Cauda equina syndrome in dogs: back pain and treatment

Overview

Cauda equina is Latin for horse's tail, which the bundle of nerve roots resembles. These nerves control functions including hindleg and tail movement and bladder and bowel control. Narrowing may be within the spinal canal or a nerve root's exit opening.

Degenerative lumbosacral stenosis is abbreviated to DLSS. It is one possible cause of cauda equina symptoms, rather than a shared diagnosis for all lower back diseases. Many dogs with degenerative narrowing have lower back pain alone. Clear neurological deficits are less common in the degenerative form.

The fibres in this nerve bundle tolerate compression better than spinal cord tissue itself, partly explaining why pain predominates.

Causes

The disc and surrounding tissues narrow the space for nerves

Degeneration mainly affects the L7–S1 disc between the last lumbar vertebra and the sacrum. The disc loses water as degeneration progresses. As the disc space becomes narrower, the nerve exit openings also shrink.

The outer ring of the disc may bulge against the nerve roots. Thickened ligaments may add to compression. Joint degeneration and bone growth around the joints can narrow a nerve root's passage. Compression does not affect the same part of the nerve bundle in every dog.

Loading and posture affect the narrowing

Extension at the lumbosacral junction normally narrows nerve root openings too. Degeneration may exaggerate this movement-related narrowing. Pain may arise from both tissue damage and nerve irritation. Tumours, inflammation, injury or congenital abnormalities can also compress nerves in the same area.

Risk factors

A typical patient is a large, middle-aged or older dog. The disease is particularly characteristic of German Shepherd Dogs. Repeated heavy spinal loading in working and sporting dogs may contribute to degeneration. Lumbosacral disease has also been described in small dogs.

Symptoms of degenerative narrowing usually start at 3–7 years of age. In large case series, mean ages at diagnosis or treatment have been 5.5 and 5.8 years. In series not composed mainly of working dogs, the male-to-female ratio was over 1.7:1.

A lumbosacral transitional vertebra, or LTV, predisposes the junction to early degeneration. LTV is a congenital, inherited structural abnormality. Its precise inheritance mechanism is not yet known. A dog with an LTV may have no clinical symptoms.

Dogs with degenerative lumbosacral stenosis often weigh more than 25 kg.

Typical symptoms

Pain often appears as reduced activity and reluctance to jump. It may be more obvious on stairs, uphill or when jumping into a car.

• Your dog gets up slowly or cautiously from a soft resting place.

• Jumping or using stairs causes a growl or yelp.

• One hindleg becomes lame after exercise or is briefly held bent.

• Hindleg muscles become smaller and strength decreases.

• Hind claws or paws wear from dragging.

• The tail wags less effectively or hangs limply.

• Urine or faeces pass without voluntary control.

Pain or reluctance associated with jumping, rising or stairs has been described in about 90% of patients. Pain during back examination may cause avoidance or defensive behaviour.

Lower back pain can resemble hip pain. Lameness may worsen during prolonged exertion. Your dog may hold its lower back more arched than usual.

Complications and consequences

Nerve damage may remain after pain improves

Severe nerve root compression can cause hindleg paralysis. Permanent nerve damage is not reversed simply by removing compression. Urinary incontinence present before surgery may not improve afterwards. Loss of bowel control can also be permanent.

Compulsive biting of the tail or paws can damage the skin. Symptoms may return after initially successful treatment. Coping at home does not automatically mean a dog can return to heavy work.

Possible surgical complications

Removing a vertebral joint process can increase instability at the junction unless it is also supported. The joint process on the opposite side may also fracture under excessive structural loading.

Diagnosis at the vet

The back, hips and nervous system are assessed together

Diagnosis combines symptoms, clinical examination and imaging findings. The vet locates pain by examining the lumbosacral junction and limb function. The hips are assessed separately because hip disease and spinal narrowing may occur in the same dog. Pain on hip extension alone does not reliably establish its source.

The neurological examination assesses findings including hindlimb reflexes and muscle wasting. The reflex around the anus and tail tone help assess lower nerve function. Clear balance or limb position awareness problems also require investigation for other neurological diseases. The cause of urinary incontinence is investigated separately too, as it may be another concurrent problem.

The knee reflex may remain normal despite lower nerve root dysfunction. It can also appear exaggerated because the muscles that bend the knee have poor tone. This apparently brisk reflex must not be confused with a sign of damage higher in the spinal cord.

Images are interpreted in light of symptoms

X-rays look for conditions including fractures, infections, bone tumours and vertebral abnormalities. However, degenerative changes may also appear in a symptom-free dog. Ordinary X-rays do not show nerve roots or disc tissue in sufficient detail.

MRI shows nerves and other soft tissues. CT shows the area's bony structures in three dimensions. Imaging in different positions helps identify movement-related nerve root narrowing. The degree of compression seen does not always match symptom severity.

MRI can identify disc dehydration as a loss of its normal bright signal. Electromyography may show impaired muscle nerve supply in more severe cases. However, the diagnostic reliability of electrical nerve testing still needs further investigation.

Treatment

Conservative care for mildly affected dogs

The vet plans treatment according to symptom severity and the cause of narrowing. Degenerative narrowing mainly causing pain is often treated initially with medication and reduced strain. When mild pain is the only symptom, 4–6 weeks of rest may help. Jumping, climbing, strong twisting and sharp turns are avoided.

Controlled lead exercise follows the initial strict rest. Reducing excess weight helps manage spinal loading. Pain relief may include meloxicam, for example. Gabapentin may be used for nerve-related pain.

Some dogs may receive a corticosteroid into the epidural space around the nerves. Methylprednisolone injections have been reported to benefit about 80% of dogs with pain and only minor neurological deficits. The injection procedure may require anaesthesia. Medication can relieve pain even though structural narrowing remains.

In a separate injection-treatment series of 38 dogs, 30, or 79%, improved. In the same follow-up, owners reported 20 dogs to be symptom-free at a median follow-up of 48 months. Dogs with neurological deficits had been excluded from that series.

Rehabilitation and monitoring treatment outcomes

Physiotherapy may strengthen trunk muscles supporting the lower back. Strong comparative evidence of rehabilitation effectiveness is still lacking. Water-based rehabilitation is not recommended for every dog with this narrowing.

In one conservatively treated group, 17 of 31 dogs, or 55%, had a successful outcome. In the same group, 10 dogs, or 32%, went on to surgery after medical treatment failed. Three dogs, or 10%, were euthanased because symptoms progressed. In another group of 16 dogs, 50% of owners rated the outcome as good. In that group, 25% of dogs had recurrent symptoms during follow-up.

Surgery is chosen according to the compression site

Surgery is considered for persistent pain, inadequate response to medication or neurological deficits. Dorsal laminectomy creates space for nerves by removing bone from the vertebral arch above them. Foraminotomy widens a narrowed nerve root exit opening. Sometimes vertebral movement is reduced by fixation with screws or another support structure.

About 70–95% of dogs improve after surgery. Fixation screws can loosen, bend or break. Scarring at the surgical site may leave nerve root pain. A few days of hospital care for pain relief are usually needed after surgery.

After widening the exit opening, outcomes were rated good or excellent in 19 dogs in a series of 20. Mean follow-up in that surgical group was 15.2 months.

Rest and an individual rehabilitation plan are also needed after surgery. Long-term changes in exercise habits may be necessary. If bacterial discospondylitis causes the symptoms, antimicrobial treatment targeting the bacteria is also required.

Prevention

Some official X-ray screening schemes assess congenital lumbosacral transitional vertebrae. Under such schemes, an official LTV assessment may be available from 12 months of age. This screening concerns a congenital vertebral change. A screening image alone does not establish the cause of lower back pain developing later.

In such schemes, an official LTV assessment may be issued only once for a dog because the change being screened for is congenital. LTV0 means that these vertebral changes were not found.

Some breeding guidance recommends excluding dogs with symptomatic LTV from breeding. Under that guidance, symptom-free dogs with LTV1–LTV4 results are paired only with LTV0 dogs. Spinal X-rays of their offspring are recommended to gather information.

Important for dog owners

Record when pain began, the amount of exercise and movements after which your dog becomes lame. Note getting up, jumping, stairs, tail use and bladder and bowel control separately. Do not try forcefully raising the tail or pressing the back at home to locate pain.

Soft, thick bedding is part of supportive care. Walking can be assisted by supporting your dog under the abdomen just in front of the hindlegs.

Ask for practical instruction on lifting and support before home care starts. Agree how exercise will progress and when follow-up will take place. Monitor function as well as pain: can your dog toilet, does the tail move and does each hindleg bear weight as before?

Frequently asked questions

Is cauda equina the same as lumbosacral stenosis?

Cauda equina is the name of the nerve root bundle, and the syndrome describes symptoms arising from its damage. Degenerative lumbosacral stenosis is one common cause. Inflammation or a tumour can also damage nerve roots in the same area and cause symptoms.

Does an LTV finding mean painful back disease?

No: an LTV is a congenital vertebra with features of both a lumbar and a sacral vertebra. It may predispose a dog to early degeneration. A dog with an LTV may also be symptom-free. A clinical diagnosis of narrowing requires agreement between symptoms and more detailed investigations.

Can my dog be treated without surgery?

Many mildly affected dogs can initially be treated with rest, pain relief and changes in activity. When mild pain is the only symptom, 4–6 weeks of rest may help. Persistent pain or neurological deficits may instead require surgery.

Will surgery restore bladder control?

It may not return to normal even if back pain eases and movement improves. Permanent nerve damage is not reversed by removing compression. Urinary incontinence may also result from another concurrent disease, so its cause is investigated separately.

Can my dog return to its previous activities?

Returning to demanding work is less certain than coping in a quiet home environment. Permanent changes to the amount or type of exercise may be needed even if initial treatment eases symptoms. Jumping, strong twisting movements and climbing may be among the activities to avoid.