Caudal Occipital Malformation Syndrome
Caudal occipital malformation syndrome (COMS) is a condition in dogs which resembles Chiari malformation of people. COMS is a congenital disorder in which the back of the skull forms incorrectly, leading to compression of the cerebellum (the back of the brain) and abnormal flow of fluid from the skull to the vertebral column. The compression and abnormal fluid dynamics result in dysfunction of neurons in the brain and spinal cord.
Small breed dogs are most commonly affected by COMS, with the Cavalier King Charles Spaniel at highest risk. While COMS is a congenital disorder, meaning it is present at birth, clinical signs of the disease typically don’t appear until a few years of age. These signs may include neck and/or head pain, dizziness/falling, difficulty walking, limb weakness, and scratching at the neck.
An MRI is required to diagnose the structural abnormalities characteristic of COMS. Following diagnosis, there are two arms of treatment to consider:
1. Medical treatment to reduce fluid production in the brain and to decrease pain associated with COMS. Drugs commonly used to decrease fluid production include omeprazole and prednisone. For pain relief, gabapentin and tramadol are two potentially useful medications. While medications can control dogs who have mild clinical signs of COMS, those cases with moderate to severe signs often do not achieve adequate relief with medical management alone.
2. Surgical treatment is indicated for dogs who do not achieve a good quality of life with medical management. The aim of surgery is to relieve brain compression and to restore normal fluid dynamics.
Foramen magnum decompression, the surgery used to treat COMS, has a success rate of 80%. Amongst these successes, however, 1/3 will have a recurrence of clinical signs months to years later which may require a second surgery.
If you or your veterinarian is concerned that your dog has signs of COMS, you may schedule a consultation with our neurologist, Dr. Jones, at 804-784-8722 to discuss this condition and its treatment further.