1. About a year ago, this 40-year-old man developed scaling on the distal one-third of his thumbnail. The condition began to worsen, leaving most of his thumb covered by thick adherent white scales on a pinkish base with sharply defined margins. The adjacent thumbnail has focal areas of pitting in the nail plate, as well as yellowish discoloration on the distal edge.
Diagnosis: The most likely diagnosis is psoriasis, which can manifest with localized involvement.
For more information, see “Thumb: Scaling with Pitted Nail Plate.” Clin Rev. 2013 March;23(3):11.