A patient with 40% nail involvement shows pitting, oil-drop (salmon patch) discolouration, onycholysis, and subungual hyperkeratosis of all fingernails. He has plaque psoriasis. The nail finding most specifically associated with psoriatic arthritis (rather than psoriasis alone) is:

• A Pitting (geometric pitting)
• B Onycholysis
• C Subungual hyperkeratosis
• D Oil-drop sign (salmon patch) ✓

Explanation

Among nail psoriasis features, the oil-drop (salmon patch) sign — a yellowish-orange discolouration under the nail plate — most strongly correlates with psoriatic arthritis (PsA) in multiple studies. It represents psoriatic involvement of the nail bed (hyponychium area) close to the DIP joint, which is enthesally linked to the nail apparatus. Pitting (geometric, regular pits) reflects matrix disease and is the most common nail change in psoriasis overall. Onycholysis is more strongly associated with nail bed involvement but has less specific correlation with PsA compared to oil-drop.

Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.