Osteoarthritis and pain phenotype in dogs

Defining a pain phenotype that is predictive of altered central pain processing in dogs with spontaneous osteoarthritis

In man it is recognised that distinct types of pain, with different underlying causes, exist. However, clinical pain in animals is still considered to be a single entity, regardless of the cause. Knowledge of different patterns of clinical pain (i.e. pain phenotypes) in animals and subsequently the relationship between pain phenotype and underlying aetiopathogenesis of pain is required to advance our understanding of pain mechanisms in animals with spontaneous disease, and to allow a mechanism-based approach to analgesic treatment. The aim of the current proposal is to investigate the relationship between pain phenotype and pain mechanisms using hip and stifle osteoarthritis (OA) in dogs as a spontaneous pain model. The underlying aetiopathogenesis of pain in individual dogs suffering from OA will be established by determining whether there is only altered peripheral (i.e. joint) processing of pain or whether there is altered peripheral AND central (brain and spinal cord) pain processing, by measuring hindlimb nociceptive withdrawal reflexes, temporal summation and assessment of diffuse noxious inhibitory control in dogs with OA and a cohort of healthy CONTROL animals. Subsequently we will define pain phenotypes in our study population by assessing sensitivity to multiple sensory modalities to characterise altered pain sensitivity in dogs with OA relative to CONTROL animals. We will then explore and categorise pain phenotypes that are associated with altered central and/or peripheral pain processing. This proposal represents the first step in understanding the relationship between neurobiological mechanisms and pain phenotype in non-human species and will significantly improve the lifelong welfare of many dogs by: 1) Allowing rational selection of analgesic drugs that target the underlying aetiopathogenesis of the pain; and 2) Identifying clinically relevant and translational QST biomarkers that can be used to provide goal directed analgesic therapy.