Psoriatic arthritis as a mountain

The concept of psoriatic arthritis (PsA) is not yet universally accepted. Indeed, few of the features said to be characteristic for PsA are pathognomonic, and a same patient can be classified as RA, SpA or PsA depending on the physician seen. The heterogeneity of PsA, the lack of significant differences in early-arthritis with and without psoriasis, and a pathogenesis somewhat different in PsA and psoriasis, also argue against the originality of PsA. Nevertheless, although PsA is possibly "just" a syndrome depending on the combination of numerous co-factors (perhaps shared with SpA and/or RA), its more achieved forms deserve to be segregated from other SpA and RA. Indeed, PsA best bridges the gap with SAPHO syndromes. Moreover, the profile of synovial cytokines seems somewhat different in PsA as compared to RA and SpA, and a special pattern of vascularisation has been confirmed by several teams which could account for the demonstrated link between trauma and some PsA onsets. Both the greater familial risk for PsA than for RA or psoriasis alone and the excessive paternal transmission of PsA strongly suggest a genetic background, although so far only MICA-A9 (expressed on gut epithelial cells) seems to be associated with susceptibility to PsA independently from psoriasis. To make further genetics studies informative, a careful selection of unequivocal cases of PsA is needed, which requires criteria selecting patients at the "top of the mountain" of PsA. One can expect that the sets of criteria proposed by McGonagle or Fournié could satisfy this wish.