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Veterinary Forum July 2007 (Vol 24, No 7)

Diagnostic Dilemma: "Disappearing Joints"

by Susan Hodge, DVM, A. D. Elkins, DVM, MS, DACVS, Aaron Wehrenberg, DVM

    Taiga, a 7-year-old, 9-lb, spayed shih tzu, presented for evaluation of hindlimb weakness and reluctance to use her hindlimbs. According to the owner, this behavior had started about 6 months after surgery was performed on the left stifle and had gradually progressed for the past 2 years. At this time, Taiga preferred to crawl across the floor on her belly like a centipede.

    Review of her medical records indicated that Taiga had been seen several years earlier for evaluation of left hindlimb lameness that had been associated with the stifle joint. At that time, partial rupture of the left cranial cruciate ligament was diagnosed. Because she was small, Taiga was treated using an extracapsular stabilization technique (lateral deAngelis suture of 20-lb nylon). The dog had recovered from surgery well but had become reluctant to walk on her hindlimbs about 6 months later. There was no known history of trauma; Taiga simply seemed to have become progressively weaker in the hindlimbs and had become reluctant to stand or walk.

    Referral findings

    A thorough physical examination, including musculoskeletal and neurologic evaluations, was performed. The dog walked well on her forelimbs but would not bear weight on the hindlimbs; instead, she wiggled across the floor. The neurologic examination found no abnormalities, and no pain was elicited in the neck and back regions.

    Palpation and manipulation of the dog's hindlimbs revealed increased laxity and crepitus of the digits and hocks, good stability in the stifles with no loosening of the nylon suture in the left stifle, and no cranial drawer motion in the right stifle. Manipulation of the hips revealed no pain, moderate crepitus, and normal range of motion. Further evaluation of the forelimbs revealed both laxity and crepitus in the digits, carpus, and elbows. The remainder of the physical examination was unremarkable.

    Because of the involvement of multiple joints, concern grew that Taiga had a systemic disease process, such as polyarthritis, polyarthropathy, or severe degenerative joint disease. A workup, including blood work and radiography, was recommended.

    The workup

    With the patient under sedation, radiographs of the stifles (Figure 1A) were taken and compared with previous views (Figure 1B) that had been obtained before surgery of the left stifle. The current radiographs revealed severe erosive disease, with substantial loss of normal bone structures and collapsed joint spaces (Figure 1A). Unusual radiographic changes were apparent in the hip and shoulder joints where both the femoral and humeral heads had an apple-core appearance, collapsed joint spaces, and evidence of substantial remodeling or flattening of the bones (Figure 2 A and 2 B). The distal limbs, including the digits, carpus, and tarsus, appeared to be affected most significantly, with substantial bone loss and increased laxity in the distal joints (Figure 3).

    Based on the initial radiographic evidence of severe erosive disease affecting multiple joints, there was concern that Taiga was suffering from an advanced case of rheumatoid arthritis (RA). At that time, none of the joints was palpably swollen.

    Because of the substantial collapse of the joint spaces, joint taps would likely be unrewarding in obtaining a definitive diagnosis. Collecting syno-vial biopsy specimens and conducting blood tests were discussed with the owner as alternatives for obtaining a diagnosis.

    Blood was submitted for both a complete blood count (CBC) and an autoimmune panel, including direct Coombs' testing, antinuclear antibody (ANA) titer, and rheumatoid factor (RF) test. The results of the CBC were unremarkable. The direct Coombs' and RF test results were negative, but the ANA titer was positive at 1:64 (normal: <1:16). This positive result suggested that Taiga was suffering from an autoimmune disease. Based on the blood test results and radiographic evidence of severe erosive polyarthritis, either RA or systemic lupus erythematosus (SLE) was suspected.

    Discussion

    Differentiating between RA and SLE based on the results of blood testing alone can be confusing. Both the ANA and RF tests in dogs are not perfect because they identify circulating levels of antibodies that can be elevated in patients affected by other disease conditions, including chronic infections, inflammation, or neoplasia.1,2 It is not entirely known whether it may be more accurate to measure these factors on samples obtained from serum or directly from the joint fluid.

    In addition, it has been shown that only about 70% of dogs with RA have tested positive on the RF test. Thus, a negative result does not prove that a patient does not have RA.3 Circulating levels of antibodies have been known to fluctuate with other disease conditions and may have been low in this dog at the time of sampling. Sufficient research has not been conducted in dogs with these autoimmune conditions to know whether antibody levels plummet late in the disease process.

    Reaching a definitive diagnosis may become an academic endeavor regarding identifying which autoimmune disease is present, as most autoimmune conditions are treated with immunosuppressive agents. It is vital, however, to know whether other infectious or neoplastic conditions are present before initiating this therapy.

    Elaborate criteria for identifying SLE and RA in human patients have been identified. These criteria have been carried over to veterinary medicine, but they may not be as helpful in classifying these same diseases in dogs3-5 (see the box). Using the established criteria, Taiga does not fit into either classification scheme; however, she does display significant physical and radiographic disease. Based on involvement of multiple joints and radiographic evidence of erosion around the joints, Taiga's condition supports a diagnosis of RA versus SLE despite the blood test results.2,5 In addition, because Taiga is a small-breed dog, it is more likely that she has RA than SLE, which is typically diagnosed in collies, shelties, and German shepherds.

    RA is a debilitating and frustrating disease to treat.3 The erosive destruction of bone often progresses despite treatment.1,3 Because Taiga had presented in the advanced stages of disease, the possibility of improving her condition with immunosuppressive therapy was discussed. The owner chose not to pursue additional diagnostic testing, such as obtaining joint biopsy specimens, because doing so likely would not change the course of the disease process or treatment recommendations. Taiga is receiving an NSAID and intermittent opiate administration for pain.

    Reviewer Comment

    This case demonstrates that certain medical conditions, such as RA and SLE, rely on accumulation of various criteria to obtain a presumptive or definitive diagnosis rather than on a single gold-standard diagnostic test. Other examples of difficult-to-diagnose medical conditions include separation anxiety, many tick-borne diseases, disseminated intravascular coagulopathy, multiple myeloma, and inflammatory mammary carcinoma, to name a few.

    Read about the Basics of Rheumatoid Arthritis .

    Drs. Hodge, Elkins, and Wehrenberg are affiliated with Veterinary Specialty Center of Indianapolis, Ind. All three authors are frequent contributors to Veterinary Forum, and Dr. Elkins is a member of the Forum Editorial Board.

    1. Ettinger S, Feldman E (eds): Textbook of Veterinary Internal Medicine, ed 5. Philadelphia, WB Saunders, 2000, pp 79-80, 1879, 1882.

    2. Tilley L, Smith F: The 5-Minute Veterinary Consult, ed 2. Philadelphia, Lippincott, 1997, pp 1100-1103.

    3. Fossum T(ed): Small Animal Surgery, ed 2. St. Louis, Mosby, 2002, pp 1041-1042.

    4. Villiers E, Blackwood L (eds): BSAVA Manual of Canine and Feline Clinical Pathology. Gloucester, British Small Animal Veterinary Association, 2005, p 360.

    5. Thrall D (ed): Textbook of Veterinary Diagnostic Radiology, ed 3. Philadelphia, WB Saunders, 1998, pp 179-180.

    6. Burk R, Ackerman N: Small Animal Radiology and Ultrasonography, ed 2. Philadelphia, WB Saunders, 1996, pp 513-514.

    7. Boothe D: The new nonsteroidal anti-inflammatories: Meet the cox's. Proc Midwest Vet Conf:2007.

    References »

    NEXT: Distemper still causes significant disease in dogs

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