Background and objectives: Patients with psoriatic arthritis (PsA) as well as those with synovitis, acne, pustulosis, hyperostosis, osteitis (SAPHO) syndrome share some common features, and in fact, for many authors the SAPHO concept fits well into the broader concept of PsA. However, some clinical features are unique to the SAPHO syndrome, and in the other hand, these patients do not show the known association between the HLA-B27 antigen and the spondyloarthropathies. To date, there are no studies comparing the immunogenetic profile of these two conditions, so the main objective of the present report was to analyse whether or not both entities may share the same genetic basis.
Patients and methods: All patients with SAPHO syndrome (n=25) seen in a single university hospital from 1985 to 2005 were recruited and followed up in standardised manner in order to study their main characteristics and HLA profile. The HLA-Cw6, DR and B27 antigen distribution of these cases was compared to that of 50 patients with psoriasis vulgaris, 120 with PsA, and 170 healthy blood donors. PsA patients were classified in accordance with their predominant pattern observed in the last 5 years of disease evolution. Odds ratios (OR) values were calculated to measure the strength of the association between HLA antigens and disease, while the statistical significance of the association was assessed with a two-tailed Fisher's exact test. P<0.05 values were considered significant.
Results: No association was found between HLA-Cw6, B27, or DR antigens, and SAPHO syndrome. HLA-Cw6 was strongly associated with psoriasis, OR 12 (95% CI: 5.6-26, p<0.0001) and PsA, OR 10 (95% CI: 5.4-19.5, p<0.0001), however this antigen was equally distributed among the three articular categories of PsA. HLA-DR4 was found under-represented in PsA patients compared to controls, OR 0.4 (95% CI: 0.2-0.7, p=0.002). HLA-DR7 correlated well with psoriatic oligoarthritis, OR 9.6 (95% CI: 2.9-28, p<0.0001), HLA-DR8 was found associated with polyarthritis, OR 6.7 (95% CI: 2-25, p=0.002), while HLA-B27 was over-represented in psoriatic spondylitis, OR 10 (95% CI: 3.3-25, p<0.0001).
Conclusions: Psoriasis/PsA and SAP-HO syndrome show a different immunogenetic background, however the genetic basis of SAPHO syndrome remains unknown.