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A dorsopalmar view radiograph of the right carpus of a seven-year-old, male domestic shorthair cat which presented with a three-month history of lameness, weight loss and lethargy. On clinical examination the cat was pyrexic with bilaterally warm, swollen, painful carpi and hocks. Crepitus was elicited on manipulation of all of these joints. Significant muscle wasting was noted in both fore and hindlimbs.
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| Describe the radiographic abnormalities. | There is substantial soft tissue swelling that is most pronounced on the lateral aspect of the carpus. Periosteal new bone is visible on the styloid process of the ulna and on the medial styloid process of the radius. In both instances the new bone extends beyond the margins of the joint. The antebrachiocarpal joint space is irregularly widened and there is subchondral bone loss of the radiocarpal bone and of the distal radius. An enthesophyte is visible at the base of metacarpal bone V. |
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| What is the most likely diagnosis? | The most likely diagnosis is periosteal proliferative polyarthritis. This is an immune-mediated erosive arthropathy that occurs more commonly in cats than dogs. This condition is generally bilaterally symmetrical and frequently affects the hocks and carpi. Typically, marked periosteal, periarticular new bone formation is seen radiographically. Other characteristic changes include loss of subchondral bone and enthesopathy. |
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| What further tests should be performed to substantiate the tentative diagnosis? | Synovial fluid analysis and histologic examination of the synovial membrane should be performed to establish a definitive diagnosis. The synovial fluid will typically have decreased viscosity and contain increased numbers of white blood cells, predominately polymorphonuclear cells. Histologic examination of the synovial membrane demonstrates a predominantly mononuclear cell synovitis. The disease mimics rheumatoid arthritis except that fewer joints are affected, there is extensive periarticular new bone, enthesopathy may occur and there is an absence of circulating rheumatoid factor. |
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