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M. Thøfner1
1Faculty of Health and Medical Sciences, Department of Veterinary Clinical Sciences, Frederiksberg, Denmark
Maria Søndergaard Thøfner, DVM, Phd student
Department of Veterinary Clinical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen.
Dyrlægevej 16, DK-1870 Frederiksberg C, Denmark. E-mail:
Syringomyelia and Chiari-like malformation is a hereditary and incurable neurological disease complex in the Cavalier King Charles Spaniel (CKCS). The suggested mode of inheritance is polygenic with variable penetrance. Chiari-like malformation (CM) is a developmental skull anomaly characterised by occipital bone hypoplasia and secondary reduced volume of the caudal cranial fossa. This results in caudal cranial fossa overcrowding characterised by a volume mismatch between the reduced intracranial volume and increased cerebellar volume, which leads to cerebellar indentation and partial herniation into the foramen magnum. The consequence of the overcrowding and cerebellar herniation is a subarachnoidal stenosis that alters the pressure and  ow dynamics of the cerebrospinal  uid.
Syringomyelia (SM) is de ned as a  uid- lled cavity (syrinx) in the spinal cord parenchyma. The CM/SM complex was originally described in 2000 by Rusbridge et al. (1). The causal relationship between CM and the development of SM is still controversial. It has been suggested that the syrinx formation is a result of pressure differences between the spinal cord parenchyma and
the subarachnoidal space. The cerebrospinal  uid transport is pulsatile and synchronous with the cardiac rhythm. The CM/SM patient has an increased systolic cerebrospinal  uid pressure due to cerebellar prolapse and secondary subarachnoidal stenosis. The result is a sucking effect that facilitates transport of cerebrospinal  uid from the subarachnoidal space into the spinal
cord parenchyma. This vicious circle induces the syrinx formation. The cross-sectional increase in the syrinx area enlarges the overall cross-section of the spinal cord. As a consequence, the subarachnoidal space is reduced and the systolic pulsatile pressure of cerebrospinal
 uid increases accordingly (2). SM is also seen in other breeds, often secondary to trauma, in ammation
or intervertebral disc degeneration but never with concurrent CM.
The prevalence estimation of SM in CKCS is challenging since the de nitive diagnosis requires magnetic resonance imaging (MRI) con rmation. In addition, it is important to stress that CKCS with MRI con rmed SM can be asymptomatic. A retrospective British/Dutch study on asymptomatic CKCS has shown an age- dependent increase in the prevalence of asymptomatic SM from 25 % to 70 % in CKCS between 12 and 72 months of age (3). In Danish CKCS the prevalence of symptomatic SM is 15 % (4).
The clinical manifestation of SM includes characteristic behavioural changes; these are presumably associated with central neuropathic pain. Central neuropathic pain
is de ned as ‘pain caused by a lesion in the central somatosensory nervous system’ by the International Association for the Study of Pain and is characterised
by allodynia (pain as a result of non-noxious stimuli)
and hyperalgesia (increased pain sensation as a result
of noxious stimuli). Some cases also present with neurological symptoms (eg. proprioceptive or lower motor neuron de cits). The most prevalent clinical signs are: intermittent spontaneous or evoked scratching;, reluctance to be touched in the head and neck region; and in severe cases, paroxysmal pain manifestations with vocalisation, intense scratching, rubbing and circling on the ground oor. The scratching is uni- or bilateral and
is directed at the head, ears, neck, shoulders, axillae, chest or ventral abdomen. Phantom scratching, a re ex without skin contact, can also be seen and is indicative of dysaesthesia (an unpleasantly abnormal sensation). Factors that aggravate the scratching are collars and harnesses, excitement and stressful situations. Some dogs are reluctant to wear collars or harnesses. Others resist being groomed or touched on the neck, ears and other extremities. In most cases one also  nds a history of sleeping dif culties, restlessness, hypersensitivity
to noise, sunlight and wind and reduced contact
with the owner, other dogs and other people (5). In humans, the SM-associated damage to nociceptive
and other sensory pathways of the spinal cord causes pain and is a prominent feature in 50 – 90 % of adult patients. The pain phenomena are classi ed as central, neuropathic pain, and the patients report neck and back pain or dysaesthesia characterised by burning pain, hyperaesthesia and pins and needles (6).
An Urban Experience

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