Syringomyelia (SM) is a neurological condition where fluid-filled cavities (syrinxes) form within the spinal cord. In dogs, it is almost always associated with Chiari-like malformation (CLM) — a structural abnormality where the skull is too small for the brain, forcing the cerebellum to push toward the spinal cord and disrupting normal cerebrospinal fluid (CSF) flow. The result is pressure and turbulence that damages the spinal cord over time. SM causes chronic, often severe pain and is one of the most distressing conditions seen in certain toy breeds.
Which Breeds Are Affected?
Syringomyelia linked to Chiari-like malformation is strongly associated with brachycephalic (short-skulled) toy breeds, particularly:
- Cavalier King Charles Spaniel (CKCS): The most severely affected breed. Studies suggest over 70% of CKCS have Chiari-like malformation, and a significant proportion develop SM. It is considered the breed-defining health crisis for Cavaliers.
- Griffon Bruxellois (Brussels Griffon): Extremely high prevalence due to similar skull conformation.
- Chihuahua: Elevated risk, though often milder presentation.
- Yorkshire Terrier, Maltese, Miniature Dachshund, Miniature/Toy Poodle: All have documented cases.
SM can also occur secondary to other spinal conditions (tumors, trauma, inflammation) in any breed, but the Chiari-linked form is the most clinically significant and common presentation in dogs.
Causes and Pathophysiology
In Chiari-like malformation, the brain is too large for the skull — or more precisely, the occipital bone at the base of the skull is underdeveloped. This forces the caudal cerebellum (hindbrain) through or toward the foramen magnum (the opening where the brainstem meets the spinal cord), compressing brain tissue and obstructing CSF flow.
Normal CSF circulates in a pulsing wave coordinated with the heartbeat. When this flow is obstructed at the craniocervical junction, CSF pressure becomes abnormal and the spinal cord is subjected to repeated hydraulic stress. Over time, this causes fluid to be drawn into the spinal cord itself, forming the syrinx cavities. As the syrinx expands, it compresses and destroys the nerve pathways running through the spinal cord, causing progressive neurological deficits.
The severity of SM does not always correlate predictably with the degree of Chiari malformation on MRI. Some dogs with significant herniation have no syrinx; others with minimal herniation develop large syrinxes. This is one reason SM management is complex.
Signs and Symptoms
The hallmark sign of SM in dogs is phantom scratching — the dog scratches at the shoulder, neck, or behind the ear without making contact with the skin, or only lightly touching. This occurs because abnormal sensory signals from the damaged spinal cord create a sensation of itching or pain that the dog cannot localize accurately. It is often triggered by exercise, excitement, or being on a leash (collar pressure).
Other common signs include:
- Neck and shoulder pain: Dogs may cry out when picked up, resist head movement, or hold the head in an abnormal position.
- Sensitivity to touch: Dogs may react dramatically to gentle touching of the ears, head, neck, or back — out of proportion to the stimulus.
- Scoliosis: Curvature of the spine, often toward the side of the syrinx.
- Weakness or incoordination (ataxia): In more advanced cases, the syrinx disrupts motor pathways, causing stumbling or difficulty walking.
- Facial pain or rubbing: Some dogs rub their face repeatedly, suggesting cranial nerve involvement.
- Sleep disturbance: Pain often worsens at rest or at night, causing restlessness and insomnia in affected dogs.
Symptoms typically begin between 6 months and 3 years of age, though some dogs develop signs later in life. The severity varies enormously — some dogs have mild, manageable symptoms; others progress to severe neurological deficits.
Diagnosis
Syringomyelia is definitively diagnosed by MRI (magnetic resonance imaging). MRI is the only imaging modality that can visualize the syrinx cavities within the spinal cord and the structural abnormalities of the craniocervical junction. X-rays and CT scans are not adequate for diagnosing SM.
MRI is performed under general anesthesia. The entire brain and cervical spine are imaged, allowing assessment of the degree of Chiari malformation, the location and size of any syrinxes, and the extent of CSF obstruction. This information guides treatment decisions.
Spinal fluid analysis (CSF tap) may be performed concurrently to rule out inflammatory or infectious causes of similar symptoms. Neurological examination by a veterinary neurologist before and after MRI provides a clinical picture of which functional pathways are compromised.
Treatment and Management
Treatment depends on the severity of symptoms, the size and location of the syrinx, and the dog’s overall health. Both medical and surgical options are available.
Medical management aims to reduce CSF pressure and control pain. It does not reverse the structural malformation or the syrinx, but can effectively manage symptoms in many dogs for extended periods:
- Omeprazole: Reduces CSF production, decreasing pressure within the syrinx. It is often used as a first-line treatment and is well-tolerated.
- Furosemide (diuretic): Also reduces CSF production, sometimes used in combination with omeprazole.
- Gabapentin or pregabalin: Neuropathic pain medications that address the abnormal sensory signals causing phantom scratching and hypersensitivity. Often highly effective for pain control.
- NSAIDs: Reduce inflammation and provide additional pain relief, used alongside neuropathic agents.
- Corticosteroids: May be used short-term during flares of severe pain, but long-term use carries significant side effects.
Surgical treatment (foramen magnum decompression) aims to address the root structural cause. The surgeon removes bone at the back of the skull to enlarge the foramen magnum, relieving compression and restoring more normal CSF flow. Many dogs show improvement in pain symptoms after surgery. However, surgery does not eliminate the syrinx and does not guarantee permanent relief — recurrence of symptoms occurs in approximately 40–50% of dogs within 2–5 years as scar tissue reforms. Surgery is typically considered for dogs who do not respond adequately to medical management or who are deteriorating neurologically.
Harness use instead of a collar is recommended for all dogs with SM to avoid collar pressure on the neck, which can worsen symptoms.