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Caudal Occipital Malformation Syndrome (COMS/SM)

WHAT IS Caudal Occipital Malformation Syndrome/Syringomyelia (aka Chiari-like Malformation)?


What we have commonly referred to as CM (Chiari Malformation) and SM (Syringomyelia) is now also being classified as COMS (Caudal Occipital Malformation Syndrome), a more blanketed term to include these main attributes of the disease.


COMS occurs when there is not enough room in the skull for the back portion of the brain. As a consequence, the cerebellum is pushed from its normal position to protrude through the skull base, causing spinal fluid to flow abnormally,  leading to fluid build up in the spinal cord (called syringomyelia or SM).

drawing of comparison of the brain of a normal cavalier king charles spaniel and one with chiari malformation

Figure 1

 Up to 95% of Cavalier King Charles Spaniels have the malformation, while a much smaller percentage have actual symptoms. Symptoms include: Scratching at the neck and ears, often with a non-contact scratching motion referred to as “phantom scratching”; Head and Neck Pain; Incoordination and weakness; Abnormal curvature of the neck (Scoliosis); and less commonly, seizures, facial paralysis, and deafness have been reported. The disease, although most diagnosed in young adult Cavalier King Charles Spaniels, can be found in any age and many other small breeds as well.


To acquire a true diagnosis for COMS/SM an MRI of the brain and spinal cord must be conducted. However, most cases of mild forms of the disease are diagnosed through presenting symptoms. Due to the expense, an MRI is usually reserved for cases with moderate to severe symptoms.


There are medical and surgical treatments for COMS/SM. The first course of action is most commonly to begin with medications aimed at reducing the amount of spinal fluid and treating symptoms like pain and seizures. In mild to (some) moderate affected dogs, the medicines may work for several years. Unfortunately, medications do not fix the underlying problem and in many dogs, they become less and less effective over time until they no longer provide any comfort. The most common medications used are:


Gabapentin – To treat pain and abnormal sensations such as tingling and burning. If this medication is not successful, other medications like pregabalin or amantadine may be prescribed.

Prednisone (or other steroids) – To help reduce the production of spinal fluid in the brain and reduce inflammation.

Omeprazole – To reduce the production of spinal fluid in the brain and can help with the GI upset that develops secondary to prednisone.

Tramadol – To treat pain and discomfort.

Seizure Medications – These may also need to be prescribed.


Sometimes, when qualifying factors are met, more severely affected patients that do not respond well to medications can be surgery candidates. At surgery, the abnormal piece of bone that is pinching the brain is removed to allow the spinal fluid to flow more naturally. Depending on the exact nature of malformation, a neurologist may recommend placing a shunt to drain excess fluid from the brain. An improvement in approximately 80% of dogs is seen with surgery. Some dogs will still require some medications after surgery, but usually in much lower doses.



There is a congenital ear problem found primarily in Cavaliers that can mimic many of the symptoms of COMS/SM, including scratching, as well as head and neck pain. With this disease there is a buildup of mucus without signs of infection deep in the ear, which stretches the eardrum causing pain. It is also diagnosed via MRI/CT scan. Treatment involves draining the mucus by a variety of methods. Because the symptoms are so similar, it should be considered when discussing COMS/SM to be certain when a Cavalier is presenting with symptoms that they are treated for the correct disease.

Author: Angela Schuller

Disclaimer: As a breeder who cares deeply for my dogs and puppies I act as responsibly as I can.  The information provided is intended to inform and help to lessen the alarm when COMS/SM becomes a topic with your veterinarian. Ultimately, once a puppy leaves my home relinquished to an owner's care, owners must then take on the responsibility for their decisions. As always, if your pet has an urgent medical concern, please consult your veterinarian. Finally, as your trusted breeder, I am always available to offer support and answer questions. 


Cavalier Health Website,

“Figure 1”, David Brewer DVM, DACVIM (Neurology), Accessed 22  July 2023

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