March 2007

This 18-year-old girl presented to the dermatologist with complaints of brown papules in a net-like pattern on her upper back, as well as in the inframammary area. The papules had evolved over several weeks. These were mostly of cosmetic concern to her as they were not painful or pruritic. She denied any illness preceding the eruption.

What is your diagnosis?

Answer

This young woman has confluent and reticulated papillomatosis (CARP).

Originally described by Gougerot and Carteaud in 1927, this disorder starts with 1 mm to 2 mm brown to tan papules arising most commonly in the inframammary area. During a few weeks, the papules enlarge and become more hyperkeratotic and show increased pigmentation. Centrally, the papules coalesce but remain reticulated at the periphery. Involvement of the neck, shoulders, back and upper abdomen may occur. The papules and plaques of CARP are most often asymptomatic; however, some occasionally show mild pruritus. This disorder occurs in all ages and sexes throughout the world, but is most common during puberty and is 2.5 times more common in women than men. Blacks are twice as likely to develop the disease than whites.

The etiology of CARP is not clear. A variety of bacteria and fungi have been implicated due to the clearance of the eruption after antibiotic therapy in many cases. Most recently, a previously unknown species of actinomyces was shown to be associated. In addition, the similarity in clinical and histological appearance of CARP and acanthosis nigricans, as well as the occasional association with a variety of endocrine disorders, has led others to believe CARP may be due to an endocrine imbalance. Finally, familial cases and the response to a variety of keratolytics have led others to believe this is a disorder of keratinization. To date, no clear cause for CARP has been shown. The myriad treatments that have been successful in clearing the eruption suggest that CARP may be due to a variety of causes. The differential diagnosis of CARP includes acanthosis nigricans and tinea versicolor.

A variety of treatments have been used successfully including oral antibiotics, topical selenium sulfide, oral and topical retinoids, topical calcipotriene, and a variety of topical keratolytics. Most authors recommend starting with a tetracycline in age appropriate individuals, although a variety of antibiotics have been used with clearance of the disease. Not uncommonly, the eruption will recur after cessation of treatment.

For more information:

• Scheinfeld N. Confluent and reticulated papillomatosis: a review of the literature. J Clin Dermatol. 2006;7:305-313.
• Jang HS, Oh CK, Cha JH, et al. Six cases of confluent and reticulated papillomatosis alleviated by various antibiotics. J Am Acad Dermatol. 2001;44:652-655.
• Pierson D, Bandel C, Ehrig T, Cockerell. Benign Epidermal Tumors and Proliferations. In: Bolognia J, Jorizzo JL, Rapini RP, eds. Dermatology. Philadelphia: Mosby; 2003:1717-1718.