A 50-year-old man is sent to dermatology for evaluation of a “fungal infection” affecting both of his thumbnails. In the past several years, treatment with at least two courses of oral terbinafine and numerous topical antifungal creams has failed to produce any improvement in the problem. The patient denies any nail-related symptoms or trauma to his thumbs.
The patient claims to be otherwise healthy. On further questioning, however, he admits to having intermittent joint pain and swelling, especially in one ankle. He adds that for the past several years, he has experienced severe back pain and stiffness in the morning.
EXAMINATION
The patient looks his stated age, is in no acute distress, and is well developed and well nourished.
Both thumbnails demonstrate identical changes: separation of the distal one-third of the nail plate from the nail bed and yellowish discoloration of that portion of the nails. In and under the nail plate, fine, short, longitudinal black streaks are seen. Proximally, a well-defined brown band is observed in the subungual areas. The patient’s other nails are unaffected.
Broader examination reveals a salmon-pink rash with white scale covering the periumbilical area. A similar rash is seen in the upper intergluteal area.
What is the diagnosis?