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

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Until very recently, pain in people was considered to be a single uniform entity; the nature of the pain experienced by an individual was considered to be similar regardless of the underlying cause. However this concept has now been challenged, which of course fits with everyone's own unique experience of pain resulting from tissue injury, trauma or surgery. The nature and quality of pain caused by each disease condition is different and reflects the underlying changes in the sensory system responsible for causing pain. For example, people may show differing changes in sensitivity to warm or cold stimuli, reflecting different underlying aetiologies or mechanisms of pain. In man this has led to personalized therapy for pain. It is now possible, in people, to identify distinct pain patterns (termed pain phenotype) that relate to distinct changes in sensory processing and target these underling changes in sensory processing with specific drugs. This has resulted in improved pain management in people in chronic pain. The aim of this current proposal is to translate the concept of personalized pain therapy from people to dogs and subsequently increase our capability to provide adequate pain relief to dogs suffering from chronic pain. A very common cause of chronic pain in dogs is osteoarthritis. We currently assume that all dogs with osteoarthritis suffer similarly from pain and show similar altered sensitivity to sensory stimuli such as heat and pressure. However, in people suffering from osteoarthritis, different types of pain associated with different sensory sensitivities are recognized, and these distinct pain patterns are likely associated with different underlying changes in the sensory nervous system. We predict, given the similarity between the disease of osteoarthritis in dogs and man, we will be able to identify similar distinct pain patterns in dogs suffering from osteoarthritis. We will study pet dogs with osteoarthritis, recruited through liaison with veterinary surgeons. The dogs will benefit from a detailed clinical assessment of their osteoarthritis with follow up advice about optimising their pain management, provided by European Specialists in canine osteoarthritis and animal pain management.A major discriminator in the underlying pain mechanisms is whether the pain results primarily from changes in sensory processing in the peripheral nervous system (i.e. in the processing of sensory stimuli localised to the site of the disease process, in the case of osteoarthritis this would be the affected joint) or whether pain is caused by changes in the periphery (the joint) and in the central nervous system (i.e. the spinal cord and brain). Once pain is associated with peripheral AND central nervous system changes it becomes much more difficult to manage effectively and also requires different pain management strategies, for example different types of pain killing drugs are necessary. We will use a simple, validated experimental paradigm to distinguish whether both peripheral OR peripheral AND central changes in sensory processing are present in individual dogs with osteoarthritis. This test will be carried in dogs that are anaesthetised and therefore unaware. Subsequently, in awake animals, we will map the individual pain pattern or pain phenotype to allow us to link pain mechanism with clinical pain expression. This will be achieved by testing sensitivities to warmth, heat, cold and pressure stimuli. Ultimately, we hope that a veterinary surgeon will be able to examine a dog with osteoarthritis in their clinic, and determine using simple and non-invasive tests, their pain phenotype, and use this information to derive knowledge of the underlying pain mechanisms. This will allow the veterinary surgeon to target or personalize pain medication to the patient, with the goal of improved pain management and the lifelong welfare of the individual animal.