Syringomyelia in dogs: phantom scratching, pain and care

Overview

A fluid-filled cavity is also called a syrinx. Several cavities may occur at different points in the spinal cord. A cavity can disrupt normal spinal cord function. This can cause abnormal sensations or nerve pain.

Chiari-like malformation is abbreviated to CM and syringomyelia to SM. They are different findings, although they often occur together. A cavity on MRI may also be found in a symptom-free dog. The finding is therefore assessed alongside symptoms and examination results.

Cavities may be round or divided into compartments.

A cavity may be localised or extend along almost the whole spinal cord.

Causes

Cerebrospinal fluid circulation is disrupted

In Chiari-like malformation, brain tissue size and the space inside the skull are mismatched. Crowding at the back of the skull may push the cerebellum into or through the foramen magnum, the opening at the skull's base. This disrupts normal cerebrospinal fluid flow around the brain and spinal cord. Abnormal flow and pressure may create cavities inside the spinal cord.

At this crowded junction, the brainstem may also move towards the foramen magnum.

Dilation of the spinal cord's central canal is called hydromyelia. When distinguishing a cavity from central canal dilation is difficult, the term syringohydromyelia may be used. A presyrinx is spinal cord swelling around the central canal before an obvious cavity forms.

Not every cavity is caused by Chiari-like malformation

Syringomyelia may also occur with injury, a tumour or inflammation. Other structural diseases that disrupt cerebrospinal fluid circulation can also underlie it. The skull malformation is present from birth even if symptoms appear later.

Risk factors

The disease mainly affects small and short-skulled breeds. A short, broad, domed skull and a crowded back part of the cranial cavity predispose dogs to syringomyelia. In Pomeranians, a body weight below 2.5 kg has been associated with more frequent syringomyelia.

Syringomyelia has been found in about half of Cavalier King Charles Spaniels examined. Cavities have been reported in about 40% of Chihuahuas. The corresponding proportion in Pomeranians has been 24%. These figures describe imaging findings, rather than symptomatic disease in all dogs.

Chiari-like structural changes have been found in about 94–100% of Cavaliers. This differs from a spinal cord cavity finding. In a large study of Cavaliers screened for breeding, sex did not significantly affect the likelihood of a cavity.

Syringomyelia has been reported in about 20% of Affenpinschers examined. In Pomeranians, the reported proportion with Chiari-like malformation has been 55%.

The prevalence of syringomyelia increases with age. In a British study, 25% of Cavaliers examined at one year old had syringomyelia. In those examined over 6 years old, the proportion was 70%. Symptoms most often begin in the first few years of life and usually by 6 years of age.

Typical symptoms

With phantom scratching, a dog makes scratching movements beside the head, neck or shoulder without touching the skin. It may turn its head towards the scratching leg at the same time. An abnormal sensation may trigger the movement even when there is no itchy skin condition.

• Your dog scratches the air beside its skin.

• Your dog repeatedly rubs its face.

• Paw licking increases.

• The neck, areas around the ears, shoulders or back are sensitive to touch.

• Your dog yelps when running, jumping, being picked up or defaecating.

• Your dog resists having a collar or harness put on.

• Your dog withdraws and is reluctant to play or go for walks.

• Front leg steps become stiff.

• The front legs weaken or become lame.

• The neck twists to one side.

• Neck muscles may waste.

• Nervousness, aggression or repeated air licking increases.

Pain may be more obvious at night or when your dog gets up after resting. Touch, movement, excitement or a collar can trigger symptoms. Symptoms may fluctuate.

Owners report that being in season or changes in the weather may sometimes worsen symptoms.

Complications and consequences

Pain and spinal cord damage affect daily life

A cavity can cause progressive poor coordination and limb weakness. Nerve pain has been described in about 40–70% of cases. Complete recovery may not be possible because of the underlying structural abnormality and spinal cord damage.

Most symptomatic dogs deteriorate over time. In about a quarter, symptoms remain unchanged or improve. Nevertheless, many dogs can retain good quality of life with long-term treatment and monitoring.

Some dogs remain stable for years, while others lose function within months. Anticipating pain may make a dog less willing to be handled.

Diagnosis at the vet

Pain, scratching and other diseases are investigated

The examination establishes symptom onset, the situations in which they occur and changes in neurological function. Skin and ear diseases can cause similar head rubbing or scratching. Other causes of neck pain include a slipped disc, infection of vertebrae or discs, and tumours. Instability of the first neck vertebrae can also compress the spinal cord.

MRI shows the cavity and skull junction

MRI is the first-choice investigation. It shows skull shape, brain position and fluid-filled cavities in the spinal cord. Imaging is usually performed under general anaesthesia to keep the dog still. An ordinary X-ray does not provide the same information about cavities.

Investigation of a symptomatic dog may include imaging the whole spinal cord as well as the brain. Cavities may lie beyond the neck and do not always form a continuous lesion. A cavity wider than 4 mm that is asymmetrical and extends into the spinal cord's dorsal horn is more likely to be associated with symptoms.

About half of symptomatic Chihuahuas and Pomeranians have no visible spinal cord cavity. The corresponding proportion in Cavaliers is about 10–20%.

What do grades in an official SM screening scheme mean?

In one official screening classification, SM0 means a normal finding with a central canal diameter below 1.0 mm. SM1 means a central canal of 1.0–1.9 mm. SM2 means a canal or separate cavity at least 2 mm wide, or a presyrinx. An S is added to the grade for a symptomatic dog.

Chiari-like malformation is assessed separately with a CM grade. CM2 means the cerebellum is pressed into or herniates through the foramen magnum. The CM grade alone does not describe the full degree of crowding at the back of the skull.

In CM0, the back edge of the cerebellum is normally rounded. In CM1, this edge is indented but a fluid space remains visible between the cerebellum and foramen magnum. The letter a in the assessment means the dog is over 5 years old. The letter b means 3–5 years old. The letter c means an imaging age from 18 months to 3 years.

MRI for an official assessment under this scheme usually takes about 30–60 minutes. The report also records the size of the brain's lateral ventricles. It additionally assesses whether the middle ears contain material. A separate symptom description is submitted for official assessment of a symptomatic dog.

Treatment

Treatment aims to manage pain and function

The vet tailors care to your dog's symptoms and quality of life. Gabapentin or pregabalin may be used for nerve pain. Pregabalin reduces the release of substances transmitting pain signals in the spinal cord. A non-steroidal anti-inflammatory drug such as meloxicam or carprofen may form part of treatment.

A corticosteroid is also used in some situations to reduce inflammation. Medicines such as omeprazole may be used in an attempt to reduce cerebrospinal fluid production. Medication does not usually remove the underlying structural change completely. Many dogs need pain management for the rest of their lives.

Surgery may relieve pressure, but symptoms can return

In severe cases, decompression surgery at the back of the skull can reduce crowding. The procedure removes bone from the back of the skull. Recurrence rates of 25–47% have been reported after surgery. In about half, symptoms return within 2–2½ years of the operation.

Existing spinal cord damage may remain permanently even after surgery. Physiotherapy may support muscle weakness and coordination difficulties. The effectiveness of pain treatment is usually assessed every 1–3 months.

Everyday changes reduce pain triggers

A harness may suit your dog better than a collar when pressure on the neck provokes symptoms. Different harness designs may need trying to find an individual fit. Raising food and water bowls may keep the neck in a more neutral position. Avoid touching particularly sensitive areas during grooming.

Concurrent skin allergies and ear diseases are treated so they do not add to discomfort. Reducing stress and anxiety may also make daily life easier. Exercise does not need the same restriction in every dog.

Prevention

Syringomyelia has a polygenic basis, involving the combined effects of several genes. No single gene variant explaining the disease has yet been identified. Some breeding guidance excludes symptomatic dogs from breeding. It also uses MRI to check symptom-free breeding dogs for cavities.

Under some official screening schemes, a symptom-free dog must be at least 18 months old at imaging for an official assessment. A symptomatic dog can receive an assessment at a younger age. A young dog's normal imaging result may change later. Under such schemes, repeat imaging is usually performed no sooner than 6 months later, although new symptoms may prompt an earlier examination.

Breeding decisions take age at imaging into account. Breed organisations provide more detailed mating recommendations based on results.

The relationship between parental MRI results and findings in offspring was examined in a group of 340 dogs. The odds of an offspring having a cavity rather than none were 3.08 times as high when both parents were affected as when both were clear. The 95% confidence interval, expressing statistical uncertainty, was 1.58–6.04. In that study, changes as small as 0.5 mm were counted as cavities.

Its disease definition was therefore broader than the SM2 screening classification described above.

Important for dog owners

Take short videos of phantom scratching and painful episodes if you can do so without touching your dog. Record the time, symptom duration and circumstances: resting, walking on a lead, excitement or being picked up. Note sleeping, play, eating and willingness to go outside too.

Symptoms may change, so medication effectiveness needs regular monitoring. Alongside pain-related behaviour, monitor limb strength and coordination.

Ask for a written plan explaining when to contact your vet about changing symptoms. Agree how to assess a medicine's benefits and possible adverse effects. Do not provoke scratching by pressing a painful neck simply to record a video or test the symptom.

Frequently asked questions

Is phantom scratching the same as itchy skin?

During phantom scratching, the leg makes scratching movements without touching the skin. An abnormal nerve sensation may underlie it. However, skin and ear diseases can cause similar head rubbing or scratching. Diagnosis therefore also requires investigation of other causes of scratching.

Can an MRI finding be symptom-free?

Yes: both Chiari-like malformation and syringomyelia may be found in a dog without clinical symptoms. The location and significance of the finding are compared with the symptoms. A symptom-free result in a young dog does not rule out syringomyelia developing later.

Can Chiari-like malformation cause pain without a cavity?

Yes: crowding or Chiari-like malformation at the skull–neck junction alone can cause symptoms. In small dogs, symptoms are therefore not always associated with a visible spinal cord cavity. MRI and ruling out other causes of pain help guide treatment.

Does surgery cure syringomyelia permanently?

Surgery can reduce pressure at the back of the skull, but symptoms may recur. Reported recurrence rates after surgery have been 25–47%. Many dogs still need long-term pain management and monitoring even if surgery helped the initial symptoms.

Does my dog need constant rest?

Exercise does not automatically need restricting in every dog with syringomyelia. A suitable harness may reduce neck pressure that triggers symptoms. Pain-provoking situations and the ability to manage everyday movement determine which changes help your dog. Physiotherapy may support muscle weakness.