Behçet's syndrome is characterized by clusters of disease expression, one of which is the coexistence of acne and arthritis. The aim of this study was to test the hypothesis that enthesopathy is increased in this cluster, having features reminiscent of acne-associated arthritis.
The study group comprised 35 patients with Behçet's syndrome who had acne and arthritis (BS-AA), 38 patients with Behçet's syndrome who did not have arthritis (BS-WA), 37 patients with ankylosing spondylitis (AS), 25 patients with rheumatoid arthritis (RA), and 25 healthy control subjects. Five entheseal sites (the superior and inferior poles of the patella, the tibial tuberosity, and the superior and inferior poles of the calcaneus) on both lower extremities were examined by 2 independent observers, using ultrasonography. A previously validated composite score was calculated for each patient. The numbers of entheseal sites giving a positive power Doppler signal in each group were also compared.
Patients with AS had the highest enthesopathy score (mean +/- SD 4.1 +/- 2.4; F [4df] = 8.43, P < 0.001) followed by BS-AA patients (3.0 +/- 1.9; F [3df] = 3.63, P = 0.015). The mean +/- SD enthesopathy scores among the remaining 3 groups were similar (for BS-WA, 1.8 +/- 1.4; for RA, 2.2 +/- 1.6; for healthy controls, 2.0 +/- 1.5 [F (2df) = 0.65, P = 0.53]). Power Doppler scores were highest for the BS-AA group (mean +/- SD 3.0 +/- 1.5; F [4df] = 15.54, P < 0.001) followed by the AS group (2.7 +/- 1.8; F [3df] = 14.38, P < 0.001), the RA group (2.6 +/- 1.8; F [2df] = 13.88, P < 0.001), the BS-WA group (1.2 +/- 1.3; F [1df] = 4.48, P = 0.038), and the control group (0.5 +/- 1.1). There was 87% agreement between the 2 observers (kappa = 0.55, intraclass correlation coefficient 0.71).
The increased presence of enthesopathy among BS-AA patients compared with that among BS-WA patients further supports the hypothesis that patients with Behçet's syndrome who also have arthritis and acne form a distinct cluster.