LAUSR

A 35-year-old man presented with a 3-year history of pruritic rash. On presentation, he was taking dupilumab (Dupixent; Regeneron & Sanofi) 300 mg subcutaneously every 2 weeks for 1 year prescribed by a previous provider for presumed atopic dermatitis. The patient reported minimal improvement. Examination revealed a violaceous red plaque on the right lower flank with scattered pink red papules and excoriations on the trunk and extremities. Punch biopsy of the flank lesion revealed lichen simplex chronicus. At his initial visit, treatment with dupilumab was discontinued, and he was prescribed topical triamcinolone and tacrolimus ointments. At follow-up visit 6 weeks later, examination demonstrated a larger, bright red, welldemarcated, edematous plaque located over the right lower flank (Fig. 1) with excoriated clustered red papules on extremities. Repeat punch biopsies of the right flank and left forearm revealed subacute spongiotic dermatitis. Because of the persistent and localized nature of his eruption, patch testing was performed using the North American Contact Dermatitis Group standard of 70 allergens. After 48 hours, the patches were removed, and the patient was noted to have a 3+ reaction tomixed dialkyl thiourea and equivocal reactions to ammonium persulfate and p-tert-butylphenol formaldehyde resin. A second reading was performed at 96 hours and revealed a 3+ reaction to mixed dialkyl thiourea, 2+ reaction to ammonium persulfate and 1+ reaction to p-tert-butylphenol formaldehyde resin (Fig. 2). Further questioning revealed that the patient, who is a law enforcement officer, wore a gun holster lined with neoprene over his right flank (Fig. 3). He recalled a similar rash years prior on his right ankle at the site of a gun holster, which resolved after relocating the holster to the hip.