Nail involvement as a negative prognostic factor in biological therapy for psoriasis: a retrospective study.

Psoriatic arthritis (PsA) is an immunologically mediated seronegative arthritis, part of psoriatic disease. The proportion of psoriatic patients developing PsA ranges from 6 to 42%1,2 affecting up to 1% of the global population. The severity and the clinical appearance of the PsA is markedly variable, ranging from mild mono-/oligo-arthritis to severe erosive and destructive articular diseases. Even though the articular manifestations may precede the cutaneous manifestations (i.e. <15% of cases) , PsA has been reported to appear on average 10 years after the onset of cutaneous psoriasis. Therefore, the dermatologist plays an important role in identifying PsA at early stage, before the joint damage becomes irreversible.