Effect of repeated arthrocentesis on cytologic analysis of synovial fluid in dogs.

BACKGROUND: Serial arthrocentesis and synovial fluid examination can be used to monitor treatment efficacy in immune-mediated polyarthritis (IMPA), but whether this procedure induces inflammation that interferes with test result interpretation is unknown. OBJECTIVES: The aim of this study was to determine the effect of repeated arthrocentesis on synovial fluid cytology in healthy dogs. ANIMALS: Nine healthy client-owned dogs. METHODS: Prospective study. Arthrocentesis was performed under sedation on 4 joints (both carpi, 1 tarsus, 1 stifle) on each dog every 3 weeks, a total of 4 times. Automated cell counts were done on stifle fluid, smears were made, and differential cell counts done on smears from all joints. Slides were evaluated microscopically for erythrocyte numbers, total nucleated cell count, differential cell count, and cell morphology. Data were analyzed by 2-way analysis of variance. RESULTS: A total of 144 synovial fluid samples were examined. Repeated arthrocentesis was not associated with increases in synovial fluid neutrophil numbers. Mild mononuclear inflammation was detected in 13 samples from 6 dogs. CONCLUSIONS AND CLINICAL IMPORTANCE: Serial arthrocentesis at 3-week intervals can rarely be associated with mild mononuclear joint inflammation, but does not appear to induce neutrophilic inflammation, at least in healthy dogs, and can be useful to monitor treatment response in canine IMPA.