Read the German translation: Durch Schmerzen ausgelöste Verhaltensstörungen: Symptome der Osteoarthritis

Introduction^{1,7,8,9,12,14,15}

It is proven, that animals perceive pain and suffer from it like humans. Effective analgesia can reduce stress reactions, peripheral and central sensitization. Also, an adequate individual pain therapy is important, to prevent the development of pain memory especially after surgery but also in patients whose pain is caused by osteoarthritis (OA). The problem of an adequate therapy is that before it starts, pain has to be diagnosed. Every patient demonstrates pain in a unique way, especially in OA. If a patient does not show typical signs of pain, this does not mean that the animal is not in a painful situation. It is well known that animal nociception and perception of pain proceed in the same way as humans. The problem in animals is that a special pain-related behavior does not exist, also animals cannot document their degree of pain nor can they tell it to the veterinarian. Therefore pain assessment in animals is not so easily done. An exact observation of the patient is absolutely necessary and the difficulty in assessing pain does not mean that treatment of the patient is not necessary. The opinion that postoperative pain has a protective function is wrong and not longer tolerable. Pain therapy should start as early as possible, in order to prevent pain development. The longer pain exists the more difficult pain therapy is. Chronic pain in OA patients is often difficult to diagnose and to treat because objective and clear signs are not seen very often. In doubt, a pain therapy should be started similar to human beings. In some cases a diagnostic pain therapy could be useful. But before starting this type of therapy one should be secure that no other diseases exist. The special pain related behavior in animals depends on many factors like species, age, breed, sex, personality, and the severity and duration of pain. The often inconspicuous signs of pain may be an innate protective mechanism to prevent an enemy from recognizing to be an easy prey.

Chronic Pain in Osteoarthritis^2-11,13

Chronic and relapsing pains are the main symptoms in OA. Acute flares are due to inflammation in the diseased joint, which is the reason for pain. Every flare is activating peripheral and central sensitization. In consequence hyperalgesia and allodynia could develop in the patient. Typical signs of OA are not seen every time; therefore pain in OA patients is sometimes called a "silent problem".

Chronic pain due to OA is often difficult to detect because the signs are not as clear as in acute painful situations. Often only subtle changes in behavior are an indicator for OA pain, and in some cases OA pain is first recognized after a diagnostic therapy. Chronic OA pain often develops over a long time, it is no sudden event. Additionally OA patients are often old dogs and cats which are obese and in consequence can show dyskinesia. The owner thinks that these slow changes in behavior of the pet are age related, and does not realize that this is a disease and sign of OA. Lameness, disturbance of motion or painful reactions of the animal mostly are not coming to the fore in animals with chronic pain of OA but subtle, individual changes in behavior could be recognize in the patient. It is also possible that animals with changes in their behavior are first presented to a behaviorist. If the behaviorist is diagnosing OA and a therapy (pain therapy and/or surgery and/or multimodal therapy) starts, the changes in behavior often disappear.

Changes in behavior, which are related to OA, are more often seen in cats than in dogs. Additionally this behavioral manifestation of chronic pain is not associated with an organic disease. A reason for this is the insufficient evaluation of pain because behavior changes are not checked, and are very difficult for the veterinarian to detect. Cats can adept their movement sequences to their diseased OA joint. Cats also normally are not put on the leash and so lameness is often unnoticed. To assess pain in cats with OA special views are put on changes in behavior. These changes could be delicate and individual, and these cats can react very special in the practice of the veterinarian. Cats often have additional stress and anxiety, and it is often not easy to distinguish between stress, anxiety and pain. In these cases a diagnostic therapy, after a complete examination and the exclusion of other organic disease, could be helpful in diagnosing OA.

Diagnose of OA Related Behavioral Manifestation of Pain

The behavior of an animal which is suffering from pain in the veterinarian's practice can differ from the behavior at home. This is the reason why a special anamnesis can be very helpful, because very often the owners have not recognized the often subtle changes in the behavior of their dog or cat, and don't connect this to a disease. On the basis of the diverse possibilities of behavioral manifestation of pain, which also could be very different in dogs and cats, a lot of special question could be necessary to diagnose OA in these patients. But on the other hand only a person who knows the routine pattern of behavior of the animal can assess the changes.

Pain in OA patients can appear during rest, but often pain appears during the first steps after rest or after a long exercise. Pets which are suffering from OA pain are often obese because they don't move much and they get normal or sometimes more food than they really need. Special questionnaires could be very useful in the daily routine to evaluate if an animal is suffering from pain and/or shows a behavioral manifestation. If X-rays are used to diagnose OA and a painful situation we must keep in minds that the degree of the radiologic signs of OA normally doesn't correlate with the degree of pain.

Dog

Pain related behavior in dogs could be 1) anxiety, 2) decreased social interaction, 3) obsequiousness, 4) aggressiveness, 5) decreased activity, 6) drop in performance, 7) reduced temperament, 8) abnormal body position, and 9) abnormal gait. Also 10) yowling, and 11) self-mutilation could be signs of behavioral manifestation of OA related pain. Aggressiveness and defensive posture to manipulation are sometimes seen if the animal is brushed. Also avoidance posture could be realized if the dog 12) should jump into the car, 13) the dog cannot jump any longer on the sofa bed or 14) if the bell is ringing the dog does not walk to the door. 14) Stiffness in the morning and unwillingness to stand up could be signs of behavioral manifestation of OA related pain. Naturally also the classical signs of OA like lameness after exercise and lameness after rest could be find additionally.

Cat

1) Aggressiveness and 2) anxiety are the most usual behavioral signs of OA related pain. But also 3) sleepiness, 4) and vocalization could be observed. 5) Changed social interaction like reduced willingness to play or reduced activity or ignoring the cat tree could be signs of pain. Also 6) reduced or 7) increased grooming are possible indicators for pain. Therefore dermatological problems could be the first obvious signs of OA for the owner. Reasons for this behavior are hyperalgesia or allodynia which develop during the process of sensitization. 8) Cats try to escape in case of manipulation or 9) they sometimes go into hiding if they expect a painful manipulation. 10) Weight loss is a possible sign of pain if the cat cannot reach food which is offered in a higher position. 11) Cats could refuse the litter box and lose their house training if it is painful for them to use the litter box.

Because of the multiple possible changes in behavior in cats, which are suffering from pain, it is very useful to know the physiological day of a cat. Cats normally sleep ca. 9.5h, rest for ca. 5.3h, are hunting ca. 3.6h, groom ca. 3.5h, walking without hunting ca. 0.6h, are invisible ca. 0.58h, are eating 0.55h, and 0.33h they are doing other things. In addition to abnormal behavior also the results of the clinical examination and the X-rays have to be evaluated. The consideration of the results of these three evaluations is also called triangulation.

Clinical Conclusion^7,8,11,14,15

Especially chronic OA related pain is often not clearly demonstrated and behavioral manifestations of pain is possible. An interactive and no interactive behavior pain assessment is very useful especially to evaluate the chronic OA pain. To diagnose these behavioral changes a "Health Related Quality of Life Scale" could be very helpful. This questionnaire evaluates physical, behavioral and social factors. The owner can classify questions like "is your pet behaving normal" with regularly, sometimes, or rarely. The results of this classification of quality of life (QOL) must be used in conjunction with clinical examination of the animal and all other pain scales which have been used. This procedure could help to optimize animal well-being.

References

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15. Wiseman-Orr, et al. Am J Vet Res 2004; 65 (8): 1077

16. Weitere Literaturstellen auf Nachfrage bei der Autorin erhältlich.