Answer: B

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Confluent and reticulated papillomatosis (CRP) was first described in 1927 by Gougerot and Carteaud.10 It is a largely asymptomatic skin condition that manifests as multiple brown, hyperpigmented papules that can coalesce to form plaques.11 These papules and plaques exhibit epidermal changes, hyperkeratosis, and atrophy.11 The plaques may be pruritic in some individuals, but overall CRP is limited to the skin with no systemic involvement.11 CRP most commonly involves the upper trunk, axilla, and neck.

CRP can occur in any patient, but it has a higher predominance in white and adolescent individuals with a slight predilection for males over females.12 Proposed risk factors for CRP include some endocrinopathies, particularly obesity and diabetes. Careful evaluation must occur in these patients, especially those with diabetes, as CRP may be confused for insulin resistance-associated acanthosis nigricans.13 Exposure to ultraviolet light, as well as a diagnosis of amyloidosis have also been proposed as being associated with the diagnosis of CRP; however, neither of these associations has been validated in the literature.14,15 Although many associated conditions have been proposed,  the majority of patients diagnosed with CRP are healthy and lack any comorbid conditions.11

The pathogenesis of CRP involves disordered keratinization. Histologically, this can be identified by the presence of undulating basket-weave hyperkeratosis, papillomatosis, and focal acanthosis.11 Evaluation of the lesions by electron microscopy is also consistent with altered keratinocyte differentiation, showing disrupted cellular architecture and proliferation of lamellar granules (Odland bodies).11 Ultrastructure studies have also shown increased melanosomes within the hyperkeratotic stratum corneum.11  The etiology of these pathogenic skin changes resulting in CRP was originally thought to be due to an abnormal response to infection by the fungus Malassezia furfur. However, case reports have not consistently detected this species within the lesions in patients diagnosed with CRP. Additionally, antifungal therapy has been unsuccessful in treating the lesions associated with CRP. Currently, the most convincing etiology of CRP is now thought to be bacterial. In 2005, a novel actinomycete resembling Rhodococcus was identified in a patient with CRP, and more recently Dietzia papillomatosis was identified using a polyphasic taxonomic approach. 16,17 The latter species is now the main infectious cause implicated in CRP development. 16,17

The differential diagnosis for CRP includes other hyperpigmented, hyperkeratotic skin disorders such as terra firma-forme dermatosis, acanthosis nigricans, Dowling-Degos disease, Galli-Galli disease, and dyskeratosis congenita.11 CRP can be differentiated from TFFD through the use of 70% alcohol, which in this case would not remove the plaque.11 Acanthosis nigricans affects body-fold regions and is diagnosed clinically with a history of insulin resistance. Dowling-Degos and Galli-Galli are both autosomal-dominant genetic disorders resulting in progressive hyperkeratosis. Dyskeratosis congenita is a rare x-linked recessive disorder characterized by systemic abnormalities including dystrophic nails, oral mucosa leukoplakia, and overall shortened lifespans. Identification of the unique features of these diseases with similar presentations can assist in elucidating one from the other.

The diagnosis of CRP is made clinically, with histopathologic assessment used as an important tool to exclude other diseases. Shave biopsies will reveal many of the pathogenic features of CRP including hyperkeratosis, papillomatosis, focal acanthosis, and increased basal melanin pigmentation. Dermoscopic features include brownish pigmentation with overlying white scales.18 The location of the lesions, most commonly on the upper trunk and neck, can also be used as a tool for diagnosis. Additionally, negative fungal cultures, resistance to antifungal treatment, or a positive response to minocycline treatment all support the diagnosis of CRP.12

Treatment for CRP primarily consists of oral antibiotics. The first-line regimen includes minocycline 50 mg taken orally twice a day for 6 weeks.19 An alternative antibiotic regimen that may be used is azithromycin 500 mg orally once daily for 1 week or 500 mg 3 times a week for 3 weeks.11 Both of these antibiotic schedules have been shown to result in complete clearance of the lesions with no recurrence for up to 6 months after completing treatment.20 In addition to antibiotic therapy, topical retinoids may be used. These agents reduce keratinocyte proliferation and are most appropriate when the lesions are limited to areas of the body that the patient can easily reach in order to apply the retinoid. Lastly, systemic retinoids may be used in recalcitrant cases. However, given the relatively safe profile of minocycline and azithromycin, systemic retinoids are reserved for patients who do not respond to these oral antibiotics.11,12

Overall, CRP is an uncommon but treatable keratinizing disorder that primarily affects adolescents. It presents as hyperpigmented papules and plaques most commonly located in the axilla and on the trunk. The diagnosis is predominantly clinical; once diagnosed, treatment with oral antibiotics often results in complete resolution of the lesions.

In the case presented here, the histologic findings and lack of response to antifungal treatment were consistent with CRP. The patient was prescribed oral minocycline and the lesions began to fade, with complete resolution achieved in 6 weeks.

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Jay Patel, BS, is a medical student; Joan Fernandez, BS, is a medical student; and Christopher Rizk, MD, is a dermatology resident at Baylor College of Medicine, in Houston, Texas.


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