Confluent and reticulated papillomatosis (CARP) is a dermatosis presented by papillomatous papules and hyperpigmented scaly macules coalescing into centrally confluent plaques with a reticular peripheral pattern. It is an uncommon condition and mostly occurs on the trunk.
Confluent and reticulated papillomatosis (CARP), also known as Gougerot-Carteaud syndrome is a rare disorder first described by Gougerot and Carteaud in 1927 . It occurs in all age groups, races, and genders. Usually, patients are asymptomatic. However, they may experience mild pruritus. The lesions are most commonly observed on the trunk . Physical findings are limited to the skin.
CARP lesions begin as papules of 1 to 2 millimeters in diameters that are slightly hyperkeratotic to warty. They enlarge to form 4 to 5 millimeters lesions which coalesce and form confluent plaques centrally with a reticulated periphery. Skin markings are preserved, or in the neck and axillae, they may be exaggerated. It has been described as keratotic and vertically rippled plaques, and punctate pigmented papillomatosis  . Rarely, atrophic macules may also be seen. A fine powdery scale is produced upon scraping of the lesions. Dermoscopy reveals an ill-defined brownish pigmentation, covered with white scales and a pattern labeled "sulci and gyri" . The color of lesions in CARP are characterized by an early erythematous appearance that later evolves into a grayish brown color .
CARP lesions initially develop in the skin of epigastric or intermammary region, and over a period of weeks to months spread over the lower abdomen, breast, pubic area, and the flanks. Exceptions to this can occur, as in one case the lesions were confined to the cheeks and in another, they were confined to the pubic area  . The mucous membranes are spared but the involvement of the face, proximal extremities, and forehead may be seen  .
The diagnostic criteria for CARP is proposed as:
On potassium hydroxide (KOH) test, pityrosporum ovale or pityrosporum orbiculare spores and rarely hyphae may be found. A fungal culture may also reveal these microorganisms in some cases. On wood lamp examination, yellow fluorescence can occur if pityrosporum organisms are present. Electron microscopy can help detect alterations in the structure and arrangement of cornified cells in some lesions. An increase may be observed in transitional cell layer, the number of melanosomes in the stratum corneum, and the number of lamellar bodies in the stratum granulosum . On immunohistochemical analysis, suprabasal keratin 16 expression and an intense focal staining in the stratum granulosum are revealed, with an increased number of epidermal cells with Ki-67 binding in the stratum malpighii.
Histopathological features of CARP include: