Neuro-sensitization in cats with chronic pain and its association to osteoarthritis progression.

Feline osteoarthritis (OA) is characterized by somatosensory neuro-sensitization, assessed through quantitative sensory testing. It was hypothesized that somatosensory neuro-sensitization would increase with OA pain severity, as categorized through the validated Montreal Instrument for Cat Arthritis Testing, for Veterinarians (MI-CAT(V)). Healthy (n = 10) and cats with naturally occurring OA (n = 121) were enrolled in this prospective, negatively controlled study. Peripheral and spinal sensitization were respectively assessed by paw withdrawal threshold (PWT) and response to mechanical temporal summation (RMTS). PWT determined allodynia threshold. Derived from MI-CAT(V), cats were sorted into four validated OA severity clusters, from absent to severe OA pain. Outcomes were compared across allodynia status (healthy, non-allodynic and allodynic) and OA clusters, while testing for the influence of demographic data, with alpha set at 5%. The PWT, RMTS, MI-CAT(V) outcomes and age accurately discerned between healthy and OA animals (P < 0.002), but not body weight. Non-allodynic cats had similarly altered MI-CAT(V) and RMTS to allodynic cats, but they were younger (P = 0.010) and had a higher PWT than allodynic (P < 0.001), and similar PWT (P = 0.925) but older (P < 0.001) than healthy cats. Spinal sensitization was similar in the three OA-affected clusters (mild-moderate-severe; P = 1.000), but MI-CAT(V) categorized them sensitively (P < 0.001). The mild cluster included more non-allodynic cats than the moderate (P = 0.021) and severe (P = 0.026) clusters. Interestingly, 32% of mild OA cats were allodynic, when the proportion increased to 61% in pooled moderate/severe OA cats (P = 0.013). OA cats are sensitized compared to healthy cats, and peripheral sensitization seems to increase with OA severity (or vice-versa?), which influences pain phenotype.