.  Myelography can be used to help distinguish Hansen Type 2 Disk Disease from these other similarly appearing neurologic conditions of large breed dogs but MRI or CT are generally preferred because these exams are noninvasive and are less likely to make the dog’s condition worse.

 

15. How does cervical (neck region) IVDD differ from thoracolumbar (lower back region) IVDD?

Cervical disk disease accounts for approximately 15% of the Type 1 IVDD cases.  Thoracolumbar disk herniation is responsible for the other 85% of cases in small dogs.  There is more space in the cervical spinal canal around the spinal cord than there is in the thoracolumbar canal.  This characteristic means that cervical disk herniation only very rarely causes compression of the spinal cord that is severe enough to result in neurologic deficits.  Pain is the hallmark of cervical IVDD.  Conservative medical therapy for IVDD is similar to that used for thoracolumbar IVDD, but may not be as successful. Unremitting pain is the primary indication for surgery in cervical IVDD.  Cervical IVDD like thoracolumbar IVDD is also divided into Hansen Types 1 & 2 corresponding to small chondrodystrophic breeds with disk extrusions (Type 1) and large breed dogs who have scarred annulus fibrosis (Type 2 disease and Wobblers Disease).  Surgical therapy for small chondrodystrophic breeds affected with cervical IVDD consists of ventral decompression and disk removal through a ventral slot.  In small chondrodystrophic breeds, fenestration of the remaining cervical discs is thought to help prevent future episodes of cervical IVDD.

 

Intervertebral Disc Disease Medical vs. Surgical Therapy

 

Grade	Symptoms	Success Medical	Success Surgery
1	Pain	~ 100%	97%
2	Ataxia	90-95%	95%
3	Paralysis	80-90%	95%
4	Unable to Urinate	50-80%	90-95%
5	Loss of Deep Pain	15%	~50% within 12 hours

 

Recurrence Rate                         33-50%             4-10%

 

Medical therapy = Administer pain relievers +/- muscle relaxants, 3-6 weeks of Strict Cage Confinement

Surgical therapy = General anesthesia followed by myelogram and decompressive surgery with fenestration of high-risk disc spaces. Expect unassisted walking within 10-14 days.