Confluent and reticulated papillomatosis of Gougerot and Carteaud, also known as Gougerot-Carteaud syndrome, is an uncommon skin disorder of young individuals characterized by hyperkeratotic or verrucous brown papules or plaques that coalesce centrally and by a reticulated pattern peripherally. It was first described by two French dermatologists, Gougerot and Carteaud, in 1927.1 Initially, the distinct entity of CARP was contested, with some dermatologists believing it to be a variant of acanthosis nigricans. However, CARP is now recognized as a distinct, though rare, dermatosis.
Histopathology reveals findings similar to those that may be found in acanthosis nigricans and epidermal nevi. Classic characteristics of CARP include hyperkeratosis, papillomatosis, increased basal melanin pigmentation, and mild acanthosis. Occasionally, there may be perivascular lymphocytic infiltrates in the superficial dermis.3,4
The etiology of CARP is unknown. CARP’s resolution in response to antibiotics and the isolation of two bacterial actinomycetes, Rhodococcus and Dietzia papillomatosis, from skin scrapings of CARP patients have led some to believe that its etiology is bacterial. However, no bacterial species have been consistently isolated from CARP patients. The prevailing theory of the past was that CARP was an abnormal host response to the fungus Malassezia furfur. Inconsistent detection of the fungus in skin scrapings, as well as persistence of the skin lesions after fungal clearance with antifungal therapy, has debunked this theory. An underlying disorder of keratinization resulting in hyperproliferation also has been suggested given reports of familial CARP and electron microscopy studies demonstrating focal-enhanced expression of keratin-16 in the stratum granulosom.5 Other theories include a cutaneous response to underlying endocrinopathies, ultraviolet light, and localized amyloidosis.1
Diagnosis and differential
CARP is poorly recognized by clinicians and frequently initially misdiagnosed due to its similar appearance to other disorders, most commonly tinea versicolor and acanthosis nigricans. Davis et al. proposed criteria for diagnosis of CARP requiring 1) presence of scaly, reticulated and papillomatous brown macules and patches; 2) distribution over the upper trunk and neck; 3) negative fungal staining of scales; 4) no improvement following antifungal treatment; and 5) improvement following minocycline.2
Tinea versicolor may appear similar to CARP, but unlike CARP, will respond to antifungal treatment and may demonstrate hyphae and yeast on KOH preparation. Acanthosis nigricans and CARP both may present with velvety, hyperpigmented plaques in individuals of obese habitus or with insulin resistance, but peripheral reticulation will be absent in acanthosis nigricans. However, acanthosis nigricans and CARP may coexist, and this coexistence is not uncommonly seen in individuals with obesity and/or insulin resistance. Darier’s disease may look similar to cases of CARP without pigmentary change, but it often will have accompanying nail changes. Macular or lichen amyloidosis may present with pruritic brown macules or papules, but skin biopsy will have positive amyloid staining. The use of 70% alcohol swabbing to diagnose terra firma-forme dermatosis, with lesions disappearing with swabbing, is classic and used to differentiate it from CARP. Other conditions to consider include seborrheic dermatitis, epidermal nevi, verruca plana, epidermodysplasia verruciformis, and acne vulgaris.1,2,4
Minocycline is the first-line treatment for CARP: 80% of patients may have complete resolution with minocycline, while the remainder experience at least 50% clearance of skin lesions.2 However, recurrence after stopping minocycline treatment is not uncommon. The mechanism by which minocycline works is unknown. Second-line treatment for those who cannot tolerate minocycline are macrolide antibiotics.6 Other treatment options with reported success include oral isotretinoin and topical retinoids, including tretinoin gel and tazarotene cream.3,7 Appropriate strength topical corticosteroids may be used for pruritus.
Ms. Han is a medical student at the University of California, San Diego. Dr. Eichenfield is chief of pediatric and adolescent dermatology at Rady Children’s Hospital–San Diego, as well as the vice chair of the department of dermatology and a professor of dermatology and pediatrics at UC San Diego. They report having no conflicts of interest or financial disclosures. Email them at.