Chiari Malformations

Patty Khuly

Summary

Chiari malformations (also referred to as “Chiari-like malformations”) 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.

While our understanding is limited when it comes to knowing exactly how these diseases states arise, conformational deformities of the foramen magnum (the site through which the brainstem passes) and a subsequent crowding of the sensitive neurologic structures located here have been implicated.

Once considered rare, the increased popularity of Cavalier King Charles Spaniels, along with the increased availability of neurologic imaging techniques, has led us to deem the condition far more common than we formerly believed.

Syringomyelia, observed primarily in Cavalier King Charles Spaniels, is the most common Chiari malformation observed. This condition is characterized pathologically by the presence of abnormal fluid-filled chambers within the cervical spinal cord (called “syrinxes”). As such, significant neck pain is the hallmark of this disease.

Recently, it’s been determined that cats can also be affected.

Symptoms and Identification

The most common clinical sign initially observed in Chiari malformation patients is scratching at the neck or shoulders. As the condition progresses, loss of balance (ataxia), weakness, and neck pain may develop.

Age, breed, and symptoms are generally considered sufficient evidence for a presumptive diagnosis. Definitive diagnosis, however, can only be achieved via MRI of the skull and neck.

Affected Breeds

Chiari malformations were originally identified in the Cavalier King Charles Spaniel. However, they have since been recognized in many different breeds of dogs –– in particular, the Brussels Griffon, among other toy breeds.

Treatment

Treatment of Chiari malformations is difficult for severely affected patients. For those more mildly affected, medical treatment with steroids (like prednisone) and/or gabapentin has proven somewhat effective –– at least initially.

As the condition progresses, a procedure called foramen magnum decompression may be effective in relieving the pressure on the affected structures. Some patients may receive a lifelong reprieve from symptoms after undergoing this highly specialized procedure.

Veterinary Cost

Because definitive diagnosis requires a high tech imaging technique, the cost of diagnosis can be prohibitive for many pet owners. Typical costs for an MRI range anywhere from $1,000 to $2,000.

The cost of treatment depends greatly on the severity of the disease. If medical management is considered sufficient, expenses are likely to remain under $50 a month for the drugs most commonly employed in these cases.

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

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.



References

Couturier J, Rault D, Cauzinille L. J Small Anim Pract. Chiari-like malformation and syringomyelia in normal cavalier King Charles spaniels: a multiple diagnostic imaging approach. J Small Anim Pract. 2008 Sep; 49(9):438-43. Epub 2008 Jul 10.

Park C, Kang BT, Yoo JH, Park HM. Syringomyelia in three small breed dogs secondary to Chiari-like malformation: clinical and diagnostic findings. J Vet Sci. 2009 Dec; 10(4):365-7.

Rusbridge C, Greitz D, Iskandar BJ. Syringomyelia: current concepts in pathogenesis, diagnosis, and treatment. J Vet Intern Med. 2006 May-Jun; 20(3):469-79.

Wolfe KC, Poma R. Syringomyelia in the Cavalier King Charles spaniel (CKCS) dog. Can Vet J. 2010 Jan; 51(1):95-102.