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Intervertebral disc disease

Carl Gorman BVSc MRCVS

Key words: Laser, intervertebral disc, chondrodystrophic, wobbler, rupture

 

Intervertebral disc disease (IVDD) is a common disorder in dogs, but a rare one in cats.  It refers to an abnormality of the disc or discs between vertebrae in the spine, which usually results in protrusion of material from the disc into the spinal canal.  This results in pressure on the spinal cord.  Depending on the severity of the protrusion, signs can range from pain to neurological deficits and even to permanent damage of the cord with resultant paralysis.

Intervertebral discs consist of a tough fibrous outer ring, theannulus fibrosus, and a gelatinous inner core contained by the annulus, thenucleus pulposus.  Together they serve to act as connectors between the vertebrae and shock absorbers for the spine. (Fig 1)

LA8F1

Fig 1:  Anatomy of an intervertebral disc.

Causes of disc disease

Although it is possible for trauma to the spine to cause damage to a disc, the vast majority of cases in dogs are a result of degenerative disease.  As a disc ages, the proportion of water in the disc reduces, making it less flexible and more prone to damage.  Other factors are stress and anatomy.  Hence a long backed dog, classically the dachshund, puts an increased load on the thoracolumbar spine compared to a shorter backed dog.  Very active dogs will also place extra demands on their intervertebral discs.

Abnormalities of the vertebrae can be another source of stress on discs.  Wobbler syndrome is normally found in large dogs such as Great Danes, or in Dobermans.  One or more vertebrae in the neck are misshapen and this can either put direct pressure on the spinal cord (often when the neck is flexed or extended) or the instability caused by the abnormal vertebra will wear the disc abnormally, leading to early rupture.

As the disc degenerates the annulus fibrosus becomes thinner or weaker allowing protrusion of material or rupture.

Discospondylitisis an infection of one or more intervertebral discs.  This is not uncommon in dogs, though again it is rare in cats.  Infection is normally spread via the blood from a remote source such as a urinary tract, skin or prostatic infection.  The infection process may cause local swelling, e.g. from a granuloma, or extra bone to be formed.  This places pressure on the spinal cord.  Severe infections may cause pathological fractures, and it is possible for infection to spread to the epidural space, resulting in meningitis or an epidural abscess.

Types of disc disease

Degenerative disc disease takes one of two types, known as Hansen Type 1 or 2 protrusions.

Hansen Type 1  disc disease occurs when the outer annulus fibrosus becomes weakened over time and the nucleus pulposus becomes calcified.  Eventually the annulus ruptures, allowing the sudden escape of calcified material into the spinal cord.  The acute compression caused brings on signs rapidly. (Fig 2)

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Fig 2:  Hansen's type 1 disc protrusion - the annulus fibrosus has ruptured allowing nucleus material to escape into the spinal canal.

This type of disc disease is commoner in chondrodystrophic breeds, which have longer backs and shorter legs relative to other breeds.  Dachshunds, corgis, basset hounds, Pekingese and cocker spaniels are examples. (Fig 3) Dogs are often quite young when affected, between 3 and 6 years of age.  Several discs may be involved.

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Fig 3:  Dachshunds are an example of an chondrodystrophic breed, prone to Hansen's Type 1 disc protrusions.

Hansen Type 2  disc disease is a slower process, where weakening of the annulus fibrosus gradually allows nucleus pulposus to bulge into the spinal canal.  Non-chondrodystrophic breeds such as retrievers, German shepherds and Dobermans are susceptible.  The onset of the disease is slower, often affecting dogs between 8 and 10 years old, and the signs come on more gradually.  Fewer discs tend to be affected than with Type 1 disease.  (Fig 4)

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Fig 4:  Hansen's type 2 disc protrusion - the annulus fibrosus has weakened allowing the nuclear material to bulge into the spinal canal.

Localisation of lesions

The region of the spine where the disc protrusion is located can be deduced if neurological signs are present.  Recognising upper motor neuron (UMN) and lower motor neuron (LMN) signs is important when recognising the site of damage.  Table 1 gives a simplified differentiation between the two.

Clinical test

Upper motor neuron

Lower motor neuron

 

 

 

Reflexes

Exaggerated

Reduced

Muscle tone

Increased or spastic

Decreased

Fasciculation

Absent

Present

Muscle atrophy

None

Severe

                                         Table 1:  UMN vs LMN signs

                              (Fasciculation is involuntary muscle twitching)

Fig 5 shows the divisions of the spinal cord for neurological purposes. 

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Fig 5:  Sections of the spine.  Intervertebral disc lesions can be localised to these sections depending on the signs seen.  Remember that more than one disc is often involved.

Table 2 shows the signs which lesions in each spinal segment might produce.

 

Spinal segment

Thoracic limb signs

Pelvic limb signs

Notes

 

 

 

 

Cervical (C1 - C5)

UMN

UMN

May show absent or decreased postural reactions in all 4 limbs

Cervicothoracic (C6- T2)

LMN

UMN

May show decreased or absent postural reactions in all 4 limbs

Thoracolumbar (T3- L3)

None

UMN

Spinal reflex

Pelvic limbs may show decreased or absent postural reactions

Upper Lumbosacral  (L4 - L6)

None

LMN

Decreased or absent patellar reflex

Intact  withdrawal reflex

Lower lumbosacral (L7-S3)

None

LMN

Decreased or absent withdrawal reflex

 

Decreased to absent perineal reflex

LMN Bladder signs

                                                        Table 2:  Localisation of spinal lesions

Note that the presence and severity of signs depends on the degree of spinal cord compression.  Signs might be limited to pain and discomfort.

 

Diagnosis

Intervertebral disc disease is initially suspected by the history (including breed), clinical signs and examination.

Plain radiographs may show:

  • Reduction in joint spaces
  • Calcified material in the spinal canal or Intervertebral disc spaces
  • Reduction or alteration of the intervertebral foramen (shaped like a horse's head)

Plain radiographs are unable to detect or assess the cartilage and soft tissue in discs, and so more advanced imaging may be required to make a diagnosis and identify the site of the lesion. Myelography (injecting radiopaque material into the subarachnoid space) was the gold standard, but has been supplanted by CT and MRI scanning.  Myelography is accessible to most practices, however, and may still provide a cost effective method of confirming the diagnosis.  Figure 6 shows a myelograph of cervical vertebrae, where protrusion of the discs has caused deviations of the column of contrast in the spinal canal.

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Fig 6: A myelogram in a dog.  Disc protrusion at C5-6 and C6-7 has caused deviation of the column of contrast material.

Treatment

Surgery

Severe cases, such as those showing quadriplegia or paraplegia, are likely to require surgical intervention to decompress the spine.  If deep pain reflexes are absent then the case becomes an emergency.  When assessing deep pain sensation, it is important not to be fooled by spinal withdrawal reflexes, which occur without the patient being aware of the stimulus.  The patient must show a conscious reaction to the stimulus for the deep pain sensation to be present.

Milder cases, particularly those only showing signs of pain or mild postural deficits, may be managed conservatively with strict rest.  Where there is a disc protrusion, strict rest means at least 2 weeks cage rest.  80% of these mild cases will improve with conservative management, and there is a 30-40% recurrence rate.   Surgery may be advised to prevent recurrence.

Hemilaminectomy is the commonest form of surgery to decompress the spine in the thoracolumbar area, and fenestration (removing the nucleus material) of the discs in the region may also be carried out to help prevent further episodes.

Cervical vertebral disc prolapses are normally treated by ventral slot decompression.

Medication

When there is pain, non-steroidal anti-inflammatory drugs should be used with or without opiates for additional analgesia.

Low doses of diazepam can be helpful to relieve muscle spasm, which adds to the pain.  The tranquilizing effect can also help if the patient is anxious because of discomfort.

Physiotherapy

Physiotherapy is important in the rehabilitation phase of IVDD after the acute injury phase has passed.  In the early stages of IVDD, massage of the affected areas will help to relieve muscle spasm and improve comfort.  Movement and massage of limbs affected by paresis or paralysis enhances blood flow and stimulates muscles. 

Once the patient is comfortable (either following surgery or conservative treatment) and the risk of further spinal cord trauma is past then more active physiotherapy or hydrotherapy is useful to encourage a return to use of affected limbs, and strengthen muscles in the limbs and the back.

Laser therapy

Low level laser therapy has several potential benefits in IVDD.

Following surgery, laser therapy reduces oedema and inflammation, treats pain and enhances healing.  Daily sessions should be used initially.  Because the tissues being treated are quite deep seated, high energy levels should be used.  At least 10 joules/cm2 is recommended, though higher levels may be beneficial.

A study published in the JSAP (W E Draper, T A Schubert, R M Clemmons, S A Miles; August 2012)demonstrated a more rapid return to walking following hemilaminectomy in dogs treats with laser compared to those which were not (median 3.5 days compared to 14 days).  In this series a power level of 25 joules per cm2 was used.

In less severe cases, or those managed conservatively, laser therapy can reduce pain and inflammation and relieve muscle contracture and spasm.  Treatment should be directed to the spine and muscles at the site of injury and to either side.  Careful palpation will show where muscles are contracted and identify painful foci.  Daily treatment should be used until there is relief of pain, then gradually reduce the frequency of treatments to twice weekly then weekly.

Some studies in rats and rabbits have shown regrowth of neurons and improvement in neurological function when low level laser therapy has been applied,  so there may be potential for repair to spinal cord and nerves, but until further studies have been carried out care should be taken not to make unrealistic claims.