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.

Keywords: neuropathic pain; paresthesia; phantom scratch; syrinx.

Figure 1

Quantitative sensory testing instruments and locations; (A) handheld Physitemp thermal probe used for heat and cold testing; (B) hemostratic forceps with a digital load cell used for mechanical testing. Thumb pressure was applied over the central button of the load cell; (C) testing locations for thermal (black squares) and mechanical testing (black stars)

Figure 2

Box‐plots showing thermal latencies (A) and mechanical thresholds (B) in dogs with and without syringomyelia. For thermal testing, every location is displayed as an average of left and right sides and triplicate trials per dog. For mechanical testing, left and right sides were averaged and every dog was tested once per location. The bottom and top of the boxes are the first and third quartiles, the line inside the box is the second quartile (median), the ends of the whiskers represent the lowest data within 1.5 x IQR of the lower quartile and the highest data within 1.5 x IQR of upper quartile. Dots represent outliers

Figure 3

Box‐plot showing thermal latencies (A) and mechanical thresholds (B) in dogs differentiated by pain on neurological examination. For thermal testing, every location is displayed as an average of left and right sides and triplicate trials per dog. For mechanical testing, left and right sides were averaged and every dog was tested once per location. Refer to Figure 2 legend for a description of the box‐plot construct. * Indicates P < .05

Figure 4

Box‐plot showing thermal latencies (A) and mechanical thresholds (B) in dogs that were owner‐reported symptomatic or asymptomatic. For thermal testing, every location is displayed as an average of left and right sides and triplicate trials per dog. For mechanical testing, left and right sides were averaged and every dog was tested once per location. Refer to Figure 2 legend for a description of the box‐plot construct