Development and psychometric validation of pain scales in feline osteoarthritis

Radiographic signs of osteoarthritis are prevalent in cats, becoming more common with age. Historically, the rate of diagnosis has tended to be low, suggesting that signs are subtle and/or tend to be attributed to normal age-related changes or to other geriatric diseases. However, cats with osteoarthritis display signs that are responsive to analgesic treatment. This project aimed to develop and validate rating scales for detection and measurement of feline osteoarthritis pain and related disability (the Montreal Instruments for Cat Arthritis Testing). Two such scales, one for use by caretakers/owners [MI-CAT(C)], and one for use by veterinarians [MI-CAT(V)], were developed based on a review of the literature, expert opinion, and a survey study of owners of cats with a diagnosis of osteoarthritis. The content validity (via expert review) was excellent for both scales. A pilot study in a colony of laboratory cats with naturally-occurring osteoarthritis evaluated reliability and ability to detect osteoarthritis status, for both scales; preliminary revisions were made based on the results. The MI-CAT(C) owner scale subsequently underwent validation in a clinical trial of meloxicam in client-owned osteoarthritic cats. Evidence for validity included the ability to distinguish placebo from active treatment, and correlations with objectively measured activity and age. Owners found most scale items clear/easy to understand, preliminarily supporting comprehensibility and face validity (acceptability). Evaluation of intra- and inter-rater reliability suggested that secondary owners varied substantially in their ability to complete the scale, compared to primary owners. A preliminary assessment of internal consistency reliability supported homogeneity, without redundancy, of the scale. The MI-CAT(V) veterinary scale was evaluated in a study of laboratory cats with and without naturally-occurring osteoarthritis. Intra- and inter-rater reliability assessments suggested that a naïve user’s ability to use the scale was influenced by experience with it. The scale was unable to distinguish osteoarthritic and non-osteoarthritic cats, but the subcategories Gait and Posture were somewhat promising based on a non-significant tendency to detect osteoarthritis status, and correlations with an objective measure of osteoarthritis pain, peak vertical force. Palpation of the limbs did not detect osteoarthritis status. A video analysis was performed to increase MI-CAT(V) scale sensitivity to osteoarthritis. Subsequent evaluation and refinements based on three therapeutic trials (involving gabapentin, tramadol, and oral transmucosal meloxicam treatments) in laboratory cats with and without naturally-occurring osteoarthritis resulted in good to excellent intra- and inter-rater reliability, and ability to detect osteoarthritis status. Preliminary evidence supported scale internal consistency. Therapeutic response detected by objective outcome measures was not demonstrable using the scale. It is recommended that the MI-CAT(C) owner scale be evaluated for ability to distinguish osteoarthritic from non-osteoarthritic cats. The MI-CAT(V) veterinary scale requires testing in client-owned cats, and potentially further refinements to permit detection of treatment effects, if it is to be used as more than a disease screening tool. Both scales require additional investigation of internal structure and comprehensibility, and determination of cut-points to guide clinical use (e.g., minimally important difference, and thresholds for classification of cats as osteoarthritic vs. non-osteoarthritic), and evaluation of their feasibility and clinical utility.

Keyphrases: psychometric, metrology, pain scale, cat, behavior, geriatric, degenerative joint disease, chronic pain, quality of life