Chronic Pain Assessment in Dogs
Assessment by Owners
Musculoskeletal pain (e.g., OA) is the most common form of chronic pain in dogs and where most work has been performed to understand how to measure it. Owners can detect the presence of pain in dogs by comparing normal and abnormal behavior, but they may contextualize these signs and delay action for several months.20,21 Owner responses to open questions—such as “how is he (or she) doing?”—can raise red flags that will warrant more specific questions. Red flags can also be raised using screening tools. These are not specific for a given condition, although they may be targeted at a specific condition. They allow a conversation focused on possible conditions. Once a condition is highly suspected or confirmed, several questionnaires are used to evaluate chronic pain. Available questionnaires are mostly focused on canine OA. Questions relate to demeanor, mobility, and lifestyle, capturing information in a consistent and repeatable manner. The most widely used questionnaires are the Canine Brief Pain Inventory (CBPI, 11 questions)22,23 and Liverpool Osteoarthritis in Dogs (LOAD, 23 questions).24,25 The Sleep and Nighttime Restlessness Evaluation (SNoRE) questionnaire focuses on sleep quality.26 These questionnaires, which can be downloaded and used at no cost, assume the presence of OA but may also help diagnose other conditions. The client-specific outcome measures (CSOM) assessment is a questionnaire that relies on the veterinarian to define a set of activities that are not being performed normally and that are specific to a pet. These “client-dog dyad–specific” questions are followed over time to assess response to therapy.27 Client questionnaires have been used to support the regulatory approval of several pain medications for dogs. Although these instruments remain subject to bias, they are validated to varying degrees and provide useful and actionable information. One of their most powerful features is that they standardize the questions that are posed to owners, allowing trends over time to be captured more accurately.
Clinician Assessment of Pain in Dogs
Observation is a critical part of the veterinarian assessment of chronic pain. Signs of pain can be observed when a patient is resting, standing, moving at a walk or a trot, or doing functional activities such as climbing steps. At rest, awkward limb positions may indicate the presence of joint pain; for example, dogs with elbow joint pain may supinate their forelimbs and flex their carpus. When standing and moving, dogs shift weight away from a painful limb, and such postural abnormalities can be observed in the examination room if the animal is given time to relax. Recently, a staging tool has been proposed for canine OA,28 which incorporates both owner and veterinarian assessments. The veterinarian assessments include observation of posture and motion as well as results from the hands-on evaluation. A “tucked up” appearance can be an indicator of abdominal pain, and postural straining can be an indicator of lower urinary tract or lower gastrointestinal tract pain. When pain is intermittent or associated with specific activities that are not reproducible in the clinic, pictures or videos collected by the owner and reviewed by the veterinarian provide useful pain-related information.
Palpation is the most widely used clinical method to detect pain in dogs, even if surprisingly few studies have evaluated its sensitivity and specificity.29
Medical imaging is used to confirm the presence of a suspected problem. Joint pain on palpation and radiographic signs of OA often correlate poorly.19 Because of that discrepancy, radiographs only confirm the cause of joint pain detected on palpation rather than assume that all radiographic abnormalities represent a source of pain.