Chiari Malformations in Dogs

Chiari malformations (CM) are a collection of highly heritable neurologic disorders that are believed to result from a variety of malformations of the occipital bone of the canine skull. CM is caused by a discrepancy between the size of the brain and the space within the skull. The space in the skull (caudal fossa) is too small relative to the size of the brain. The result is overcrowding of the brain with herniation of the cerebellum through the foramen magnum (the site through which the brainstem passes). This can cause an obstruction in the normal flow of cerebrospinal fluid (CSF) that surrounds the brain and spinal cord. The resulting pressure leads to a variety of clinical symptoms (see below).

Chiari malformations were originally identified in the Cavalier King Charles Spaniel and, in general, are more common in small breed dogs. Other breeds affected with chiari-like malformations include the Affenpinscher, Boston terrier, Brussels Griffon, Chihuahua, French bulldog, Havanese, Maltese terrier, Miniature dachshund, Miniature pinscher, Papillon, Pekingese, Pomeranian, Pug, toy/miniature poodle, Shih tzu, Staffordshire Bull Terrier, and Yorkshire Terrier.

Various malformations can occur concurrently with CLM, such as hydrocephalus or an intracranial arachnoid cyst. Syringomyelia (SM) is an associated disorder primarily observed in Cavalier King Charles Spaniels and is the most commonly observed Chiari malformation 10. The increased popularity of this breed, along with increased availability of neurologic imaging techniques, has proven SM to be far more common than previously believed.

Pathologically, Syringomyelia is characterized by the presence of abnormal fluid-filled chambers within the cervical spinal cord (called “syrinxes”). As such, abnormal sensations and significant neck pain are the hallmark of this disease.

Clinical Signs of Syringomyelia

Clinicals signs vary depending on the severity of the problem in the individual dog.

Symptoms may include:

• Scratching at the neck or shoulders, sometimes referred to as phantom scratching. Some dogs will scratch while walking, which is believed to be due to phantom pain.
• As the condition progresses, clinical signs impacting the nervous system include:
  • Crying out when jumping up or running
  • Crying out during the night in pain
  • Loss of balance (ataxia)
  • Excessive rubbing of the face
  • Hearing loss
  • Neck pain
  • Pain when defecating (due to increased pressures in the skull and abdomen that occur with normal defecation)
  • Pain when held
  • Sensitivity when touched near the neck, head, shoulder, ear, and chest. This can include reluctance or sensitivity when wearing a collar.
  • Weakness
  • Withdrawn behavior (believed to be due to the fear of pain with handling)

Diagnosis

Age, breed, and clinical signs are generally considered sufficient evidence for a presumptive diagnosis. The general physical examination at the vet is typically normal. However, the neurologic exam (evaluation of the nervous system) can reveal a head tilt, nystagmus, loss of balance, poor coordination, trouble walking, tremors, and/or vision abnormalities. The most common observation with CLM is pain in the neck and head regions.

Diagnostic tests may include:

• Radiographs (X-rays) of the neck and skull can rule out fractures and some orthopedic problems, but are generally not helpful to diagnose this condition.
• A cerebral spinal fluid tap is commonly recommended to evaluate for other causes of symptoms, such as infections, inflammatory conditions, and/or cancer.
• Routine bloodwork is recommended, like a complete blood count (CBC), chemistry panel (biochemical profile), and urinalysis. These are conducted to rule out other underlying causes of the symptoms.
• Hearing tests, such as with the Brainstem auditory evoked response (BAER), may be recommended as hearing loss can develop in dogs with CLM.
• Definitive diagnosis, however, can only be achieved with advanced imaging via magnetic resonance imaging (MRI) of the skull and neck. The MRI can be helpful to evaluate the severity of the deformity. Abnormalities noted may include cerebellar herniation and bony compression of caudal cerebellum with medullary kinking.

Treatment of Chiari Malformation and Syringomyelia in Dogs

Treatment of chiari malformations can be difficult for severely affected dogs. The focus of treatment is on pain relief.

Treatment options include the following:

• Inflammation and Pain Control. For those mildly affected, medical management includes anti-inflammatory and pain medications with steroids (like prednisone), and pain control medications (like gabapentin), which has proven somewhat effective. Other pain medications such as tramadol, codeine, amantadine, and/or pregabalin may be considered. Acupuncture may be helpful for neuropathic pain. Routine reevaluation with your veterinarian is important as pain often progresses over time.
• Decreasing CSF Production. Drugs to decrease CSF production can be helpful in some dogs. Drugs used may include omeprazole, acetazolamide, and/or methazolamide.
• Comfort Care. Elevation of food and water bowls can decrease pain when eating and drinking. Avoid collars that put pressure on the neck and substitute with a harness when needed.
• Surgery. As the condition progresses and medical therapy becomes less successful, a surgical procedure called foramen magnum decompression may be effective in relieving pressure on the affected structures. Some dogs may receive a lifelong reprieve from symptoms after undergoing this highly-specialized procedure. The effectiveness of surgery is variable. Some dogs will improve, and then ultimately decline after 1 – 2 years.

Associated Veterinary Cost

Because definitive diagnosis for chiari-like malformation and syringomyelia requires a high-tech imaging technique, the cost of diagnosis can be prohibitive for many pet owners. Typical costs for magnetic resonance imaging ranges from $1,800 to $3,100. The cost of a cerebrospinal fluid tap, including procedure fee, anesthesia, and laboratory analysis, can be approximately $700 to $1900.

The cost of treatment depends greatly on the severity of the disease. If medical management is considered sufficient, expenses are likely to remain under $60 a month for drugs most commonly employed in these cases.

Surgical management is considered expensive. Estimates ranging from $5,000 to $10,000 are common.

Prognosis for Dog with Chiari Malformations

Medical therapy appears to help symptoms in most patients. There appears to be little correlation between the MRI findings and the severity of the symptoms. Surgery is recommended and success rates range from 50% to 80%. Repeat surgery may be needed in certain cases.

Prevention

Sadly, this disease is considered highly preventable via sound breeding practices. Terminating all breeding lines bearing any afflicted offspring is the ideal approach to eliminating this disease. A resource for breeders can be found here.