What further history, physical exam, or laboratory tests should be completed (hypothesis testing)?
FIGURE 1 This patient’s fingernail had been discolored for months and the fingertip had recently begun to hurt. FIGURE 2 A brown discoloration (oil spot) in the patient’s proximal nail. Pattern recognition Figure 1 shows a brownish discoloration of the fingernail, with small pits particularly prominent around the lunula (the semicircular light area adjacent to the proximal nail fold). There is also evidence of onycholysis (separation of the nail from the nail bed). The vertical ridging is not abnormal. Figure 2 shows a well-circumscribed brown discoloration in the proximal nail called an oil spot. These nail findings are classic for psoriasis.1 Figure 1 also shows subtle swelling of the distal interphalangeal (DIP) joint. It is this area the patient said was painful, and she had joint tenderness to palpation over this DIP joint only. Hypotheses The 2 most likely diagnoses are: psoriasis causing nail changes while psoriatic arthritis is developing onychomycosis with incidental joint pai
