The FP noticed a lacy net-like or reticulate appearance and thin brown papules to warty plaques over the trunk and recognized this condition as confluent and reticulated papillomatosis (CARP). A potassium hydroxide (KOH) test of a skin scraping failed to reveal yeast forms or hyphae. The FP determined that a biopsy was not necessary for diagnosis due to the distinct clinical appearance and negative KOH test. However, a biopsy could have distinguished this presentation from similar appearing disorders, including acanthosis nigricans and pityriasis versicolor.
CARP is an uncommon disorder of keratinization that affects adolescents and young adults, and is more common in Caucasians. A classic presentation involves the neck, chest, and abdomen. The differential diagnosis includes acanthosis nigricans and pityriasis versicolor, as well as more rare disorders that include Darier disease and keratosis follicularis.
There appears to be an association between the disorder and weight (specifically, being overweight). In addition, some familial cases have been reported.
Most recently, Dietzia papillomatosis, a gram-positive actinomycete has been implicated as a likely cause, which supports antibiotic therapy as the first-line approach. Minocycline 50 mg bid for 6 weeks clears the papules and plaques for most patients. Azithromycin and clarithromycin are alternatives, with various dosing strategies lasting 6 to 12 weeks. Complete clearance may take months to more than a year. About 15% of patients will experience recurrence.
This patient was treated with minocycline 50 mg bid for 12 weeks, a more common strategy at the time she was diagnosed. This led to complete clearance at 3 months, and she remained clear a year after beginning treatment.
Photos and text for Photo Rounds Friday courtesy of Jonathan Karnes, MD (copyright retained).