Estimated reading time: 6 minutes
Subedited by Dr Phil Tucak
Recognition and diagnosis of canine immune-mediated polyarthritis (IMPA) is beset by several challenges, where as little as 35% of patients can present as lame, and this is further complicated by the relative paucity of information and intrinsic rarity regarding its erosive form in patients.
A criterion for its diagnosis was formulated by the work of Bennet and Kohn as an adaptation of criteria utilised in the diagnosis of rheumatoid arthritis in people but has yet to be supplemented since 1987. Previously published articles established a propensity for IMPA to target hocks, carpi and stifles. However, the following patient may represent the first documented case for rheumatoid positive erosive polyarthritis isolated to the elbows.
Josie, a six-year-old female spey Staffordshire bull terrier presented to the Small Animal Specialist Hospital (SASH) with a history of chronic and progressive forelimb lameness.
Three years prior to referral she presented to her family veterinarian for lameness localised to both forelimbs. At the time, this was managed conservatively with a combination of rest and meloxicam for flare-ups. Progressively the discomfort worsened, and an extensive series of plain radiographs were performed by the referring veterinarian, revealing degenerative changes to both elbows.
Suspicious of degenerative joint disease (DJD), conservative management was continued with the addition of adjunctive therapies including a course of cartrophen, gabapentin 100mg q24 and rosehip oil supplementation. In the month prior to referral, further deteriorating mobility led towards a reluctance to both rise and undertake general locomotion.
On presentation at SASH, the patient was febrile and featured a grade 3/4 lameness involving multiple regions most severely affecting the right forelimb. There was resistance to palpation of the cervical spine however no signs of a neurological deficit could be appreciated.
Initial blood tests revealed a mild inflammatory leukogram comprising of neutrophils 12.86 x 10^9/L (2.95 – 11. 64)r and lymphocytes 0.68 x 10^9/L (1.05 – 5.10)r, an otherwise unremarkable blood gas and biochemical profile to the exception of a CRP >100 mg/L7 well above reference values (>10)r. While discomfort was observed on manipulation and palpation of several joints (elbows, shoulder, and hips), no gross effusion was perceived in all joints examined.
To further investigate the extent of the lameness, a CT scan was performed on the spine, forelimbs and hindlimbs. This was achieved using a pre-contrast high frequency bone reconstruction algorithm as well as pre and post medium frequency contrast soft tissue algorithm.
Imaging revealed a moderate to large amount of non-contrast enhancing synovial fluid more noticeable in the right than left elbow in conjunction with a thickened and diffused contrast enhancement of the synovium.
Concerningly there were mottled to moth-eaten lesions indicative of osteo-aggressive lysis in the epicondylar regions and subchondral bone of the humeral condyles, radial heads, medial coronoid processes and radial incisures of the ulnas. Adjacent to these lytic regions were also signs of mild irregular periosteal new bone formation. The gamut of the synovial effusion, thickening and polyostotic lesions were suggestive of either an arthritic (immune-mediated) or atypical form of a septic process. Malignant neoplasia was also considered (e.g. histiocytic sarcoma) but unlikely given the bilateral changes.
To better define the nature of the effusion, an arthrocentesis was performed on the joints identified by the CT scan (elbows, carpi, and stifles). The samples were sent externally to a veterinary pathology laboratory for fluid, cytological analysis and culture. Within both elbows was a nucleated cell population estimated at >20 x 10^9/L that was composed of 99%-97% neutrophils and 1%-3% mononuclear cells in left and right elbows respectively.
The remaining joints (stifles and carpi) on the other hand were cytologically unremarkable. Results were supportive of a poly arthropathy, albeit an erosive form as evident on both CT scan and a review of radiographs previously performed. The unlikely nature of a septic osteoarthritic process (though not entirely ruled out) was further supported by a culture revealing no growth.
By exclusion, the process suspected to have taken place was a form of erosive polyarthritis and to further confirm this suspicion, a rheumatoid factor (Rf) assay was performed and returned positive. Satisfying a criterion for the diagnosis of rheumatoid polyarthritis, the patient was then started on a combination of cyclosporine 5mg/kg q12h daily and prednisolone 2mg/kg q24h. Over the course of a month of therapeutic titration a return to normal CRP7 values <0.7mg/L (<10.0)r was noted amidst steady and considerable clinical improvement.
This case highlights that immune-mediated polyarthritis should be on the veterinary clinician’s differential diagnosis list when encountering a patient with lameness affecting multiple limbs. Moreover, erosive IMPA, while rare, can masquerade radiographically as osteoarthritis.
Jacques D, Cauzinille L, Bouvy B, Dupre G. A retrospective study of 40 dogs with polyarthritis. Vet Surg. 2002 Sep-Oct;31(5):428-34. doi:10.1053/jvet.2002.34665.
Johnson KC, Mackin A. Canine immune-mediated polyarthritis: part 1: pathophysiology. J Am Anim Hosp Assoc. 2012 Jan-Feb;48(1):12-7. doi:10.5326/JAAHA-MS-5744.
Bennett, D. (1987), Immune-based erosive inflammatory joint disease of the dog: canine rheumatoid arthritis. Journal of Small Animal Practice, 28: 779-797.
Goldstein RE, Ettinger SJ, Feldman EC, eds. Swollen joints and lameness. Textbook of veterinary internal medicine, vol. 1. 7th ed. St. Louis (MO): Sanders Elsevier; 2010:130–3. Stull JW, Evason M, Carr AP, Waldner C. Canine immune-mediated polyarthritis: clinical and laboratory findings in 83 cases in western Canada (1991-2001). Can Vet J. 2008 Dec;49(12):1195-203. PMID: 19252711;
Lewis RM. Rheumatoid arthritis. Vet Clin North Am Small Anim Pract. 1994 Jul;24(4):697-701. doi: 10.1016/s0195-5616(94)50078-0.
Caspi D, Snel FW, Batt RM, Bennett D, Rutteman GR, Hartman EG, Baltz ML, Gruys E, Pepys MB. C-reactive protein in dogs. Am J Vet Res. 1987 Jun;48(6):919-21. PMID: 3605808.
Scharf VF, Lewis ST, Wellehan JF, Wamsley HL, Richardson R, Sundstrom DA, Lewis DD. Retrospective evaluation of the efficacy of isolating bacteria from synovial fluid in dogs with suspected septic arthritis. Aust Vet J. 2015 Jun;93(6):200-3. doi:10.1111/avj.12328.
BSc BVMS FANZCVS (Small Animal Medicine)
In 2015, Dr Idowu began a two-year small animal medicine residency training program at Melbourne Veterinary Specialist Centre (MVSC). During her residency, she conducted her original research project on canine immune-mediated polyarthritis. In 2020 Dr Idowu became a Fellow in the Australian New Zealand College of Veterinary Scientists. She has a special interest in infectious diseases, hematology, immunology and cardiology.
Dr Steven Sath BVSc
Dr Sath is a 2010 Melbourne University graduate who spent almost a decade in general practice. He is currently completing a small animal rotating internship at Small Animal Specialist Hospital (SASH) on the Central Coast in NSW, and he has a keen interest in internal medicine and oncology.