CARP of Gougerot and Carteaud is a rare dermatosis seen usually in adolescents. It clinically manifests as persistent brown, scaly macules, papules, patches, or plaques. These lesions tend to be confluent at the center and become reticulated toward the periphery and are commonly located on the neck, interscapular, and intermammary regions and the axillae [4]. The etiopathogenesis of CARP is obscure till date, but data from few studies have hypothesized defective epidermal hyperkeratinization and an inherent tendency toward a hyperproliferative response to colonization by M furfur [5]. Recently, the presence of Dietzia spp in the skin has been proposed as an etiological factor in CARP. Other possible causes of CARP include endocrine abnormalities such as insulin resistance and hypothyroidism, a reaction to UV light, a variant of cutaneous amyloidosis, and genetic predisposition [1]. The histopathological characteristics of CARP include undulating basket-weave hyperkeratosis, focal acanthosis limited to the areas of elongated rete ridges, papillomatosis, and increased basal melanin pigmentation [6]. Occasionally, a mild perivascular lymphocytic infiltrate can be seen in the papillary dermis [5]. CARP is often clinically mistaken for pityriasis versicolor and usually shows no response to therapy with antifungal agents [7]. It was previously considered a clinical form of AN, but AN differs in location (axillae and neck in AN) and has a darker appearance than CARP [3,8]. Pseudoatrophoderma colli is a rare entity and is usually considered a variant of CARP. It clinically presents as atrophic and wrinkled lesions predominantly over the trunk and neck (thus named “colli”) [3].

The diagnostic criteria for CARP, as proposed by Davis et al [7] and Srinivas [9], require the following: (1) clinical presentation of scaly brown reticulated and papillomatous macules and patches; (2) the upper trunk and neck as the site; (3) negative potassium hydroxide staining of scales for spores and hyphae; (4) no response to antifungal agents; and (5) an excellent response to minocycline. 

Jo et al [10] proposed a change to the original criteria, which are as follows: (1) clinical presentation of scaly brown macules and patches, some reticulated and papillomatous; (2) the upper trunk, neck, or flexures as the site; (3) negative potassium hydroxide staining or lack of response to antifungal treatment; and (4) an excellent response to antibiotic treatment.

The main differentiating features of CARP, AN, and pseudoatrophoderma colli are summarized in Table 1 [3].

A variety of treatments for CARP are available, among which oral minocycline (50-100 mg twice daily) is the treatment of choice. Recently, azithromycin (250-500 mg thrice per week) has been used, given its better safety profile than that of minocycline. Other less effective oral treatments options for CARP include isotretinoin, acitretin, and etretinate. Various topical agents have also been used, including selenium sulfide, ketoconazole cream, tacalcitol, tazarotene, tretinoin, and calcipotriene (calcipotriol) [1].

CARP is a rare dermatosis with a chronic and recurrent course, predominantly afflicting adolescents. Its etiology is controversial, but it is widely considered a disorder of keratinization. Its morphology resembles that of various other dermatological conditions such as AN and pityriasis versicolor, and, as a result, it is frequently misdiagnosed and mistreated, leading to social embarrassment for the patient. Therefore, it is prudent for dermatologists to carry out comprehensive clinical and histopathological assessments to facilitate prompt diagnosis and management of this condition. There is no standard therapy for CARP, but various therapeutic options are available such topical and systemic retinoids, oral antibiotics, topical antifungals, urea, calcipotriol, etc. Minocycline remains the first-line treatment for this condition as patients respond well to it and have minimal side effects.