Caudal occipital malformation syndrome is a disease that looks like type 1 Chiari malformation in humans. It is a congenital malformation (present since birth) most probably of genetic origin which affects the back portion of the skull and which leads to the compression of the neurological structures in this area. Essentially, it is the brain that is too big with respect to the skull. The lack of space then forces the cerebellum and the brainstem (two structures that form the brain) to exit the foramen magnum (opening in the skull through which the spinal cord passes). When pockets of liquid form in the spinal cord, we are talking about syringomelia.
It is small breed dogs that are affected by this syndrome, in particular the Cavalier King Charles Spaniel, the Brussels Griffon, the Maltese Bichon, the Yorkshire, the Chihuahua and the miniature versions of other breeds. The signs appear between 5 months and middle age, without predisposition to sex or color.
The main symptom consists of pain caused by the obstruction due to the pulsing surge of cephalorachidian fluid and/or by the damage to the nervous paths of the spine. Therefore we can observe a dog who keeps his distance and who cries out when he jumps, gets excited, defecates or is picked up. The pain is often intermittent and worse at night. He may show sensitivity or scratch his shoulder, neck, ear or sternum. He may rub his face or ear. He might scratch himself while walking without coming into contact with the skin. This behavior may be triggered by a collar, a touch, a movement or excitement.
Some animals will suffer from concurrent convulsions although a direct link has not been proven. The Cavalier King Charles Spaniel also often suffers from concurrent deafness but again, a direct link has not been established.
The physical examination may be normal or reveal back pain of variable intensity. The dog may be sensitive to touch, especially around the ears, paws, sternum and neck. In severe cases, we may observe a deviation in the spinal cord at the junction between the neck and back, a shaky gait as well as weakness.
The best method for diagnosing the condition is through magnetic resonance. Generally we will observe the displacement of the cerebellum and the medulla in the foramen magnum with very little or no cephalorachidian fluid around the neural structures. If there is the presence of syringomelia, then we will find cavities filled with liquid in the cervical region of the spinal cord.
The main objective of treatment consists of easing the pain. Surgery is the best option for long term success but the condition deteriorates just the same in about 50% of cases around two and a half years following the surgery. The surgery consists of removing a piece of the bone to decompress the foramen magnum and by doing so, reestablish the normal flow of cephalorachidian fluid.
Initially, we must often rely on treatment with medication. We can use medication which serves to reduce the pressure of the cephalorachidian fluid such as diuretics which increase the production of urine or antacids which reduce gastric acid.
If following a treatment like this, the animal is more comfortable then we can reconsider surgery. When the pain remains as intense we can add or change for a non-steroid anti-inflammatory. If the response is still not adequate then we can add a neurogenic analgesic. Finally, the last option consists of using steroid anti-inflammatories such as cortisone.
It will be important to reexamine the animal at 1 to 3 month intervals to determine if the control of pain is adequate as well as to evaluate his neurological state. It is not necessary to reduce the level of exercise but the dog may himself avoid certain activities. Furthermore, he may not tolerate grooming.
We can also help by placing the food bowls higher up and use a harness instead of a collar.
The progression of the affliction is variable. Some dogs remain stable or deteriorate very little over the years. Others will develop an elevated level of pain or neurological deficits in the months following the first appearance of symptoms.
It is preferable to do periodic blood testing if the animal is receiving medication in order to detect any negative effects to the internal organs.