other names: caudal occipital malformation syndrome, COMS
Overview
Chiari-like Malformation (CM) is a condition resulting in a mismatch between the size of the back part of the skull and the amount of brain tissue it contains. In a very general sense, the size of the skull is too small for the brain, which results in compression of the back part of the brain. Although CM itself does not typically cause direct clinical signs, it often leads to a secondary condition called syringoydromyelia (SM) due to the way it alters the normal flow of cerebrospinal fluid (CSF) as it exits the skull.
Syringohydromyelia is a condition in which a fluid-filled cavity, called a syrinx, develops within the spinal cord. The size and severity of the syrinx can vary widely and may lead to a range of neurological signs.
Causes
Chiari-like malformation is a condition present from birth and is thought to be inherited, meaning genetics likely play a role in its development. CM is most commonly seen in Cavalier King Charles Spaniels, Brussels Griffons, Chihuahuas, and French Bulldogs
Clinical Signs
Dogs affected by this condition most commonly experience episodic pain, which is typically focused around the neck and shoulders. One of the most distinctive signs is phantom scratching, where the dog repeatedly scratches at the air or the side of its body without ever actually making contact with the skin. In some cases, affected dogs may also develop an abnormal curvature of the spine or show signs of weakness or difficulty walking.
It’s important to note that many dogs with Chiari-like malformation and syringohydromyelia show few or no clinical signs at all.
Diagnosis
The definitive diagnosis of Chiari-like malformation and syringohydromyelia is made using an MRI. An MRI can show the compression at the back of the brain and whether a fluid-filled cavity (SM) has developed within the spinal cord.
Because CM can sometimes occur without causing a clinical problem, and because the severity of neurologic signs does not always match the severity of MRI findings, diagnosis and treatment decisions are based on both the imaging results and the dog’s symptoms. Additional tests such as cerebrospinal fluid (CSF) analysis may be performed to rule out other neurologic diseases, especially if infection or inflammation is suspected.
Treatment
Medical management of CM focuses on relieving discomfort and slowing the progression of clinical signs. Medications commonly used include pain relievers such as gabapentin, pregabalin or amantadine, which help manage nerve-related pain. Anti-inflammatory steroids may be used to reduce inflammation and help decrease cerebrospinal fluid (CSF) production. Depending on the individual dog, these medications may be needed either short-term or long-term. Omeprazole is another medication that can be prescribed to reduce CSF production, though its effectiveness is still uncertain.
This approach can be quite effective for dogs showing mild clinical signs, helping to improve comfort and quality of life. However, it’s important to understand that CM is often a progressive condition, and clinical signs can worsen over time and medication adjustments may be needed.
In cases where signs are more severe or progressing discomfort, surgical treatment may be recommended. The most commonly performed procedure is called a foramen magnum decompression, in which a portion of bone is removed from the back of the skull to relieve compression and restore more normal CSF flow. While this does not cure the condition entirely, it may slow progression and significantly improve symptoms in some patients. However, even after a successful surgery, it is possible for some dogs to experience a recurrence of symptoms, and they may still require ongoing medical management to maintain an adequate quality of life.
As part of a complementary approach, acupuncture can be helpful for managing discomfort. Additionally, dogs with Chiari-like malformation and syringohydromyelia should always be walked using a chest harness to avoid putting pressure on the neck.
Prognosis
The prognosis for dogs with Chiari-like malformation and syringohydromyelia can vary widely depending on the severity of the condition, although generally the prognosis is fair to good. Dogs with mild symptoms and those who respond well to medical management can enjoy a good quality of life and have a favorable long-term outlook.
In dogs with severe pain or significant neurological deficits, the prognosis is more guarded. In these cases, managing the condition becomes more challenging, and the response to treatment can be less predictable.