ABSTRACT Inter-vertebral disc disease (IVDD) occurs when an extrusion or protrusion of inter-vertebral disc material occurs within the spinal cord. Clinical signs of IVDD depend on several factors which include the type of herniation, the location of the lesion, and the extent of the protrusion of disc material into the spinal canal

Prognosis depends on several factors, including the severity of clinical signs before surgery, the rapidity with which the signs developed, and the length of the interval between the onset of problems and surgery. The recovery period may be prolonged and so dedicated nursing care, including physiotherapy, is essential.

Anatomy

The vertebral column consists of a chain of small, unpaired, irregular bones – the vertebrae. These vertebrae encase and protect the spinal cord and extend from the back of the skull to the tip of the tail. Spinal nerves exit through foramina between arches of vertebrae or via arches in the lateral vertebrae.

The spinal cord must remain intact in order to register sensations such as touch and pain, and for normal mobility of the body and limbs. Each vertebra is separated from its neighbour by inter- vertebral discs of fibro-cartilage.1

Inter-vertebral discs are soft tissue structures that allow for normal, limited movement between the vertebrae, and also act as ‘shock absorbers’. The outer fibrous layer, called the annulus fibrosus, acts to contain the inner jelly-like portion, the nucleus pulposus, and prevents it from bulging outwards.

IVDD definition and clinical signs

Inter-vertebral disc disease occurs when an extrusion or protrusion of inter- vertebral disc material occurs within the spinal cord. ‘Protrusion or extrusion of an inter-vertebral disc is a common cause of pain and weakness in dogs’.2

Clinical signs of IVDD depend on several factors which include the type of herniation, the location of the lesion, and the extent of the protrusion of disc material into the spinal canal.

Type I disc degeneration

Type I IVDD results from chondroid degeneration, which affects chondrodystrohic breeds, such as dachshunds, bulldogs and the Cocker spaniel. It is a condition precipitated by a reduction of the water and glycosaminoglycan content of the disc which then causes the disc to calcify.

Type I generally progresses acutely (over hours or even minutes) and tends to be more serious owing to the sudden, large volume of extruded nucleus pulposus through a complete tear of the annulus fibrosis. Depending on the location and extent of the pressure on the spinal cord, there may be pain in the neck region, lack of pain sensation in the limbs, and weakness or paralysis in any – or all – of the limbs.

This is a very serious disease, which may result in permanent hind limb paralysis and incontinence if untreated. Strict cage rest can help initially in some cases, but surgery is often necessary to reduce the pressure on the spinal cord. The outcome will depend on a number of factors, including the severity of clinical signs, whether pain perception is still present, and the length of time between the onset of clinical signs and surgery.

Other spinal conditions that present similarly to type I discs are high velocity-low volume variations of type I discs (type III discs) and fibro-cartilaginous embolic myelopathy (FCE). Both conditions are managed conservatively.

Type II disc degeneration

Type IIIVDD is caused by replacement of disc material with fibrous tissue (fibroid degeneration). This tends to occur in older, larger breeds.

Clinical signs usually develop chronically over a period of months because of the slow and progressive protrusion (bulging) of the annulus fibrosis, through a partial tear. There may be pain, weakness or paralysis in any or all limbs but signs are generally less severe than in Type I, with a slow onset.

Cervical disc disease (CDD)

This tends to occur most frequently in the cervical region of older chondro- dystrophic breeds, which may include dachshunds, the Pekingese and the Cocker spaniel. The C2-C3 disc space is most commonly affected. CDD in large breeds is commonly a type II protrusion of the caudal disc spaces, and can be secondary to spondylomyelopathy (‘Wobbler’ syndrome). Breeds commonly affected are the Doberman and the Great Dane.

The most prominent sign of CDD is neck pain as shown by low head position, stiffness, reduced range of movement, vocalising, muscle spasms of the head ; nd neck, forelimb lameness (nerve root or renal nerve compression), ataxia, neuiulogical deficits, weakness and quadriplegia. The spinal reflexes may be normal, exaggerated, and weak or absent in the forelimbs with a caudal disc extrusion.

The cervical neural canal is much bigger than the spinal cord. This means that disc protrusions in this area will often cause a nerve root impingement, causing pain and the possibility of paresis of one limb rather than severe spinal cord compression. In the thoraco lumbar region, there is barely enough room for the spinal cord in the neural canal and severe neurological deficits that arise from disc protrusions are usually more commonly seen here.

CDD diagnosis and treatment

CDD can be diagnosed by means of the clinical symptoms, a neurological examination, myelography, computed tomography, magnetic resonance imaging and cerebrospinal fluid analysis.

Treatment can include conservative management in the initial stages for patients with no, or only mild, neurological deficits. This includes strict cage rest to promote healing, short-term anti-inflammatory drugs, such as corticosteroids, to reduce spinal cord oedema; as well as, pain management and muscle relaxants to reduce muscle spasm.

If there is no improvement within a week or so (usually a maximum of three weeks), surgery should be considered because this is the only way to remove disc material that causes compression on the spinal cord.

Surgery is the first option in cases that show severe neurological signs, or where there have been repeated episodes of pain and muscle weakness.

Paralysis and loss of deep pain sensation require surgical intervention to remove the pressure on the spinal cord, ideally within a 24- hour period; otherwise permanent nerve damage is likely to occur.

Surgery to remove the extruded disc material and decompress the spinal cord may be achieved through a ventral slot. A window is cut at the ventral surface of the annulus fibrosus of the disc which allows the nucleus pulposus to be removed and reduce protrusion of the material. This is termed fenestration.

Ventral slot surgery is most commonly performed to remove the extruded disc material; however, a dorsal hemi- laminectomy (this is described below for thoracolumbar disc disease) may be required for lateral or far lateral extrusions. In chondrodystrophic dogs, prophylactic fenestration of other inter- vertebral disc spaces during the ventral slot procedure may be required to reduce future risks of IVDD to other areas.

Thoracolumbar disc disease (TLDD)

TLDD commonly affects the T12 -T13 to L1-L2 spaces of young adult to middle- aged chondrodystrophic dogs, such as dachshunds, beagles, and Pugs. Type I extrusions are most common in these breeds, whilst Type II is most common in larger breeds. The signs of TLDD can occur suddenly or gradually, depending on the impact, number of vertebrae affected, location of disc material and duration of disc extrusion.

They include back pain, a reluctance to run, jump or go up steps, kyphosis (curvature of the spine) and neurological deficits, which may vary from a mild ataxia of
the hind limbs to hind limb paralysis along with urinary and faecal incontinence with a lack of deep pain sensation. Spinal reflexes may be normal, exaggerated, and weak or absent when extrusion occurs caudal to L2-L3. ‘Schiff- Sherrington phenomena may cause increased tone in the forelimbs’.1

TLDD diagnosis and treatment

Diagnosis of TLDD can be confirmed through symptoms, a neurological examination, myelography, computed tomography (CT), magnetic resonance imaging (MRI) and cerebrospinal fluid (CSF) analysis. Figures 1 & 2 show MRI scans of a disc lesion at L5-L6.

Figures 1&2: Lateral and sagittal MRI scans of a disc lesion at L5-L6

In less severe cases, conservative treatment (already described for CDD) including bladder management, may be a possibility. However, surgery is required in patients with severe neurological deficits, lack of motor ability and back pain. Patients that have a sudden onset of severe neurological deficits need urgent surgery.

Surgery normally involves a hemi- laminectomy. This is a procedure where the surgeon approaches from the back of the spine to reach the lamina (the dorsal arch) of the vertebrae. After determining the affected disc space, a high speed drill with a bur, is used to remove the lamina on either the right or left side of the vertebral bodies. The removal of the bone allows the surgeon to visualize the spinal cord and the disc which facilitates removal of the disc material. Once the spinal cord is decompressed it can begin the process of healing.

Prognosis

Postoperative prognosis in these patients depends on several factors, including the severity of clinical signs before surgery, the rapidity with which the signs developed, and the length of the interval between the onset of problems and surgery. The recovery period may be prolonged and so dedicated nursing care is essential.

Nursing care includes pain, weight and bladder management. When appropriate, intensive physiotherapy including, massage, passive range of movement, muscle stimulation and therapeutic exercises are also extremely beneficial in the recovery of animals suffering from IVDD, particularly those with motor losses. 

The author wishes lo thank and acknowledge Fitzpatrick Referrals tor the accompanying photographs and input

Author

Sian Norris

BSc IHonsI RVN Dip Animal Physiotherapy

Sian graduated from the University of Reading in 2001 with a Degree in Animal Science. During her spare time at university she worked in veterinary practice, and, after graduating, went on to gain her qualification as a Registered Veterinary Nurse in 2004. Sian has recently completed a Diploma in Animal Physiotherapy and currently works as a ward rehabilitation co-ordinator at an orthopaedic referral centre in Surrey.

To cite this article use either

DOI: 10.1111/j.2045-0648.2011.00086.x or Veterinary Nursing Journal Vol 26 pp 302-304

References

1 GOODY. P. C 119971 Dog Anatomy: A Pictorial Approach to Canine Structure J A Allen London

2 MILLIS. D L.. Levine. D. & Taylor. R A 120041 Canine Rehabilitation & Physical Therapy Saunders. St Louis. Mo.

3 TILLEY. LP & Smith, F W K. 120041 The Five Minute Veterinary Consult. Canine and Feline Lippincott Williams & Witkms. Baltimore

 

• VOL 26 • September 2011 • Veterinary Nursing Journal