Genetic Welfare Problems of Companion Animals

An information resource for prospective pet owners

Cavalier King Charles Spaniel

Cavalier King Charles Spaniel (CKCS)

Syringomyelia

Related terms: syringohydromyelia, hydrosyringomyelia, "neck scratcher's disease", Chiari-like malformation (CM or CLM); Occipital hypoplasia (OH); Caudal occipital malformation syndrome (COMS).

Outline:It was found, in a recent study, that 70% of Cavalier King Charles Spaniels showed syringomyelia by six years of age – the presence of fluid-filled cavities in the spinal cord of the neck. These are caused by abnormal pressures in the fluid that surrounds the spinal cord. The abnormal pressures appear to be associated with malformation of the skull such that the hind part of the brain tends to be pressed back into the foramen magnum – the hole in nthe back of the skull through which the spinal cord runs. This condition is known to be very painful in humans and affected dogs may show signs indicative of head and neck pain. The disease may not become apparent until the dog is older than 2.5 years. Unless it is successfully treated (which is not easy), the condition can cause lifelong pain which can be severe at times.


Summary of Information

(for more information click on the links below)

1. Brief description

Syringomyelia is the formation of fluid filled cavities in the spinal cord because of abnormalities in the pressure of cerebrospinal fluid due to a mismatch between the size of the brain and the skull or with abnormality of the skull shape.

The signs shown by affected dogs are variable. Some show no signs at all, and at the other end of the spectrum, some show severe signs of pain around their head, neck, and forelimbs and may whine, yelp or cry and contort their necks, become withdrawn, develop a weak or wobbling gait, such that walking becomes increasingly difficult. The earliest sign is typically yelping after sudden changes in posture eg when jumping down or being picked up. More severe cases have sensitivity to touch in the neck area and an uncontrollable urge to scratch at ears, chest, neck and shoulders.

2. Intensity of welfare impact

Syringomyelia appears to be quite common in some lines of Cavalier King Charles Spaniels. The welfare consequences vary between individuals but can be serious and very prolonged (months to years). It can cause continuous and severe, disabling pain.

3. Duration of welfare impact

Pain caused by syringomyelia can be very prolonged, that is months or years: throughout life from when it first starts which is typically after 2.5 years of age.

4. Number of animals affected

The proportion of animals affected remains unclear. One survey in the USA indicated that 3.4% of CKCS showed clinical signs (signs of pain). If this reflects the situation worldwide then thousands or tens of thousands of dogs are likely to be affected. The results of a voluntary screening programme in the UK and Netherlands suggested  that the lifetime risk of developing syringomyelia in the study population was 55% (Parker et al 2010).

In a recent survey of 555 Cavalier Kings Charles spaniels reported by their owners to show no clinical signs of the disease, it was found, using MRI scanning, that 25% of one-year olds and 70% of those aged 6 years or more had syringomyelia (Parker et al, 2011).

From data on estimates of total dog population in the UK and on the percentage of all micro-chip registered dogs that are Cavalier King Charles Spaniels (Lucy Asher 2011, personal communication), we estimate that the UK population size of this breed may be around 200,000. 

5.Diagnosis

Magnetic resonance imaging (MRI) is the best method for diagnosis and early detection of syringomyelia.

6. Genetics

The genetics are under investigation. There may be more than one gene involved.  It is estimated that about three-quarters of dogs bred from affected animals are likely to inherit the condition.

7. How do you know if an animal is a carrier or likely to become affected?

There is no genetic test yet and no way to tell, before the onset of signs, whether an animal is going to become affected or not or if it is carrier. Breeding should only be from scanned, negative, animals. Some dogs that are clear when scanned at 12 months will subsequently become affected. For these reasons, it is recommended that breeders scan also at 2-3 years and again at 6 years of age. (www.rupertsfund.com is able to offer free MRI scans for some dogs in the UK)

8. Methods and prospects for elimination of the problem

A computer-based breeding programme pioneered for the Cavalier King Charles is being developed at the Animal Health Trust in the UK. This system is designed to facilitate selection against various genetic diseases while controlling (minimising) inbreeding and further loss of diversity. It depends on accurate measurement of clinical signs of the disease, including those derived from MRI scans (Working Group 2008). The UK’s British Veterinary Association and Kennel Club currently are working towards a programme to standardise MRI scanning methods and to set minimum ages for breeding (Working Group 2008). If animals are carefully selected for breeding based on MRI scan results it is to be hoped that it may be possible to rapidly reduce the prevalence of this disease. However, this is complicated by the need, simultaneously, to select animals for breeding that are free of other genetic diseases to which the breed is prone (notably mitral valve disease). 


For further details about this condition, please click on the following:
(these link to items down this page)


1. Clinical and pathological effects

In affected dogs fluid filled cavities (syringes) form within the spinal cord because of a discrepancy between the size and shape of the skull and brain. This condition, in which the back of the skull is less rounded and smaller than would be considered normal in a similar sized dog, is called a Chiari-like malformation (http://www.ninds.nih.gov/disorders/syringomyelia/detail_syringomyelia.htm).

This malformation leads to an overcrowding and distortion in the shape of the brain (Rusbridge et al 2000), which in turn can lead to a restriction in the flow of cerebrospinal fluid (CSF) between the brain and spinal canal. CSF flow is normally occurs as the brain enlarges slightly with each heartbeat as blood is pumped into resulting in CSF being pumped into the spinal canal (Rusbridge et al, 2006). If the skull is too small, the lower part of the cerebellum and brain stem protrude from their normal locations in the back of the head, to narrow or partly block the hole, the foramen magnum, through which the spinal cord passes and through which cerebrospinal fluid circulates into the spinal canal (Rusbridge et al, 2000). In severe cases the cerebellum may even project into the topmost part of the spinal canal in the neck. To get past this restriction, any cerebrospinal fluid that manages to enter the spinal canal does so because it is forced in at a higher pressure than is normal (Rusbridge et al, 2006). Although the exact mechanism is still not agreed, it seems that this pressure difference between the fluid entering the spine and that already there, in time, causes the spinal cord to swell or pull apart, creating the syrinx, with fluid from surrounding blood vessels being squeezed into the cavity (http://www.ninds.nih.gov/disorders/syringomyelia/detail_syringomyelia.htm; Rusbridge et al 2000; Rusbridge et al 2006).

Syringomyelia Fig1

Figure 1. A CT scan of the brain and spinal cord of a healthy dog showing no signs of syringomyelia. The CSF is able to pass from the brain to the spinal cord freely.

Syringomyelia Fig2 

Figure 2.  A severe case of Syringomyelia. Due to insufficient space for the brain within the skull, part of the brain tissue is protruding out of the skull (red arrow). This is causing the CSF to exit the brain under high pressure, in turn resulting in a fluid filled cavity (white area with asterix), known as a syrinx, within the spinal cord. This damage to the spinal cord leads to the clinical signs outlined below.

The pattern of clinical signs depends upon where the syrinx forms and how far it extends. It is possible however for a dog to have syringomyelia but show no clinical signs, as may occur if the syrinx is narrow (www.cavalierhealth.org). The presence of clinical signs is correlated with the width of the syrinx and extent of spinal cord damage. The region of the cord most commonly damaged is the dorsal horn, the part that receives sensory information and relays it to the brain (http://www.ninds.nih.gov/disorders/syringomyelia/detail_syringomyelia.htm).

Syringomyelia Fig3

Figure 3.  A less severe case of Syringomyelia than that seen in Figure 2. The narrower syrinx may mean there are no clinical signs present.

(Figures 1,2 & 3 are property of the British Veterinary Association and Kennel Club CM/ SM Scheme, to whom we are grateful for permission to reproduce them here).

Pain is by far the most important feature of syringomyelia (Rusbridge 2007). The earliest sign is typically yelping after sudden changes in posture eg when jumping down or being picked up. More severe cases have sensitivity to touch in the neck area and exhibit an apparently uncontrollable urge to scratch at ears, chest, neck and shoulders (Rusbridge 2007). Owners often report that this is worse at night; when first getting up; during hot or cold temperature extremes; or when excited, walking or during other forms of exercise (Rusbridge, 2007; Rusbridge et al 2000). The scratching is typically to one side only but may come to involve both sides.

For these reasons, such scratching differs from that seen in response to skin conditions (in which typically we would expect to see evidence of skin irritation). The scratching is thought to be a result of abnormal skin sensation caused by damage to nerve fibres that convey information about sensations such as touch, pain and temperature from the body to the brain. Humans suffering from the condition have described the resulting skin sensation as varying from a feeling that insects are crawling on the skin, to a severe burning pain (Rusbridge 2007; http://cavaliercampaign.com/cavalier-king-charles-spaniel-health-issues/). Affected dogs may become withdrawn and stop wanting to play. Other clinical signs that may be shown, but which are not unique to the condition, include paw licking and chewing, head shaking, head rubbing, pain on defecation, weakness, poor coordination and scoliosis – curvature of the spine (Rusbridge 2007). Others signs which have been reported but which may be circumstantial are seizures, vestibular (inner ear) disease, deafness and facial nerve paralysis. If the condition progresses and the spinal cord becomes more damaged, dogs show increasingly severe signs of pain around their head, neck, and forelimbs and may frequently vocalise - whine, yelp or cry - and/or become withdrawn and show less inclination to play and run (Rusbridge et al 2000). More severely affected animals may have weakness or a wobbling gait, such that walking becomes increasingly difficult (www.cavalierhealth.org). Some owners of severely affected dogs have also reported that their dogs contort their necks and even sleep and eat only with their heads held high, perhaps to help relieve the pain (http://asap.org/index.php/disorders/canine-syringomyelia/). Some dogs deteriorate to the point of paralysis.

Examples of two of these symptoms, incessant scratching and head rubbing, are displayed in the following videos:

 

 

The rate of progression of the disease is very variable. The clinical course may be acute (rapid onset) or it may progress slowly over several months or years. Dogs may show the first signs at any age but most do before 4 years old. In some cases scratching is infrequent and pain appears only to be mild. In some others, neurological signs may never, or only very slowly, develop. Other cases deteriorate to the point of needing euthanasia.

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2. Intensity of welfare impact

The welfare impact of syringomyelia is due to the mild to severe head and neck pain that it can cause. Pain tends to be most severe in those that have the most severe spinal abnormalities (the largest syrinxes) and which start to show clinical signs of the condition at the youngest age. The pain is likely to be due to the disordered neural processing caused by the syrinx pressing on and damaging the spinal cord (Rusbridge et al 2006). The pain is hard to relieve using conventional pain relieving medication. (Rusbridge et al 2007; Rusbridge and Jeffrey 2008).

Both the degree to which syringomyelia affects an animal, and the progress of the condition, can be extremely variable. Some dogs that have the condition may, if the syrinx is small and narrow, show no scratching or other signs of pain. In such cases, although there is no welfare impact on that dog, if it is used for breeding, there is a risk of offspring being clinically affected (Rusbridge and Knowler 2004).

As syrinx diameter increases, more severe signs are exhibited, with increased scratching, scoliosis (curvature) of the spine and signs of pain (Rusbridge et al 2007). Such severely affected dogs are very sensitive to being touched around their head, neck, and forelimbs and will show pain if handled in these areas. They may also yelp or scream for apparently no reason and become increasingly disabled by pain (Rusbridge et al 2004).

Affected dogs often seem to try to minimise the pain by positioning their head so as to ease cerebrospinal fluid flow and reduce any blockage and the pain it causes (http://asap.org/index.php/disorders/canine-syringomyelia/). Such dogs may even sleep and eat only with their heads held high, although long-term adoption of this posture is also likely to be painful. There may also be progressive weakness and poor coordination so that walking becomes increasingly difficult (Rusbridge 2007).

Although many dogs with this condition can lead relatively normal lives if they are carefully managed (but we should be cautious to assume that there is no impact on the quality of their lives), some dogs progressively deteriorate and are euthanised on welfare grounds (Rusbridge and Knowler 2003; Rusbridge et al 2000; http://cavaliercampaign.com/cavalier-king-charles-spaniel-health-issues/).

The most severely affected dogs suffer severe, continual constant pain; whimpering and crying with no obvious triggers and will exhibit great reluctance to move (Rusbridge et al 2000). Such severe clinical signs can develop within twelve months of the first signs of the condition (www.cavalierhealth.org).

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3. Duration of welfare impact

Affected dogs may experience pain throughout their life after the problem develops – and for Cavaliers the first signs of pain are typically seen when they are 2.5 years or older, although syringomyelia can develop earlier than this (Rusbridge 2007). Approximately 45% of affected dogs develop the first behavioural signs of the condition within the first year of life and 40% between 1 and 4 years old (Rusbridge 2007).

The most mildly affected dogs, as diagnosed by detection of syrinx on an MRI scan, show no obvious clinical signs and can lead relatively normal lives. They may suffer little or no pain, and any pain occurring may be only for brief episodes (seconds).

Mildly affected dogs may exhibit short-lived discomfort. Such discomfort seems to occur or be made worse through activities that cause cerebrospinal fluid pressure to fluctuate suddenly and is therefore often apparent during or after excitement or activity (Rusbridge 2007; Rusbridge et al 2000). This discomfort may last for some minutes.

More severely affected animals are likely to experience daily, constant low to high level pain, evidenced by a tendency to hold their heads up, and to eat and sleep in this position; presumably to reduce the pain (Rusbridge et al 2000).

The most severely affected dogs suffer severe, continual constant pain; whimpering and crying with no obvious triggers and will exhibit great reluctance to move (Rusbridge et al 2000). Such severe clinical signs can develop within twelve months of the first signs of the condition (www.cavalierhealth.org).

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4. Number of animals affected

Syringomyelia is a widespread condition in Cavaliers and has been reported in many countries and from various breeding lines.

Estimates of the proportion of UK Cavaliers showing Chiari-like malformation, range from 50% to 95-100% (Rusbridge and Knowler 2003; Rusbridge et al 2005; Kibar et al 2008) it is expected that this is similar in other countries. Not all of these dogs show clinical signs of syringomyelia, but MRI studies in the UK and elsewhere have found that of those dogs scanned aged two and a half or older, 37 - 74% exhibit neurological changes indicative of syringomyelia (Kibar et al 2008; CAWC, 2008; Couturier et al 2008). The results of a voluntary screening programme in the UK and Netherlands suggested  that the lifetime risk of developing syringomyelia in the study population was 55% (Parker et al 2010). In a recent survey of 555 Cavalier Kings Charles spaniels reported by their owners to show no clinical signs of the disease, it was found, using MRI scanning, that 25% of one-year olds and 70% of those aged 6 years or more had syringomyelia (Parker et al, 2011).

Surveys of the proportion of Cavalier King Charles Spaniels showing clinical signs report results ranging from 0 to 35% (Rusbridge et al 2005; CAWC, 2008). A questionnaire-based survey analysed at Purdue University, USA, indicated 3.4% incidence of clinical syringomyelia in the Cavalier population. If this figure is representative of the prevalence around the world then this would suggest that, worldwide, thousands of these dogs are suffering with pain as a result of this condition. It is estimated that there are more than 11,000 Cavalier King Charles Spaniels registered each year in the UK alone (and a similar number born that are not registered) (CAWC 2008). From data on estimates of total dog population in the UK and on the percentage of all micro-chip registered dogs that are Cavalier King Charles Spaniels (Lucy Asher 2011, personal communication), we estimate that the UK population size of this breed may be around 200,000.  The results of a voluntary screening programme in the UK and Netherlands suggested that the lifetime risk of developing syringomyelia in the study population was 55% (Parker et al 2010)

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5. Diagnosis

Magnetic resonance imaging (MRI) is the best method for diagnosis of syringomyelia (Rusbridge et al 2006), as it can provide detailed images of body structures including brain and spinal cord. This method reveals fluid-filled cavities within the spinal cord of affected animals. In severe cases, the syrinx can be so wide that only a thin rim of the spinal cord is visible. In humans, MRI scanning is a painless and informative procedure and it has greatly improved the diagnosis of syringomyelia (http://www.ninds.nih.gov/disorders/syringomyelia/detail_syringomyelia.htm). Use of the method in dogs does, however, require that the animals are anesthetized and it is expensive.

Many breeders of Cavalier King Charles spaniels choose to screen their breeding stock using MRI to detect subclinically affected animals (those which have syrinxes but which show no clinical signs). The minimum age for screening is 12 months. However syringomyelia is a late onset condition and some dogs that are clear at 12 months will subsequently become affected. For these reasons, it is recommended that breeders also determine the MRI status of their breeding stock at 2-3 years and again when 6 years of age.

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6. Genetics 

An on-going study of the genealogy of 10,600 related Cavaliers across three continents has suggested that Chiari-like malformation and syringomyelia are hereditary conditions and that affected individuals share a common ancestry back to two of the six dogs from which the modern breed originated (Rusbridge 2007). The breed was established in 1928 (Rusbridge and Knowler,2003).

Breeding from dogs with this ancestry, especially inbreeding between dogs showing the condition, has been linked to an earlier onset of the condition and a tendency for the condition to be more severe (Rusbridge and Knowler 2003, 2004; Rusbridge et al 2005). Early estimates of the heritability of syringomyelia suggest values of around 0.7-0.8, that is, that 70-80% of the variation between individuals is genetic in origin and about 20-30% is environmental (Working Group 2008), and that approximately three-quarters of dogs bred from affected animals are likely to inherit the condition (Blott 2008). This estimate of heritability is sufficiently high to suggest that genetic selection against the disease could be very successful. In addition heritabilities for Chiari-like malformation are also very high. Although there is a positive correlation between these Chiari malformation and syringomyelia, there is not a one to one correlation which suggests that different genes may be controlling the expression of syringomyelia and Chiari-like malformation and that it may be possible to select against syringomyelia even if dogs have Chiari-like malformation.

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7. How do you know if an animal is a carrier or likely to become affected?

There is no way of knowing, before signs of syringomyelia are shown, whether an animal will be affected, unaffected, or unaffected but a carrier of the gene (carriers do not develop the disease themselves but can pass it on to their young). The earliest age at which the signs are shown is 6 months of age, but for many affected dogs the condition may not be apparent even years later. An MRI scan is the only certain way of detecting the presence or absence of the syrinx and other neurological changes associated with syringomyelia and for this reason, to avoid breeding from affected dogs and so increasing the number of dogs that will suffer from this condition, it is strongly advised that any Cavalier to be used for breeding should be scanned for the presence of the condition (Rusbridge 2007; CAWC 2008).

This need for a clean bill of health before breeding is particularly important because examination of the pedigrees of the 25 top stud dogs for the last 5 years showed that, not only were many very closely related, but they all were descendants of suspected carriers of syringomyelia. Some dogs that are clear when scanned at 12 months will subsequently become affected. For these reasons, it is recommended that breeders also determine the MRI status of their breeding stock at 2-3 years and again when 6 years of age. (www.rupertsfund.com is able to offer free MRI scans for some dogs in the UK)

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8. Methods and prospects for elimination of the problem

A computer-based breeding programme pioneered for the Cavalier King Charles is being developed at the Animal Health Trust in the UK. This system is designed to facilitate selection against various genetic diseases while controlling (minimising) inbreeding and further loss of diversity. It depends on accurate measurement of clinical signs of the disease, including those derived from MRI scans (Working Group 2008). The UK’s British Veterinary Association and Kennel Club currently are working towards a programme to standardise MRI scanning methods and to set minimum ages for breeding (Working Group 2008). If animals are carefully selected for breeding based on MRI scan results it is to be hoped that it may be possible to rapidly reduce the prevalence of this disease. However, this is complicated by the need, simultaneously, to select animals for breeding that are free of other genetic diseases to which the breed is prone (notably mitral valve disease). 

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9. Acknowledgements

UFAW is grateful to Rosie Godfrey BvetMed MRCVS and David Godfrey BVetMed FRCVS for their work in compiling this section and to Stephanie Kaufman for assistance in illustrating it.

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10. References

Blott S (2008) Genetics of syringomyelia and breeding strategies to reduce occurrence. Notes for the Cavalier King Charles Spaniel Clubs Liaison Meeting 18 May 2008, Animal Health Trust, UK

Couturier J, Rault D and Cauzinille L (2008) Chiari-like malformation and syringomyelia in normal cavalier King Charles spaniels: a multiple diagnostic imaging approach. J. Small Animal Practice 49: 438-443

Parker JE,  Knowler SP, Rusbridge C, McKinley TJ, Noorman E and Jeffery ND (2010) The Incidence of Syringomyelia in the Cavalier King Charles Spaniel. Abstract at 23d European College of Veterinary Neurology Symposium, September 2010

Parker JE, Knowler SP, Rusbridge C, Noorman E & Jeffery ND (2011)  Prevalence of asymptomatic syringomyelia in Cavalier King Charles spaniels. Veterinary Record 168 :667.  doi : 10.1136/vr.d1726

Rusbridge C (2007) Chiari-like malformation and Syringomyelia in the Cavalier King Charles Spaniel, PhD dissertation, University of Utrecht

http://igitur-archive.library.uu.nl/dissertations/2007-0320-201201/full.pdf

http://www.ninds.nih.gov/disorders/syringomyelia/detail_syringomyelia.htm

Rusbridge C and Knowler SP (2003) Hereditary aspects of occipital bone hypoplasia and syringomyelia (Chiari type I malformation) in Cavalier King Charles Spaniels. Veterinary Record 153: 107-112

Rusbridge C, Macsweeny JE, Davies, JV, Chandler K, Fitzmaurice SF, Dennis R, Cappello R and Wheeler SJ (2000) Syringohydromyelia in Cavalier King Charles Spaniels. J American Animal Hospital Associate 36: 34-41

Rusbridge C, Greitz D and Iskandar BJ (2006) Syringomyelia: Current concepts in pathogenesis, diagnosis, and treatment. J Vet Intern Med 20(3)::469–479

www.cavalierhealth.org

http://cavaliercampaign.com/cavalier-king-charles-spaniel-health-issues/.

http://asap.org/index.php/disorders/canine-syringomyelia/

Rusbridge C and Knowler SP (2004) Inheritance of occipital bone hypoplasia (Chiari type I malformation) in Cavalier King Charles Spaniels. Journal of Veterinary Internal Medicine 18: 673-678

Rusbridge C, Carruthers H, Dubé MP, Holmes M and Jeffery ND (2007) Syringomyelia in cavalier King Charles Spaniels: the relationship between syrinx dimensions and pain. J Small Anim Pract. 48::432-36

Rusbridge C and Jeffrey ND (2008) Pathophysiology and treatment of neuropathic pain associated with syringomyelia. Vet. J 175: 164-172

Rusbridge C, Knowler P, Rouleau GA, Minassian BA and Rothuizen J (2005) Inherited occipital hypoplasia/syringomyelia in the Cavalier King Charles Spaniel: Experiences in setting up a worldwide DNA collection. Journal of Heredity 96: 745-49

Kibar Z, Rouleau G, Dubé MP, Rubsbridge C, Knowler P and Blott S  Identification of genes causing Chiari- like Malformation with Syringomyelia in the Cavalier King Charles Spaniel. http://www.cavaliersonline.com/health/syringoinfo.htm.

Fixing ancestral problems: Genetics and welfare in companion animals focusing on syringomyelia in Cavalier King Charles Spaniels as an example. Report of the Companion Animal Welfare Council Workshop Tuesday 29th April 2008, House of Lords.

Working Group (2008) Report of the Meeting to discuss proposed BVA KC Syringomyelia MRI screening scheme held on 24th October at the British Veterinary Association, 7 Mansfield Street, London, W1G 9NQ (link to document here)

© UFAW 2012


Credit for main photo above:

By Philippe Brizard (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons