Pathogenetic and clinical rationale for TNF-blocking therapy in psoriatic arthritis

The classical definition of psoriatic arthritis (PsA) as an inflammatory arthritis associated with psoriasis reflects only in part the large spectrum of musculoskeletal disorders found in patients with psoriasis. In particular, enthesopathy, dactilytis, osteitis and axial involvement are frequently neglected and probably account for the unsatisfactory response of PsA to traditional drugs, such as NSAIDs, steroids and DMARDs. Furthermore, these drugs showed only a partial ability to influence radiographic progression and psoriasis. The new anti-TNF agents, in particular etanercept but also infliximab and adalimumab, have demonstrated a comprehensive effectiveness on the multiple aspects of the PsA disease, including quality of life and slowing of radiographic progression. Despite this clear efficacy, the actual mechanisms by which TNF-blocking agents are able to obtain all these effects are still incompletely understood. However, the success of this therapy suggested one of the best ways for further research in the field of PsA. In this new fashion, the most stimulating hypotheses involving TNF are those regarding genetic predisposition, angiogenesis and osteoclastogenesis.