Further validation of a pruritus severity scale for use in dogs

Abstract

A scale to assess the severity of pruritus in dogs was further validated. Comparison of the scale with one containing visible numerical markings demonstrated that owners were heavily influenced by the presence of numbers, resulting in a loss of the scale's ability to generate continuous data. The presence of a traditional visual analogue scale was therefore essential. The scale was tested on 713 owners who presented their dogs for veterinary attention. Pruritus scores in 408 dogs with skin disease covered the full range of possible values (0 to 10). In 305 dogs with no skin disease, 90 owners gave a score greater than zero. Comparison of the scores seen in pruritic dogs, and dogs with no evidence of skin disease, allowed a 'normal range' of 0-1.9 to be established. The scale was able to discriminate between conditions typically regarded as pruritic or non-pruritic. When the scale was assessed for its ability to detect changes in pruritus score following treatment, a median reduction of 4.4 points was observed. The scale was also used to determine what magnitude of response owners would expect following treatment of their pruritic dogs. Only 12% would have been satisfied with a 50% reduction, a figure that is typically quoted as a satisfactory response in clinical trials of anti-pruritic drugs. As a result, alternative methods of assessing clinical trials are proposed. This study has shown the scale to be a valuable tool for clinical assessment of patients, and for monitoring treatment responses in clinical trials.