[How to diagnose and treat psoriasis of the nails]

Psoriasis is an inherited chronic hyper proliferative autoimmune disease. Nail involvement is common and is found in 61% of cases of cutaneous psoriasis, with lifetime incidence of 90%; 80 to 90% in patients with psoriatic arthritis. Classical manifestations on the nail apparatus are correlated with the origin site of the disease. The proximal matrix produces pitting, trachyonychia and Beau's lines, transverse grooves. The distal matrix (lunula) may appear spotted or erythematous in color. Inflammation of the mid or distal matrix causes leuconychia due to nail incorporation of parakeratotic cells. Nail bed and hyponychium can show onycholysis, oil drops (salmon patches) subungual hyperkeratosis and at the distal nail bed splinter hemorrhages. Induction or severe exacerbation of psoriasis may be due to drugs, such as β-blockers, lithium, antimalarial agents, anti-TNF and interferon.