Outcome Assessment in Treatment of Osteoarthritis Pain and Lameness in Dogs and Cats, Where Are We Now?
Osteoarthritis (OA) is a slowly progressive, degenerative, and dynamic disease which causes significant pain, lameness, and disability in our canine and feline patients. The incidence and prevalence of this disease in dogs and especially cats is probably underestimated. With the growing awareness of the pain and dysfunction caused by OA in our patients, a large number of purported therapeutic agents have been introduced and used for the treatment of canine and feline OA with varying levels of effectiveness. These therapeutic agents vary widely regarding their documented efficacy and safety. This discrepancy creates a difficult situation for clinicians who want to make an informed clinical decision with their clients and for their patients. One of the biggest obstacles in the evaluation of these treatments is the wide range of clinical testing methodologies that have been used to assess them. Many of these methods are very weak and have not been validated. Thus as we push forward using new therapies to treat the pain of OA, we must take great care in assessing not only these therapies but also the methods by which these therapies are evaluated.
Recent advances have been made in understanding the molecular mechanisms of pain yielding new important information that is now being incorporated into clinical pain management at all levels. Yet despite all the new information, it is humbling to realize how little we do know about pain and our abilities to intervene effectively. In the management of chronic pain caused by OA in dogs and cats, two common false assumptions are made by clinicians. The first is that one drug, at one dose, will work for all patients and second is that pain management is an "all or none" occurrence. Remember each patient may require different drugs, doses or even a combination of therapies to maximize pain relief. A clinician should work toward the goal of pain reduction and subsequent improved patient comfort. Thus one must ask the question, how do we know our treatments are working to alleviate pain, especially chronic pain? Certainly, the drugs which are approved by formal regulatory review have some efficacy data supporting their use against pain but think of all of the off-label and alternative medications we commonly give to our patients. How confident are we that they work on our particular patient? As clinicians, we need to ask this question every time we prescribe any products to treat pain.
Thus quantitative measures of chronic pain that are valid and reliable in clinical patients are crucial. Studies designed to test the efficacy of interventions intended to decrease the chronic pain of OA have relied heavily on a objective gait analysis (kinetic [force plate] and kinematics) and subjective analysis (veterinarian's assessment of lameness). When properly collected, objective gait analysis data provides an objective measure that can be reliably monitored over time. This methodology is however extremely time-consuming process, and requires specialized equipment. Furthermore, these data only evaluate an animal in a specific time point of a given day and outside of its typical environment. Subjective methods of analysis historically have been very crude, not reliable and have not been validated. However, recent works by several research groups have begun to show exciting new subjective scoring systems that may prove to be very useful in our efforts to manage the pain and dysfunction associated with OA. These evaluation systems include specific owner derived evaluations of their pets in their normal surroundings.
Currently we are moving into a potentially exciting time in the treatment of OA in small animal medicine. We may soon have clinical tested products that we have combined reliable and valid owner based evaluations, veterinarian evaluations and objective gait analysis to substantiate or refute their purported positive effects on the pain and dysfunction of OA in our patients. Please remember however, that these new evaluation tools are only part of the solution. Clinical studies must still be carefully designed with sufficient numbers of animals included to insure reliable data that can be used by clinicians with confidence.