Answer: D

Confluent and reticulated papillomatosis (CARP) is an epidermal dermatosis resulting
from disordered keratinization.10,11 Also referred to as Gougerot-Carteaud syndrome, CARP was first reported in 1927; an American case was not reported until 1937.10-12 Although initially thought to be a form of acanthosis nigricans, CARP was later recategorized as a distinct dermatosis.10

CARP has been reported in patients ranging from 5 to 63 years of age, but the most common age of onset is during puberty.13 Studies in Japan and the United States have reported similar ages of onset (17 and 15 years of age, respectively).10,13,14 Reports in the literature conflict about the male to female ratio, with some citing a greater frequency in men10,14,15 and others reporting the opposite.13 Cases of CARP have been reported worldwide.10,11,15

Theories on the etiology of CARP have evolved over time. Initially CARP was thought to be caused by an abnormal host response to Malassezia furfur,10,11,13 whereas current theories propose that CARP is caused by the gram-positive anaerobic bacteria Dietzia papillomatosis.10,11,13,16 Other potential noninfectious causes include ultraviolet light, overexpression of keratin-16, and amyloidosis.10,11

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The histology of CARP demonstrates focal acanthosis, hyperkeratosis, and papillomatosis. CARP displays increased lamellar granules in the stratum granulosum and increased melanosomes in the stratum corneum.13 Coupled with its response to treatment with vitamin A and D derivatives, these findings suggest that CARP is a disorder of impaired keratinization.11,13

Risk factors for CARP include obesity and diabetes, which cause hyperinsulinemia leading to increased activation of insulin-like growth factor, epidermal growth factor, fibroblast growth factor, and tyrosine kinase receptors. This, ultimately, results in epidermal proliferation, mitogenesis, and inhibited apoptosis.10,11 CARP has been found to arise more frequently in women with polycystic ovarian syndrome and may be accompanied by acanthosis nigricans in such instances.17

Clinically, CARP rarely is symptomatic, although some patients experience pruritus. The disease is limited to the skin, with no systemic findings. It is found most commonly on the upper trunk, axillae, and inframammary regions.10,13 It presents as velvety, hyperpigmented, verrucous papules that reticulate on the periphery and coalesce as plaques in the center.10,11,14 CARP also can form a distinct rhomboidal pattern posteriorly in the interscapular region or anteriorly on the chest.10,13 In White individuals, the macules or papules can be erythematous or scaly and also can appear dry and mottled.10,11,13,14 The velvety look of CARP can appear similar to acanthosis nigricans.13

Diagnostic criteria for CARP, established by Davis et al14 and revised by Jo et al,18 are as follows: scaly brown patches and macules that include reticulated or papillomatous lesions, negative fungal staining, lack of response to antifungal therapy, excellent response to minocycline or antibiotic therapy, and involvement of the upper trunk and neck.11 Dermoscopy may aid in diagnosis, revealing sulci and gyri folds, brown pigmentation, and white scale.10,19

The differential diagnosis of CARP includes acanthosis nigricans, which can be differentiated from CARP histologically or by the clinical absence of peripheral reticulation. The 2 diseases can also occur concomitantly in the same individual.10 Other conditions in the differential diagnosis include tinea versicolor, Galli-Galli disease, Dowling-Degos disease, dyskeratosis congenita, prurigo pigmentosa, and terra firma–forme dermatosis (Table).10,11,19 Prurigo pigmentosa may be differentiated by a skin biopsy and terra firma–forme dermatosis by a swab test with 70% isopropyl alcohol.10

Treatments for CARP include antibiotics and topical (tazarotene) and systemic retinoids.10,11 Minocycline is the first-line antibiotic therapy11; tetracycline and doxycycline also have shown effectiveness.10 The recommended dosage of minocycline is 50 mg twice daily for 6 weeks.11,13 For individuals unable to take minocycline due to pregnancy, azithromycin is first-line treatment.10,11 Clarithromycin and erythromycin also have been described as effective treatment options.10,11,13

Other topical therapies include calcipotriol, tacrolimus, and urea.10,13 When patients do not respond to minocycline, systemic isotretinoin may be considered.10 Patients generally have a good response to therapy, with greater than 50% improvement in those treated with minocycline or azithromycin. Recurrences tend to occur in patients who were not treated with antibiotic therapy.10

The patient in this case was diagnosed with CARP clinically and was prescribed 6 weeks of minocycline, which led to regression of his lesions.

Dina Zamil, BS, is a medical student at Baylor College of Medicine, Tara L. Braun, MD, is a resident in the Department of Dermatology at Baylor College of Medicine, and Christopher Rizk, MD, is a dermatologist affiliated with Baylor College of Medicine, in Houston, Texas.


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