[Characteristics of synovial fluid in patients with juvenile idiopathic arthritis]

Synovial fluid (SF) analysis is an important tool for the diagnosis of patients with juvenile idiopathic arthritis (JIA).

A retrospective analysis was carried out of cytological features of SF samples obtained from patients with JIA during the period 2008-2016.

A total of 102 SF samples from 59 patients were analysed. JIA was more common in females (66%). The most frequent form was persistent oligoarticular JIA (52.5%). The median age at onset was 5 years (IQR 2.4-11.8). SF usually showed an inflammatory pattern (median white blood cells count 11,757/mm³; IQR 4,543-18,800), with a predominance of polymorphonuclear (PMN) cells (61%; IQR 30-75). Eight patients (14%) had white blood cells counts of less than 2,000 cells/mm³, with predominance of mononuclear cells (80%), whereas 3 patients (5%) had white blood cells counts higher than 50,000 cells/mm³, with a predominance of PMN cells (90%). Synovial white blood cells count did not show significant differences among the different forms of JIA. The median synovial white blood cells count in ANA-positive patients was 20% lower than in ANA-negative (9,340 vs. 11,600/mm³; P=.23). The proportion of PMN increased with increasing levels of ESR (P<.001) and/or CRP (P=.03). No significant correlation was found between JADAS-10 and synovial white blood cells count (P=.4). SF obtained from different joints in simultaneous arthrocentesis showed a significant correlation P=.001).

SF from JIA patients usually had inflammatory characteristics, although 19% of the patients showed white blood cells counts below 2,000cells/mm³ or higher than 50,000cells/mm³. SF cell count was non-significantly lower in ANA-positive patients, and the proportion of PMN increased with increasing levels of ESR/CRP.