Psoriatic arthritis. When the heterogeneity requires normality.

Psoriatic arthritis (PsA) is characteristically associated with a large spectrum of disorders, some of which are peculiars, such as enthesopathy, dactilytis, osteitis and axial involvement. Due to the heterogeneity of its expression, definition and classification of PsA have been unsatisfactory until recent years, with consequences on the reliability of epidemiological studies. Other confounding factors for diagnosis and classification of PsA are the radiological changes, sometimes found in asymptomatic patients with psoriasis, and the frequent normality of acute phase response indices, in particular erythrocyte sedimentation rate and C reactive protein. All these aspects are frequently neglected and probably account also 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 anti-TNF agents have demonstrated to be able to influence all the multiple aspects of the PsA disease and indeed, to slow radiographic progression and to improve patients' quality of life. This seems obtained with a convenient cost-effectiveness ratio.