Chiari-like malformation and Syringomyelia
Often referred to as Chiari-like malformation or caudal occipital malformation syndrome, syringomyelia (or syringohydromyelia) is a condition that is commonly seen in dogs. Dogs with this condition develop a cyst-like lesion in their spinal cord, causing pain and movement problems. There is a genetic predisposition for this neurological disorder in Cavalier King Charles Spaniels (CKCS), but it can also occur in other breeds such as the Affenpinscher, Boston Terrier, Chihuahua, French Bulldog, Griffon Bruxellois, King Charles Spaniel, Maltese, Papillon, Pomeranian, Pug, and Yorkshire Terrier). Now that MRIs are readily available for veterinary patients, the diagnosis of syringomyelia can be easily confirmed.
What is syringomyelia?
A fluid known as cerebrospinal fluid (CSF) bathes the brain and spinal cord of dogs. Syringomyelia refers to a condition in which the spinal cord has one or more cavities filled with fluid (singular: syrinx, plural: syringes). There is an unusual conformation of the back of the skull in CKCS (Chiari-like malformation), which makes them especially susceptible to developing a spinal cord cavity.
Conformational abnormalities limit the space available for the cerebellum to develop inside the skull (occipital bone). As a result, the cerebellum is forced through the opening at the base of the skull (where the spinal cord exits). CSF flows abnormally from the brain to the spinal cord as a result of this pressure point. A syrinx can form over time as a result of this flow disturbance.
As a result of the dilated fluid area damaging spinal cord cells, the nerve signals from the neck are distorted. This condition can cause a variety of signs in pets. It is quite common for the signs to be mild. In more severe cases, weakness and wobbliness may occur. There may be abnormal pain sensations (such as itchiness, hot and cold flushes, and pins and needles); there may be abnormal muscle posture, resulting in a head tilt or scoliosis.
What causes syringomyelia?
In the nervous system, spinal fluid nourishes and removes waste from the brain and spinal cord. Upon exiting the head, the fluid travels along the spine and is slowly reabsorbed. Syrinxes are fluid pockets formed in the spinal fluid system by abnormal flow, usually caused by flow obstructions or flow changes.
In most cases, the obstruction is caused by a congenital (from birth) malformation of the skull called a ‘Chiari-like malformation’, which alters the flow of spinal fluid. Chiari-like malformation refers to a condition where the brain (too large) and skull (too short) have an abnormal conformation. Due to this mismatch in size, the back part of the brain is compressed into the opening at the back of the skull, obstructing the flow of cerebrospinal fluid. Many cavalier king Charles spaniels and other small breed dogs have this malformation, which may not cause clinical signs; it can often be considered coincidental.
If a pet is diagnosed with syringomyelia, it is important to understand whether the diagnosis is clinically significant or not.
What are the signs of syringomyelia?
The severity of syringomyelia does not appear to be related to the severity of clinical signs between dogs.
A yelp or other spontaneous vocalization is by far the most common clinical sign of syringomyelia, as is pain expressed when moving or being lifted, or reluctance to exercise. Dogs may scratch their necks without making contact, rub their faces repeatedly, or lick their paws excessively in an effort to relieve discomfort. We cannot always tell what our pets are feeling, and some dogs may display these signs for completely unrelated conditions like flea allergies or ear infections.
The disease may also cause twisting of the neck (scoliosis), stiffness in the front limbs, muscle loss in the neck, and weakness or lameness in the front legs. Signs usually appear before 6 years of age and worsen as the dog gets older. Puppies as young as 12 weeks have been reported with the condition.
Syringomyelia can be detected on MRI even in dogs without any clinical signs, and similar clinical signs may be seen in dogs with other neurological disorders.
How do I diagnose syringomyelia?
MRI scanning is the best way to diagnose syringomyelia. CT scans (which focus more on bones) are good for detecting abnormal bone conformation in the skull, but MRIs are best for detecting brain and spinal cord abnormalities.
Can syringomyelia be treated?
Syringomyelia can affect many dogs, though certain activities may cause additional pain (e.g. stroking the neck, rubbing the ears, eating from the ground, etc.) and should be avoided where possible.
Currently, there is no cure for dogs with syringomyelia. Medical and surgical treatments have been tried, but surgical correction is the best option for people. The first line of treatment for neurological signs in dogs is usually medical management depending on the severity and age of the patient.
Typically, anti-inflammatory drugs, gabapentin, or prednisolone are used to treat the condition. Syrinx inflammation can be reduced with anti-inflammatory drugs. In dogs and humans, gabapentin is used to treat pain caused by neurological diseases as well as abnormal sensations (like pins and needles). The last resort is corticosteroids (prednisolone) which reduce CSF production as well as inflammation. In the event that none of the drugs work, a surgical procedure may be considered.
There have been reports of surgeries that enlarge the hole at the base of the skull in order to relieve pressure and restore a normal flow of CSF between the brain and the spinal cord. This surgery aims to reduce the pressure on the skull base to allow fluid to flow normally. A few studies suggest that the syringes may resolve after this procedure. Surgery, however, is not shown to be a better long-term treatment option than medical therapy, so it is reserved for patients with severe and progressive signs.
In most cases, medical treatment will be able to control these signs; however, it is a chronic disease and treatment may be required for life. The treatment aims to reduce the pain and inflammation caused by the formation of a syrinx.
What will happen to my dog if it has syringomyelia?
In general, this condition has a good prognosis. The most common reason for this is that most patients respond well to treatment, and it is very often possible to withdraw treatment over time. When the inflammatory and formation phases of a syrinx have finished, a patient may return to normal.
The course of treatment may require occasional visits to the practice as flares up do occur. To assess whether treatment is having an effect on organ function, it is important to perform blood tests every few months.