Investigation of Sensory Thresholds in Cavalier King Charles Spaniels with and without Chiari-like Malformations and Syringomyelia

Abstract

Background: Cavalier King Charles Spaniels (CKCS) suffer pain associated with Chiari-like malformation and syringomyelia (CMSM). People suffer from a similar condition and describe numerous sensory abnormalities. Sensory changes have not been quantified in affected CKCS.Objectives: To use quantitative sensory testing (QST) to quantify thermal and mechanical thresholds in CKCS and to compare QST in dogs with and without syringomyelia (SM).Animals: Forty-four CKCS.Methods: Prospective study. Dogs underwent neurological examinations and craniocervical magnetic resonance imaging (MRI). Thermal testing was performed over the humerus and thorax (n = 32); mechanical testing was performed on the paw and neck (n = 44). Latencies, thresholds, and response rates were compared with presence and severity of SM on MRI, presence of pain reported by the owner and pain identified on examination.Results: Thirty dogs had SM, 30 were painful on examination, 29 were owner-reported symptomatic. Thermal and mechanical variables were not significantly different based on presence or severity of SM. Dogs with pain on examination had decreased mechanical thresholds on the paw (0.38 kg, SD = 0.18) and neck (2.05 kg, SD = 0.74) compared to thresholds of dogs without pain on examination on the paw (0.60 kg, SD = 0.30) and neck (2.72 kg, SD = 0.57; P = .021).Conclusions and Clinical Importance: Mechanical and thermal sensitivity does not appear to be related to the presence of SM, but mechanical sensitivity appears to be related to the presence of pain and clinical signs. Mechanical testing may be useful for assessing sensory abnormalities during clinical trials.

Mechanical quantitative sensory testing in cavalier King Charles spaniels with and without syringomyelia

“…The differences in location and prevalence of punctate and static allodynia may explain why our findings differ from another Table 3 Owner-derived clinical sign scores for 10 syringomyelia (SM)-affected CKCS enrolled on or after January 1, 2017. Patient number corresponds to the number listed in Tables 1 and 2 Patient 10 11 12 13 14 15 16 17 18 19 Compulsive scratching 2 4 4 3 3 3 3 2 3 2 Facial rubbing 1 1 3 3 3 3 4 1 2 2 Hypersensitivity to light touch 2 0 4 3 3 2 1 3 2 0 Unexplained yelping 3 0 2 0 2 1 4 0 2 1 Not willing to lift head recent study [9] which did not identify a difference in ST values or thermal latencies in CKCS with and without SM. Sparks et al used hemostatic forceps to apply pressure to the subcutaneous tissues of the neck and thoracic limbs, exclusively evaluating static allodynia [9].…”

“…Patient number corresponds to the number listed in Tables 1 and 2 Patient 10 11 12 13 14 15 16 17 18 19 Compulsive scratching 2 4 4 3 3 3 3 2 3 2 Facial rubbing 1 1 3 3 3 3 4 1 2 2 Hypersensitivity to light touch 2 0 4 3 3 2 1 3 2 0 Unexplained yelping 3 0 2 0 2 1 4 0 2 1 Not willing to lift head recent study [9] which did not identify a difference in ST values or thermal latencies in CKCS with and without SM. Sparks et al used hemostatic forceps to apply pressure to the subcutaneous tissues of the neck and thoracic limbs, exclusively evaluating static allodynia [9]. Static allodynia is less frequently reported in people with neuropathic pain, and when reported tend to affect small areas which may be difficult to map in affected dogs [14].…”

“…An unexpected finding in the present study was the lack of relationship between ST values in SM-affected dogs and syrinx height observed on MRI or difference between SM grades using the BVA scheme. While some studies suggest that syrinx size predicts severity of neuropathic pain-related clinical signs, there is conflicting evidence regarding this relationship in the human and veterinary literature [3,7,9,21,22]. Recently, the focus in human and veterinary medicine has shifted from assessing the size of the syrinx to evaluating the symmetry, with asymmetrical syringes more commonly There is a significant inverse correlation between pelvic limb ST values and clinical signs, suggesting that animals with more pronounced hyperesthesia showed more clinical signs of SM at home (r = −0.657; p = 0.022) associated with neuropathic pain [3,7,23,24].…”

“…An important limitation in our study, and one that begs discussion for all CM/SM studies in CKCS, is the difficulty in identifying a true "normal" population for comparison within the breed. While the importance of CM as a contributor to pain has been historically minimized in dogs with SM, it has been documented in both people and dogs to cause pain in the absence of SM [9,[25][26][27], with or without variable contribution from concurrent craniocervical junction anomalies [28][29][30]. Selection of CKCS without CM or other minor occipital or skull-based malformations proves near impossible due to the ubiquitous nature of these malformations within the breed [7,31].…”

“…Clinical signs of SM include an array of behaviors such as compulsive scratching of the neck and flank, unprovoked vocalizations, and apparent sensitivity to light touch [1,[3][4][5][6][7][8]. While these clinical signs have long been suspected to represent behavioral manifestations of neuropathic pain, studies using quantitative measures of sensation to document a neuropathic pain state in SM-affected dogs are limited [9].…”