Degenerative joint disease in cats (Proceedings)

Cats are notorious for concealing pain. In contrast to dogs, they rarely vocalize in response to ain unless pushed to the limit. If they are pushed to the limit, they may explode and become aggressive. Many of the manifestations of pain in the cat are behavioral. Subtle changes in behavior can indicate quite severe pain. It is important to become thoroughly familiar with the behavior of a given cat in the home and the hospital.

Pain can them be assessed by deviations from the norm. At home, the owner may observe decreased appetite, grouchy behavior, urinating and defecating outside the litter box, and reduced movement between vertical perching sites. Weight loss may occur because the cat isn't feeling well enough to eat, or because the cat ishaving trouble accessing food that is placed on a high surface. The grouchy behavior is often recognized by owners because the cat doesn't want to be picked up or interacted with. There is little to no play behavior. Litter box accidents can happen because the cat can't easily get in and out of the litter box or doesn't feel well enough to go to the litter box. The cat may have trouble assuming the correct stance for d defecation or urination, resulting in constipation or accidents. A cat that normally likes to rest in a window sling or on the back of the couch may have trouble getting to the normal location and find a sunny spot on the floor instead. If the cat does get to the couch or on a high bed, it may have an accident because it doesn't want to jump down to urinate in the litter box.

Other indications of pain are poor grooming and matted hair coat. If the cat loses flexibility and can't turn around to groom, mats will form over the back. If the source of the pain is orthopedic disease, the gait may become stilted and the cat may assume very awkward positions when jumping up or down. The owner may notice that the cat is less willing to move and spends even more time than usual in a huddled, sitting position. While it is normal for cats to sleep a lot, it is not normal to cats to sit awake in a sternal, crouched position for long periods of time without moving. Limping is a rare indication of pain in the cat. Occasionally, a cat will have one painful limb and exhibit an obvious limp, but more commonly, the pain is from bilateral orthopedic disease, spinal disease, or a nonorthopedic cause. Cats can easily shift their weight between limbs and can compensate for limb pain without an obvious limp. Even when they do limp, an obvious head bob or lack of weight bearing is rarely seen. If the cat can be observed freely moving in a familiar environment, it may be possible to detect the weight shift between the fore and hind limbs or between sides.

Unfortunately, once the cat is in the clinic, they will rarely move freely and are difficult to observe.One of the best ways to get accurate observations of cats in their home environment is to have the owner video the cat. Any awkward motions or abnormal behaviors can be captured while the cat is not stressed by hospitalization.

Musculoskeletal disease (e.g., degenerative joint disease, osteoarthritis) is less well recognized in cats than in dogs. However, it is surprising how often degenerative joint disease is discovered as an incidental finding on feline radiographs. Sometimes, degenerative joint disease may be a cause of the cat apparently "slowing down with age". In these cases, treatment may markedly improve the cat's mobility and general well being.

Ostochondritis dessicans occurs in cats but is often not recognized in the early stages when surgical intervention is helpful. Fragmented coronoid process is another disorder often overlooked until severe DJD is present. Hip dysplasia is very common in cats and will often be a significant cause of pain and decreased mobility with age. The stifles may be affected in cats with hip dysplasia and medial patellar luxation is a common associated finding in these cats. Cruciate ligament tears most often involve avulsion of a small fragment of bone from the distal tibial plateau attachment of the ligament rather than via a central tear as in dogs. This avulsion may be seen as a small joint mouse on radiographs. Early recognition and joint stabilization can prevent severe DJD if either of these stifle problems are recognized early in the course. Tarsal DJD occurs rarely and may cause fusion and reduced range of motion in the joint. Lumbosacral instability and compression may be a reason for hypersensitivity and pain in the LS and dorsal pelvic region of cats. Because pain is elicited when the cat postures to eliminate, litter box aversion and ectopic elimination behaviors may be a manifestation of this problem. True vertebral disc protrusion is uncommon in cats but will cause signs similar to dogs.

Environmental approaches to improving comfort in cats include providing ramps to allow easier access to higher locations such as beds, cat trees, and windowsills. Food and water bowls should be placed on the floor or some other more readily accessible location. Litterboxes with low sides will make it easier for the cat to enter and leave the box. Providing a source of heat that the cat can move on and off voluntarily will often be attractive to cats with DJD and provide a source of comfort particularly in cold weather.

Unfortunately, we do not have many choices for pain and inflammation control for osteoarthitis in cats because they are intolerant of many NSAIDs. Agents that have been recommended include Adequan [Equine formulation] (0.15 ml/10 lb BW IM once weekly x 4-6 weeks, then q2-3 weeks), Cosequin, and other nutraceuticals. The NSAID, meloxicam (Metacam®), is not approved for oral use in the cat in the US at this time, however, it has been used safely and successfully in cats in other countries for several years. The dose for cats is 0.1 mg/kg PO q24h for 1-2 days loading dose then 0.1 mg TOTAL dose q24-72h. Try to reduce the frequency of administration to the minimum needed to keep the cat comfortable. Side effects of NSAIDs include vomiting, anorexia, and GI ulceration and owners should be warned to stop medication immediately and contact you if any of these signs occur.

Buprenorphine (0.01-0.03 mg/kg q6-12h sublingual), tramadol (12.5 mg (1/4 of 50 mg) PO q12h), and amantidine ( 3 mg/kg PO q24h), can be used in cats that do not tolerate NSAIDs or as an adjunct to NSAIDs. Gabapentin (3 mg/kg PO q12-24h) may be most helpful for cats with LS instability and neurologic pain.

Reference

1. Romans CW, Gordon WJ, Robinson DA, Evans R, Conzemius MG. Effect of postoperative analgesic protocol on limb function following onychectomy in cats. J Am Vet Med Assoc. 2005 Jul 1;227(1):89-93.

Pain scale below from Elizabeth M. Hardie, DVM, PhD, Diplomate ACVS