The FP conducted a physical exam and noticed bilateral dorsal foot dermatitis with occasional small vesicles and lichenified papules, which was suggestive of chronic contact or irritant dermatitis. The patient’s favorite pair of boots offered another clue as to the most likely contact allergens. (The boots were leather, and leather is treated with tanning agents and dyes.) A biopsy was not performed but would be expected to show spongiosis with some degree of lichenification (thickening of the dermis)—a sign of the acute on chronic nature of this process. The diagnosis of irritant or allergic contact dermatitis was made empirically.
The differential diagnosis for rashes on the feet can be broad and includes common tinea pedis, pitted keratolysis, stasis dermatitis, psoriasis, eczemas of various types, keratoderma, and contact dermatitis.
Many patients misconstrue that materials they use every day are exempt from becoming allergens. In counseling patients about this, point out that contact allergens often arise from repeated exposure. For example, dentists often develop dental amalgam allergies, hair professionals develop hair dye allergies, and machinists commonly develop cutting oil allergies. These reactions can and do occur years into their use.
The patient was started on topical clobetasol 0.05% ointment bid for 3 weeks, which provided quick relief and cleared his feet of the patches and plaques. He continued to wear his boots until contact allergy patch testing was performed in the office over a series of 3 days. This revealed an allergy to chromium, a common leather tanning agent. The patient was advised to avoid leather products including jackets, car upholstery, and gloves. After he carefully chose different footwear without a leather insole or tongue, the patient required no further therapy and remained clear.
Photos and text for Photo Rounds Friday courtesy of Jonathan Karnes, MD (copyright retained).