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Syringomyelia (SM) in the Cavalier King Charles Spaniel

Also check out our expanded version about  Cavalier King Charles Spaniels on our blog.

Source: Thank you to cavalierhealth.org for this very helpful information.  Please visit cavalierhealth.org/syringomyelia.htm for complete information, studies, and treatment options.

What is Syringomyelia

Syringomyelia (SM), also known as syrinx and hydromyelia, and occasionally mis-identified as Arnold Chiari malformation) is a condition of the development of fluid-filled cavities in the spinal cord, which is believed by researchers to be due to abnormal flow of cerebrospinal fluid (CSF) between the brain and the spinal cord through the foramen magnum at the base of the skull.

SM was first identified by veterinary neurologists in the late 1990s, while classic symptoms, such as air scratching, had been reported anecdotally prior to then.

Syringomyelia in Cavalier King Charles Spaniel
Syringomyelia in Cavalier King Charles Spaniel

Technically, hydromyelia is a dilatation of the central canal within the spinal cord, and syringomyelia is the cavitation of the spinal cord parenchyma.  Combined, they are referred to either as syringo-hydromyelia (SHM) or hydro-syringomyelia.  The disease is referred to generally as syringomyelia and SM herein.  This condition is similar, but not identical, to Arnold Chiari Type I Syndrome in humans.

Photo shows how the position of the brainstem was evaluated by measuring the distance between the obex (the caudodorsal-most border of the fourth ventricle) and a line drawn parallel to the foramen magnum. This was termed the "obex measurement
Photo shows how the position of the brainstem was evaluated by measuring the distance between the obex (the caudodorsal-most border of the fourth ventricle) and a line drawn parallel to the foramen magnum. This was termed the “obex measurement.

rusbridge-mri-ckcs-with_notes[1]

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Syringomyelia also may be described as syringomyelia secondary to Chiari-like malformation (CM or CLM). CM is also referred to as occipital hypoplasia (OH) or caudal occipital malformation syndrome (COMS).  The full relationship between CM and the development of SM is not fully understood.

The atlas is the spinal vertebra (C1) closest to the skull. It sits next to the foramen magnum, the hole in the occipital bone. The "atlanto-occipital joint" is the connection between the atlas and the occipital bone, and is stabilized by ligaments. "Atlanto-occipital overlapping" (AOO) is characterized by a decreased distance between the atlas and the occipital bone. In some cases, the dorsal arch of the atlas may actually protrude into the foramen magnum. See the image (courtesy of: www.wikispaces.com).
The atlas is the spinal vertebra (C1) closest to the skull. It sits next to the foramen magnum, the hole in the occipital bone. The “atlanto-occipital joint” is the connection between the atlas and the occipital bone, and is stabilized by ligaments. “Atlanto-occipital overlapping” (AOO) is characterized by a decreased distance between the atlas and the occipital bone. In some cases, the dorsal arch of the atlas may actually protrude into the foramen magnum. See the image (courtesy of: www.wikispaces.com).

SM is rare in most breeds but reportedly has become very widespread in cavalier King Charles spaniels and the Brussels Griffon (Griffon Bruxellois).  Some researchers estimate that as many as 95% of CKCSs may have Chiari-like malformation (CM or CLM), the skull bone malformation believed to be a part of the cause of syringomyelia, and that more than 50% of cavaliers may have SM.* It is worldwide in scope and not limited to any country, breeding line, or kennel, and experts report that it is believed to be inherited in the cavalier King Charles spaniel. CM is so widespread in the cavalier that it may be an inherent part of the CKCS’s breed standard.

A 2011 study of 555 UK cavaliers, reported by their owners to be symptom-less, found 25% of one year olds and 70% of 6+ year olds had SM. However, in a 2015 study of the veterinary records of 3,860 CKCSs in the UK and Australia from 2009 to 2014, only 37 were diagnosed by MRI as being affected with CM/SM and an additional 84 cavaliers were suspected of being affected.

The severity and extent of syringomyelia also appear to get worse in each succeeding generation of cavaliers. Other breeds known to be affected to a lesser extent include the Affenpinscher,Bichon Frisé, Boston terrier, bull terrier, Chihuahua, French bulldog, Havanese, King Charles spaniel (the English toy spaniel), Maltese terrier, miniature dachshunds, miniature and toy poodles, Papillon, Pomeranian, Pugs, Shih Tzu, Staffordshire bull terrier, and the Yorkshire terrier.

Symptoms

Phantom Scratching
Symptoms may vary widely among different dogs, but the earliest sign often is that the dog feels a sensitivity in its neck area, causing in some an uncontrollable urge to scratch at its neck and shoulders excessively, particularly when walking or during other forms of exercise, and usually without making skin contact (phantom scratching).  This had been believed to be due to an increase in the pressure of the flow of cerebrospinal fluid through the central canal from the brain down the spinal column, causing the central canal to expand and press against the nerves of the spinal column and creating a pins-and-needle-like tingling or a burning-type pain, and other strange sensations (called dysaesthesia), which prompt the dog to scratch.

Pain
As the disorder progresses, there usually follows increasingly severe pain around the dog’s head, neck, and shoulders, causing it yelp or scream.* It is believed to be a neuropathic pain, probably due to disordered neural processing in the damaged dorsal horn.

In a 2009 study of 64 cavaliers affected with CM/SM, Drs. Sofia Cerda-Gonzalez, Natasha J. Olby and others classified clinical signs of pain from grade 0 to grade 5, by which the dogs displayed symptoms of neck scratching, head scratching, neck pain upon neurolgoical examination, as well as ataxia and paresis detected upon examination.
In a 2009 study of 64 cavaliers affected with CM/SM, Drs. Sofia Cerda-Gonzalez, Natasha J. Olby and others classified clinical signs of pain from grade 0 to grade 5, by which the dogs displayed symptoms of neck scratching, head scratching, neck pain upon neurolgoical examination, as well as ataxia and paresis detected upon examination.

sherritt_pain_score_scheme[1]

PSOM
Another disorder common to cavaliers and with symptoms similar to SM is Primary Secretory Otitis Media (PSOM), which is a highly viscous mucus plug which fills the middle ear and causes the tympanic membrane to bulge.  Because the pain and other sensations in the head and neck areas, resulting from PSOM, are so similar to symptoms due to SM, the possibility that the cavalier has PSOM and not SM should be determined before diagnosing SM.

Syringomyelia Diagnosis

MRI
The only accurate way of diagnosing the disease is said to be through the use of magnetic resonance imaging (MRI) scanning.  Clinic charges for MRI examinations of canines have been known to vary from $400.00 to over $2,000.00.*   Accurate MRI results require that usually the dog be anesthetized.  In view of the high cost of MRI scans, the examing veterinary specialist usually will attempt to rule out other causes of the symptoms first. Veterinarians who perform MRIs of should consider following this MRI Screening Protocol devised by Dr. Rusbridge.

Syringomyelia Treatment Options Diagram

Treatment options for CM/SM are very limited. However, some medications have been effective in some cases.

Drugs

Anticonvulsants
Anticonvulsants, such as gabapentin (Neurontin, Gabarone), have been successful in relieving neuropathic pain, which is evidenced by behaviors such as sensitivity to touch or phantom scratching. Gabapentin works through a receptor on the membranes of brain and peripheral nerve cells.  It binds tocalcium channels and modulates calcium influx as well as influences GABergic neurotransmission.  Its effect is to deaden the irritated nerve impulses in the dog’s neck.  A newer anticonvulsant, pregabalin (Lyrica), is being prescribed by some neurologists in treating SM.  It is closely related to gabapentin and was developed by Pfizer, which also developed gabapentin. Pfizer reports that pregabalin is more potent than gabapentin and achieves its effect at lower doses.  Doses of pregabalin also reportedly  have a longer lasting effect than gabapentin. No generic version is available, and as an exclusive brand, Lyrica is quite expensive in comparison to generic gabapentin.

Amitriptyline (Elavil, Tryptizol, Laroxyl, Sarotex) is a tricyclic antidepressant (TCA) by Merck which may be prescribed as an alternative to either gabapentin or pregabalin.

Zonisamide (Zonegram) is an anticonvulsant which in clinical trials appears to be effective for generalized seizures in dogs. It’s anti-seizure effect is believed to work through sodium and calcium channels.  Dr. Curtis Dewey has conducted studies of this drug.

Levetiracetam (Keppra) is an anticonvulsant which can also be used in conjunction with phenobarbital and/or potassium bromide. it appears to be relatively safe for dogs, and reportedly rarely has any adverse side effects and does not appear to affect the liver or liver enzymes.

Oral opioids (pethidine, methadone, tramadol) are alternatives to anticonvulsants.  Methylsulfonyl-methane (MSM) is recommended by some veterinary neurologists as a dietary supplement.

Non-steroidal anti-inflammatory drugs
The use of non-steroidal anti-inflammatory drugs (NSAIDs), such as carprofen* (Rimadyl, Quellin),meloxicam (Metacam), firocoxib (Previcox), mavacoxib (Trocoxil), and aspirin, may relieve the symptoms of non-neuropathic pain, such as is caused by the Chiari-like malformation rather than from the syringomyelia, as evidenced by yelping when either being picked up of changing posture. These drugs do not retard deterioration due to progression of the SM.

*Carprofen (Rimadyl, Quellin) may have serious side effects and should not be given without a veterinarian’s close guidance and monitoring.

It has been reported that SM-affected cavaliers have been found to have a high level of inflammatory proteins in their bodies, and that for that reason, NSAIDs often provide some initial relief from pain. Also, doxycycline, a tetracycline antibiotic designed to treat bacterial infections, has been prescribed to CM/SM patients as an anti-inflammatory similar to NSAIDs.

Proton pump inhibitors
Drugs which reduce the production of cerebrospinal fluid, including proton pump inhibitors such asomeprazole (Prilosec, Losec, Omesec, Zegerid), and Pantoprazole (Protonix) are reported to be useful to reduce intracranial pressure.

Antihistamine
Neurologists have been prescribing cimetidine (Tagamet, Zitac), which is a histamine H2-receptor antagonist — an antihistamine.  Histamine contributes to inflammation and  causes  smooth muscles  to constrict.  Cimetidine is diffused into the cerebrospinal fluid and reportedly may contribute to reducing the flow of CSF.  When taken with gabapentin, cimetidine also reportedly may increase the amount of gabapentin in the blood by decreasing its elimination.  Therefore, when taken together, the dosages may require adjustment.

Cimetidine is a potent inhibitor of several families of cytochrome P450 enzymes and can also inhibit transporter pumps and decrease the renal excretion of some drugs, including clearance of many drugs, such as theophylline, lidocaine, midazolam, and propranolol.

Diuretics
Diuretics
furosemide (Lasix, Diuride, Frudix, Frusemide) and spironolactone (Aldactone), also reduce the production of cerebrospinal fluid and are reported to be useful to reduce intracranial pressure. Diuretics are being used infrequently, due to side effects and the success of other CSF pressure reducers.

Carbonic anhydrase inhibitors
Carbonic anhydrase inhibitors,
such as acetazolamide (Diamox) also serve to decrease the flow of cerebrospinal fluid, but their adverse side effects of abdominal pain, lethargy, weakness, and bone marrow suppression limit long term use. Methazolamide (Glauctabs, MZM, Neptazane), also is a carbonic anhydrase inhibitor. Carbonic anhydrase is a protein which can affect fluid production in various parts of the body.  Methazolamide reduces the activity of this protein. It’s initial use was to treat glaucoma by reducing the amount of fluid produced in the eyes and therefore also reducing pressure in the eye.

Other Drugs
Some neurologists are prescribing amantadine (Endantadine, Symmetrel), an N-methyl-d-aspartate antagonist, which is used for control of the symptoms of Parkinson’s disease in humans, together with gabapentin or pregabalin. Amantadine is believed to release brain dopamine from nerve endings making it more available to activate dopaminergic receptors.

Melatonin is a hormone produced by the pineal gland in the brain. Melatonin supplement has been prescribed by veterinarians to ease anxiety and restlessness in dogs. Some vets also have prescribed it for dogs with SM symptoms. Since melatonin is a hormone, it should not be given to dogs without the advice of a veterinarian. Melatonin can have adverse side effects, and in particular, it is contraindicated for dogs that are pregnant or lactating.

Corticosteroids
Before the disease progresses to its severe form, the use of anti-inflammatory corticosteroids, such asprednisolone (Prelone, Prednidale), methyl-prednisolone (Medrol, Medrone), and dexamethasone (Decadron, Dexamethasone Intensol, Dexone, Hexadrol), may relieve the symptoms but not the deterioration.  However, dogs should never be treated with both a cortisteroid and an NSAID at the same time.  Corticosteroids have serious side effects, such as weight, gait, and skin changes, and harmful suppression of the immune system.  Long term use of these drugs is not advised.

Holistic Care
An herbal supplement which cavalier owners report calms dogs suffering from the symptomatic scratching of SM is a product called “Nerve Eight” or “Nerve 8”, manufactured by Nature’s Sunshine of Provo, Utah (left), which consists of white willow bark (salix alba), black cohosh root (cimicifuga racemosa), capsicum fruit (capsicum annuum), valerian root (Valeriana officinalis), ginger root (zingiber officinale), hopsflowers (humulus lupulus), wood betony herb (betonica officinalis), and devil’s claw root (harpago-phytum procumbens).

 

from veterinary-neurologist.co.uk
from veterinary-neurologist.co.uk

Surgery

Surgery to allow the cerebrospinal fluid to flow normally may be necessary to reduce the pain and deterioration.  Surgery is recommended if there is significant pain or a deteriorating condition. The current threshold for surgery seems to consist of dogs with:  (1) MRI evidence of Chiari-like malformation and cervical syringomyelia; (2) Syrinx in the cervical spinal cord measuring ≥3mm diameter on transverse T2 MRI; nd (3) Clinical signs of phantom scratching, cervical pain or hypersensitivity, or thoracic limb paresis without MRI/CSF evidence of other changes that could produce the same clinical signs.

Source: Thank you to cavalierhealth.org for this very helpful information.  Please visit cavalierhealth.org/syringomyelia.htm for complete information, studies, and treatment options.

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