Syringomyelia Awareness: Syringomyelia Made Simple Part 1

Copyright © Clare Rusbridge BVMS PhD DECVN MRCVS

CANINE CHIARI-LIKE MALFORMATION AND SYRINGOMYELIA

Syringomyelia (SM) is characterised by fluid filled cavities within the spinal cord. SM occurs secondary to obstruction of cerebrospinal fluid (CSF) especially if that obstruction is at the foremen magnum. The most common predisposing cause in the dog is Chiari-like malformation (CM) (Rusbridge and others 2006). The primary clinical sign of CM/SM is pain, either due to obstruction of the CSF pulse pressure and/or a neuropathic pain syndrome due to damage to the spinal cord dorsal horn.

Chiari-like malformation (CM) is a condition characterised by disparity in size between the brain (too big) and the caudal fossa (too small) such that the cerebellum and brain stem are herniated into or through the foramen magnum (Cross et al 2009).

PATHOGENESIS

The pathogenesis of canine CM/SM is not fully understood. An important contributory factor is thought to be the mismatch in size between the brain and skull volume. Studies in the Griffon Bruxellois (Rusbridge et al 2009) have suggested that CM is characterised by a shortening of the basicranium and supraoccipital bone with a compensatory lengthening of the cranial vault especially the parietal bone. This has led to the hypothesis that the condition may be due to insufficiency of the bone and /or craniosynostosis of the lambdoid (occipitoparietal) and cranial base sutures.
The precise pathogenetic mechanism of development of syringomyelia is much debated (reviewed by Rusbridge et al, 2006; Greiz, 2006). A popular theory is that obstruction of CSF flow results in relative increase in spinal cord pressure and decrease in pressure in the CSF space around the spinal cord, the consequence of which is repeated mechanical distention of the spinal cord. This in turn results in dilatation of the central canal and accumulation of tissue fluid which eventually coalesces into cavities.

One of the enigmas of CM/SM is the difficulty of predicting / explaining which dogs with CM will subsequently develop SM. CM is almost ubiquitous in Cavalier King Charles spaniels (CKCS); Cerda-Gonzalez et al (2009) found that 92% had at least one craniocervical morphologic abnormality detected in MR images. However severity of the CM does not predict the presence of SM (Caruthers et al 2006 Cerda-Gonzalez et al, 2009) although CKCS with clinical signs related to syringomyelia are more likely to have a smaller ratio of cauda fossa (i.e. back of skull) volume to total brain volume compared to unaffected CKCS (Cerda-Gonzalez et al 2009). This suggests that there are other unidentified anatomical or environmental factors influencing the development of SM. Both CM and SM have been shown to be inherited in the CKCS (Lewis 2009; personal communication).

INCIDENCE
The CKCS is overwhelmingly overrepresented for cases of CM/SM. There is no colour or sex predisposition. As shortened skull is a risk factor, any breed with a degree of brachycephalism and/or miniaturization could potentially be predisposed to CM/SM. To date the condition has been also reported in King Charles Spaniels, Griffon Bruxellois, Yorkshire Terriers, Maltese Terriers, Chihuahuas, Miniature Dachshunds, Miniature/Toy Poodles, Bichon Frisé, Pugs, Shih Tzus, Pomeranians, Staffordshire bull Terriers, Boston Terriers, French Bulldogs a Pekingese, a miniature Pinscher and a couple of cats.

Not all dogs with SM have clinical signs. The presence of signs is correlated to the width of the syrinx and extent of spinal cord dorsal horn damage. Syrinxes can progressively expand and a dog which is asymptomatic in early life may eventually become painful.

The clinical course may be acute or run an extended course over several months or years. The youngest reported dogs with SM have been 12 weeks old. Dogs may be presented at any age although the majority of dogs (approximately 45%) will develop first signs of the disease within the first year of life and approximately 40% of cases have first signs between 1 and 4 years old. As many as 15% develop signs as mature dogs with the oldest reported case first developing signs of disease aged 6.8 years. Due to the vague nature of signs in some cases and lack of awareness about the disease there is often a considerable time period (mean 1.6 years) between the onset of signs and confirmation of a diagnosis.

CLINICAL SIGNS

The most important and consistent clinical sign of CM/SM is pain however this may be difficult to localise. Owners may describe postural pain; for example, affected dogs may suddenly scream and/or lie with the head on the ground between the paws after jumping up or during excitement. It is also common to sleep with the head in unusual positions, for example elevated. Discomfort often appears worse in the evening and early morning or when excited and can be associated with defaecation or may vary with weather conditions. Pain is positively correlated with syrinx width and symmetry i.e. dogs with a wider asymmetrical syrinx are more likely to experience discomfort, and dogs with a narrow syrinx may be asymptomatic, especially if the syrinx is symmetrical. Dogs with a wide syrinx may also scratch, typically on one side only, while the dog is walking and often without making skin contact, such behaviour is often referred to as an “air guitar” or “phantom” scratching. Dogs with a wide syrinx are also more likely to have scoliosis. In many cases the scoliosis slowly resolves despite persistence of the syrinx.

SM may result in other neurological deficits such as thoracic limb weakness and muscle atrophy (due to ventral horn cell damage) and pelvic limb ataxia and weakness (due to white matter damage or involvement of the lumbar spinal cord by the syrinx). Seizures, facial nerve paralysis and deafness may also be seen; however, no direct relationship has been proven and this association may be circumstantial.

CM alone appears to cause facial pain in some dogs with owners describing ear and facial rubbing/scratching. It has been proposed that CM and compression of the brain stem can result a pain syndrome (Thimineur et al, 2002). In this circumstance it can be difficult to be certain that the CM, as apposed to ear, oral or skin disease, is the cause of the distress especially as CM is a common incidental finding in the CKCS breed.

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Comments

  1. I dont want someone to take this the wrong way but I think I heard about this disease a few years ago and it was from inbreeding the cavalier king charles spaniels is this correct that its genetic? Or was that something else? It was about the brain growing larger than the skull and the dogs having sezuires?

  2. Grace Matthews says:

    Wow I had never heard of this before…how terrible.

  3. WOW! Thank you so much for this article (and all the others ones that I'm about to read). I had never heard of chiari until I was pregnant with my last child. I'm not the type to get the typical headache and when I do, I rarely take anything for it. Out of the blue, I started getting these strange headaches at the base of my skull in the back, right by my neck. The best way to describe the pain is like a contraction when you are in full labor. There wasn't any warning and they didn't just gradually get worse. When they came, they came hard and full force and could stop just as easy as they came. I noticed they seemed to come when I was laughing a lot, coughing a lot (when you have a chest cold), or when I bent over. They started coming more regular and then I started hearing a sound similiar to the sound of a cassette tape playing while the rewind button was also being pushed. It scared me enough to finally go to the doctor and say this is just not normal and something is definitely wrong. Long story short, after some test, I found out I had arnold chiari syndrome. With all that being said and done, I absolutely can not imagine a dog, cat, etc. having to deal with that kind of pain. And especially when they can't talk to tell someone and most people haven't even heard of this (human form or animal form). Now, it has me thinking back to any of my pets wondering if any of them might of had this. And I'm also going to be looking at all pets wondering now. I am very happy that you are spreading the word about this because I can tell you that a lot of people are not aware of this.

  4. Wow, I thought that it was a condition only found in Cavaliers, I had no idea that it was in other breeds or even in people.

    I don't think a lot of people realize just how many conditions that humans can have that pets can have as well.

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