What is Chiari(-like) malformation (CM)?
In Chiari-like malformation, part of the cerebellum protrudes through the opening at the back of the skull, known as the foramen magnum. This is not normal. Normally, the brain should have enough space within the skull, but in some dogs:
- the space at the back of the skull is too small
- the shape of the foramen magnum is abnormal
- the balance between brain size and skull size is unfavourable
This results in compression of brain tissue.
In dogs, the term Chiari-like malformation is used because it is a combination of:
- a relatively large cerebellum
- an undersized cranial cavity
- sometimes an abnormally shaped foramen magnum
The idea that these dogs have “too much brain” is incorrect. They actually have proportionally less brain tissue than large dogs, but the distribution and available space are unfavourable.
Which dogs are affected by CM?
CM mainly occurs in small and very small breeds, including:
- Cavalier King Charles Spaniel
- Chihuahua
- Pomeranian
- French Bulldog
- Griffon breeds
- Papillon
In the Cavalier King Charles Spaniel, CM is found in almost all dogs, often without obvious symptoms. In other breeds, such as the Pomeranian, CM is seen in around 60% of dogs.
Symptoms of Chiari malformation
Not every dog with CM shows symptoms. When present, they may include:
- head shaking
- air licking
- frequent swallowing
- pain when the head or neck is touched
- squinting
- restlessness or irritability
Symptoms may appear at a young age, but CM itself is congenital and usually does not change significantly with age.
What is syringomyelia (SM)?
Syringomyelia is a condition in which fluid-filled cavities develop within the spinal cord. This happens due to a disruption in the flow and pressure of cerebrospinal fluid.
These cavities can:
- remain small and cause few symptoms
- grow larger and damage nerve tissue
The larger and more unfavourably positioned the cavity is, the more severe the symptoms usually are.
SM can only be diagnosed using an MRI scan.
Which dogs are affected by syringomyelia?
SM often occurs in the same breeds as CM, particularly:
- Cavalier King Charles Spaniel
- Pomeranian
- Chihuahua
- French Bulldog
It is estimated that around 60% of Cavaliers develop SM, compared with about 25% of Pomeranians. Not every dog with SM shows clinical signs.
Symptoms of syringomyelia
The main symptom of SM is pain. This pain is often:
- intermittent
- difficult to detect during examination
- worse during excitement, exercise or weather changes
Common signs include:
- sudden yelping or crying out when moving
- phantom scratching, scratching without touching the skin
- sensitivity when the neck, chest or shoulders are touched
- unusual sleeping positions, such as with the head raised or supported
- a curved neck or back, especially in young dogs
- weakness or muscle wasting in severe cases
At what age do symptoms start?
In some dogs, symptoms only appear later in life, sometimes after several years, which makes early detection difficult.
- CM is congenital and present from an early age
- SM can develop gradually over time
How is the diagnosis made?
The only reliable way to diagnose CM and SM is with an MRI scan. MRI clearly shows both the brain and spinal cord. CT scans are not sufficient for this purpose.
There are:
- screening MRI scans for breeding purposes
- comprehensive MRI scans for dogs showing symptoms
Treatment of CM and SM
There are several treatment options to help manage the symptoms of CM and SM.
Medication, most commonly used
Treatment is usually focused on pain relief and improving comfort:
- pain relief medication
- drugs for neuropathic pain, such as gabapentin or amitriptyline
- medications that reduce the production of cerebrospinal fluid
- as a last resort, corticosteroids
Surgery
Surgical treatment is possible, but:
- it is technically very complex
- it often provides only temporary improvement
- there is a high risk of symptoms returning
For this reason, medical management is usually preferred.
Prognosis
The prognosis varies greatly between dogs:
- dogs with mild abnormalities may remain symptom free
- dogs with severe SM may experience lifelong pain
- with proper management, an acceptable quality of life is often possible
Breeding and prevention
CM and SM mainly occur in breeds that have historically been selected for specific physical traits. These conditions are an important concern within breeding programmes and make preventive measures essential, such as:
- responsible breeding practices
- MRI screening of breeding dogs
- avoiding selection for extreme physical features
- prioritising health over size or appearance
In breeds where screening is mandatory, such as the Cavalier, improvements are already being seen. Voluntary screening in other breeds can help prevent a great deal of animal suffering.
Chiari malformation and syringomyelia are serious conditions that mainly affect small dogs. Not every dog with CM or SM will show symptoms, but when they do, these can be extremely painful. Early recognition, accurate diagnosis, appropriate treatment and responsible breeding are essential to protect the welfare of these dogs.
If you suspect your dog may be showing symptoms, always contact a veterinarian with experience in neurology.
Source: veterinair-neuroloog.nl
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