To investigate the value of synovial fluid analysis in predicting the outcome of psoriatic monoarthritis.
In synovial fluid from knee joints of 18 patients with psoriatic monoarthritis lasting less than six months, white blood cell count, acid phosphatase, lysozyme, and interleukin (IL)-1 beta were determined. ESR and serum C reactive protein were also measured. To define the outcome, the patients were monitored for at least three years and then subdivided into those with polyarthritis and those without.
Among the blood and synovial fluid indices considered, synovial fluid IL-1 beta was the only variable which differed between the patients who developed polyarthritis, within three years and those without polyarthritis after this time, at 20.82(SD 8.79) v 4.19(4.73) pg ml-1, P < 0.0001). A correlation was found between synovial fluid IL-1 beta concentrations and the number of affected joints after three years (r = 0.739, P < 0.0001).
Determination of synovial fluid IL-1 beta at disease onset may be useful in revealing the outcome of psoriatic monoarthritis since, among the variables considered in our study, this was the only one capable of predicting the evolution of monoarticular psoriatic arthritis to polyarthritis.