Assessment of chronic pain in companion animals : development and concurrent validation of neurophysiological methods
Pain is a complex experience involving sensory and perceptual components. It causes stress, suffering and decreased quality of life. Chronic painful conditions such as osteoarthritis (OA) and bone cancer affect cats and dogs. Pain in these conditions results from numerous mechanisms affecting the peripheral and central nervous systems which generate and maintain pathological pain in affected individuals. Quantitative sensory testing (QST) are means to quantify the sensory component of pain. In combination with observed analgesic efficacy, they can be used to study mechanisms of pain. Initial work on cats and dogs with OA has helped to develop and validate some QST methods; however, questions remained unanswered in cats with OA, and this methodology was not yet explored in dogs with bone cancer. Our main hypotheses were: 1) osteoarthritic cats are affected by neurophysiological changes characteristic of central sensitization which can be detected by QST and the concomitant administration of centrally-acting analgesics; and 2) bone cancer in dogs causes peripheral and central sensitization with deficient descending modulating mechanisms. Our main objectives were: 1) to provide evidence of mechanism-based therapy in cats with OA using QST; and 2) to test the ability of a QST protocol to provide evidence of peripheral and central sensitization in dogs with bone cancer including the development and validation of a conditioned pain modulation test, and to test the efficacy of a step-wise palliative analgesic protocol in these patients. Using static and dynamic QST in osteoarthritic cats, we demonstrated that centrally-acting analgesics such as tramadol can reverse central sensitization as measured by facilitated temporal summation of pain, while the same is not observed when a peripherally-acting analgesic such as non-steroidal anti-inflammatory drug, meloxicam, is administered. These findings highlight the importance of mechanism-based approach for the treatment of chronic pain. The QST protocol developed for use in dogs revealed that dogs with bone cancer are affected by primary and secondary hyperalgesia and brush allodynia when compared 5 with healthy dogs. A conditioned pain modulation test which can be easily applied into clinical practice was developed and demonstrated ability to differentiate between healthy and cancerous dogs. Using this methodology, the latter population was found to be affected by deficient descending modulating systems. These studies provided evidence of the similarities in sensory profile between people and companion animals affected by OA- and bone cancer-related pain. The use of QST is valuable in veterinary pain research and should be accompanied by the highest standards of animal care and study design, conduct and reporting.
Cats Bone cancer Central sensitization Chronic pain Dogs Quality of life Quantitative sensory testing Osteoarthritis Peripheral sensitization