Clinical Investigation

Caudal Occipital Malformation Syndrome (COMS)/

Canine Chiari Malformation Project

The Chiari/COMS project at LIVS is designed to provide information that will be useful in identifying the degree of risk in those dogs likely to manifest symptoms of caudal occipital malformation syndrome.

CHIARI MALFORMATION

The Chiari malformation in humans and the Chiari-like malformation in dogs (CM), also known as Caudal Occipital Malformation Syndrome (COMS), is a condition where part of the brain, the cerebellum, descends out of the skull, through the opening at its base, putting pressure on the spinal cord. It is considered to be a developmental abnormality; therefore it affects both children and puppies during the growing years.

Because of an overly small skull and the resultant pressure on the spinal cord, the normal cerebral spinal fluid flow (CSF) is disrupted. The abnormal flow of CSF results in extreme pressure gradients causing the formation of fluid accumulations within the spinal cord each of which is called a syrinx. It is both compression of the cerebellum and the formation of the syrinxes that cause the various clinical signs seen in puppies and children. In some patients, the central canal of the spinal cord is only slightly dilated referred to as hydromyelia. In cases where the dilation is greater than 2mm and fluid leaks into the spinal cord, it is called syringohydromyelia or simply syringomyelia (SM).

The focus is now on correcting the flow of CSF as the malformation results in the secondary condition known as syringomyelia. Syrinxes exert pressure on the spinal cord, compressing and stretching its fibers and in some cases permanent nerve damage and paralysis results. The clinical condition in dogs has been recently described, with many of the early reports originating from the Surgery Department at Long Island Veterinary Specialists (LIVS), and appears analogous to the Chiari type I malformation in humans. It is recognized in small breed dogs (dogs under 30 pounds), mostly found in Cavalier King Charles Spaniels. Here too there is strong evidence that it is a heritable condition.

Clinical signs of CM & SM are usually recognized between 6 months and 3 years of age. In addition to signs of neck pain, affected dogs frequently scratch at the neck or shoulder region, have weakness in the fore or rear limbs and can seizure. In the CKCS breed, it is estimated that 95% have the Chiari malformation and as many as 50% have both Chiari and syringomyelia.

Breeds of dogs treated at LIVS so far have been the Cavalier King Charles Spaniel, King Charles Spaniel, Yorkshire Terrier, Maltese Terrier, Chihuahua, Miniature Dachshund, Toy Poodle, Bichon Frise, Pug, Shih Tzu, Pomeranian, Boston Terrier, Pekingese, and the Miniature Pinscher. The CKCS is a relatively modern breed of dog developed in the 1920’s and its friendly disposition and attractiveness made it very popular among toy breeds. Although hereditary mitral valve lesions and ocular disorders have been reduced by selective breeding, newer breeding recommendations are under investigation at this time.

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The diagnosis of CM &SM in dogs can only be confirmed by MRI which is essential for the detection of syringomyelia. Studies at LIVS suggest less involved screening tests like the Brain Auditory Evoked Response (BAER test) may be helpful in screening patients in the future. Current diagnostics like Spiral CT and Thermography are under investigation for their usefulness in screening dogs at LIVS.

Medical treatment is directed towards pain relief and the reduction of CSF production. The most frequently prescribed medications are furosemide, non steroidal anti-inflammatory drugs, corticosteroids, carbonic anhydrase inhibitors and treatments utilizing acupuncture. The long term prognosis for patients treated medically is poor, since the underlying condition remains unaddressed.

The preferred management of Chiari I malformation in human patients is Foramen Magnum Decompression (FMD) and recent studies in dogs suggest that the same procedure is effective treatment for CM &SM, especially if performed early in the disease course. Unfortunately without benefit of surgery, 36% are euthanized for uncontrolled pain. In both human patients and dogs, approximately 25-30% of patients having FMD will have recurrence of clinical signs due to scar tissue formation at the surgical site within 6 months of surgery.

The goal of surgery is to decompress the occipital area, in other words to “make room for the cerebellum”, reducing the pressure, restoring normal CSF flow dynamics and allowing the syrinx to shrink. The procedure has two parts. The first is to remove a piece of the skull bone which surrounds the cerebellum called FMD. The second is to affix a titanium mesh with small screws to cover the exposed cerebellum referred to as cranioplasty. In a recent study of 28 dogs followed greater than 8 months after undergoing this procedure, 91% of dogs improved post-operatively and none formed scar tissue at the surgical site requiring re-operation. Although surgery is not a complete solution to the disorder, the FMD with cranioplasty procedure was well tolerated and significantly improved the quality of life in almost all of the dogs on whom the procedure was performed.

The surgical technique of FMD with cranioplasty was pioneered at LIVS by Dr. Curtis Dewey and Dr. Dominic J. Marino and is the most promising treatment option so far. This technique is performed at few facilities world wide at this time. Familiarity with this technique and the promising results achieved at LIVS is not widespread at this time. Questions about the diagnosis and treatment options for patients suspected of having CM & SM should be directed to the neurosurgeons at LIVS.

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FREQUENTLY ASKED QUESTIONS

What is Chiari / Caudal Occipital Malformation Syndrome (COMS)?

Chiari malformation refers to a developmental abnormality of the posterior fossa in humans resulting in compression of the cervicomedullary junction with tonsuillar herniation and secondary alterations in cerebrospinal fluid (CSF) dynamics. Neurologic manifestations may be the result of direct compression of nervous tissue by osseous or meningeal tissues or the result of alterations in CSF dynamics. With the more frequent use of MRI in veterinary medicine, recent identification of the canine counterpart, caudal occipital malformation syndrome (COMS), has lead to the recognition of several neurologic manifestations in canine patients attributable to this malformation and the secondary alterations in CSF dynamics.

How is COMS identified in canine patients?

Magnetic resonance imaging (MRI) is the only imaging modality to date, that can definitively identify this condition in veterinary patients. Because anesthesia is required to perform MRI in veterinary patients, there are increased costs and risks associated with this modality. Additionally, limited availability has lead to evaluation of alternate methods of screening or identification this condition. Preliminary results of less invasive modalities being evaluated as screening diagnostics such as brain stem auditory evoked response (BAER)and thermal imaging (TI) are being evaluated at Long Island Veterinary Specialists. Normal Brain-sagittal view

What kind of treatment is available once a diagnosis has been made?

Foramen magnum decompression (FMD) is the preferred mode of therapy in both human and veterinary patients; however, approximately 25% of both types of patients require additional surgery due to excessive scar formation. A cranioplasty procedure for dogs was developed at Long Island Veterinary Specialists, based on a technique used at The Chiari Institute, Great Neck, NY. Results of our ongoing study have COMS brain-sagittal view been very promising and will be published soon.

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STUDY PROTOCOL

Low cost screening of COMS (Chiari malformation) is being offered at LIVS. This program for breeders ($500. per dog in groups of 3) includes a neruological evaluation, a Spiral CT scan, an MRI, BAER testing and a Thermography scan. Copies and/or reports of any previously performed MRI's should be brought in at time of screening.

An additional charge will be levied for needed medications, tests and requested copies of MRI's and CT scans. Post-op crainioplasty front view

Initial results of the screening tests will be presented orally, before discharge by a member of the Surgery/Neurology department. Written discharge instructions will be given as well. When grading scale has been finalized in 6-8 weeks by Dr. Dominic J. Marino, in conjunction with Dr. Clare Rusbridge, a written summary will follow. Breeding recommendations will then be offered based on a protocol devised by Dr. Rusbridge depending on grading results.

Contact Alexis Bomzer at:

516-501-1700, ext. 267 to schedule appointments.

Arrival time for screening is 7:30 am. Release time is between 12 noon and 5:00 pm

the following day.

Please submit the completed questionnaire at time of admission.(see below)

Dogs will not be shaved.

Checks are not accepted- cash or credit cards only, please.