What clue in the photo points to the cause of this chronic hand dermatitis?

Case 1:
A 46-year-old dentist presents for evaluation of chronic hand dermatitis of 1 year’s duration. He has no other rashes. Standard patch testing was negative. Another physician prescribed a high-potency corticosteroid cream that controls the rash but does not clear it. The patient takes no other medications.

What are you looking at here?

A. Contact dermatitis.
B. Psoriasis.
C. Lichen planus.
D. Dermatophyte infection. E. Atopic dermatitis.

Bonus question: What clue in one of the photos shown here can assist you in making the diagnosis?

Answer to bonus question: The presence of nail pitting pointed to the diagnosis of psoriasis, B.

Further history revealed that the patient had been undergoing a divorce. In addition to the stress resulting from the divorce, his hand washing and trauma from his work as a dentist contributed to the psoriasis. Contact dermatitis is a possibility, and patch testing is often required to rule it out. Lichen planus usually presents with purple polygonal papules that are unlike the rash seen here. Atopic hand dermatitis can appear later in life with diminishing production of skin oils and excessive exposure to soap and water. Dermatophyte infections can present with scaling on the palms; a potassium hydroxide examination or fungal culture is required if such an infection is suspected.