What is This Rash?

Case Report

A 16-year-old adolescent boy presented with a 2-year history of an expanding, dark eruption involving the chest, abdomen, axilla, and upper extremities. There was no pruritus or other associated symptom. Physical examination revealed hyperpigmented patches with minimal overlying scale in a confluent pattern on the lower chest and upper abdomen (Figure 1). A symmetrical, reticulated pattern of similar hyperpigmented patches was appreciated on the outer pectoral regions, axilla (Figure 2), and upper extremities.

What is the Diagnosis?

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Diagnosis: Confluent and reticulated papillomatosis (CARP) 

CARP was originally described by Gougerot and Carteaud (hence, Gourgerot-Carteaud syndrome) in 1927.¹ CARP presents with hyperkeratotic or verrucous papules and hyperpigmented macules with overlying scale, which coalesce into patches or plaques on the central body (Figure 1) and a reticular pattern peripherally (Figure 2).¹ Lesions frequently progress from an erythematous to a dull brown color and initially target the inframammary or epigastric regions, spreading to involve the chest, neck, and axilla.¹ Neck and axilla involvement are associated with an accentuation of morphology, which may be useful in clinical diagnosis. CARP is primarily asymptomatic, although pruritus has been reported in up to 20% of patients.²

Etiology and Differential Diagnosis 
Among the potential etiologies for CARP, the most accepted theory relates to abnormal keratinocyte differentiation and maturation, evident by alteration of cornified cell structures, increased lamellar granules in the stratum granulosum, increased melanosomes in the horny layers, and insignificant changes to epidermal melanocytes.^1,3,4 These findings are supported by treatment responses to retinoids and vitamin D derivatives.⁴ CARP is frequently misdiagnosed as tinea versicolor, demonstrated in our patient’s presentation. Numerous theories exist describing the abnormal keratinization in CARP being a result of an inflammatory response to Malassezia, yet cultures for Malassezia or additional proposed organisms (Rhodococcus, Dietziaceae) have not been consistently positive.¹ As a result, a lack of fungal isolation and failed improvement with antifungal treatment are proposed diagnostic criteria.² CARP may also be misdiagnosed as acanthosis nigricans as a result of numerous shared clinical and histologic features, and a possible link between the two conditions has been proposed. However, the majority of patients with CARP lack endocrinopathies, obesity, or visceral malignancy and improve with minocycline or retinoid therapy.^1,2

Histology
Occasionally, the utilization of skin biopsy may be necessary to diagnosis CARP. Histologic findings seen in CARP include papillomatosis, hyperkeratosis, and a superficial perivascular infiltrate.^1,5 However, histologic findings mimic similarly presenting diagnoses, such as acanthosis nigricans. To differentiate between acanthosis nigricans and CARP, the presence of microscopic follicular plugging can be assessed and favors the latter.⁵   

Management
CARP usually persists if left untreated, with a mean duration of 3 years.² Minocycline is considered a first-line therapy as a result of its extensive reporting for CARP treatment.² Minocycline’s anti-inflammatory properties are proposed to be the reason behind its efficacy, while its antibacterial properties are suspected to be less important as bacteria have failed to be consistently isolated.² Topical retinoids and vitamin D analogs have been less studied, despite theories of abnormal keratinization resulting in CARP. Recurrence after cessation of treatment may occur, necessitating an extended treatment regimen.

Our Patient 
Past medical history ruled out diabetes, hypertension, obesity, and a family history of a similar eruption. The patient had previously been treated without improvement using oral fluconazole after a diagnosis of tinea versicolor had been made. Based on the clinical findings and previous failed treatment regimen, a diagnosis of CARP was made. The patient was treated with minocycline 50 mg, twice daily, for 45 days.

Conclusion
CARP is an uncommon dermatosis mimicking a myriad of cutaneous eruptions, including tinea versicolor and acanthosis nigricans. The diagnosis of CARP is often made clinically, but a negative KOH examination may assist in ruling out similarly presenting fungal infections. Minocycline is a well-studied, effective therapy in the treatment of CARP. n 

Mr Visconti is a fourth-year medical student at Michigan State University College of Osteopathic Medicine in Grand Rapids, MI. Mr Bashyam is a research fellow at the Center for Dermatology Research at Wake Forest University School of Medicine in Winston-Salem, NC. Dr Feldman is with the Center for Dermatology Research and the departments of dermatology, pathology, and social sciences & health policy at Wake Forest University School of Medicine and the department of dermatology at the University of Southern Denmark, Odense, Denmark.

Disclosures: Mr Visconti and Mr Bashyam report no relevant financial relationships. Dr Feldman has received research, speaking and/or consulting support from a variety of companies including Galderma, GSK/Stiefel, Almirall, Leo Pharma, Boehringer Ingelheim, Mylan, Celgene, Pfizer, Valeant, AbbVie, Samsung, Janssen, Lilly, Menlo, Merck, Novartis, Regeneron, Sanofi, Novan, Qurient, National Biological Corporation, Caremark, Advance Medical, Sun Pharma, Suncare Research, Informa, UpToDate, and National Psoriasis Foundation.  He is founder and majority owner of www.DrScore.com and founder and part owner of Causa Research, a company dedicated to enhancing patients’ adherence to treatment.  

References
1. Scheinfeld N. Confluent and reticulated papillomatosis: a review of the literature. Am J Clin Dermatol. 2006;7(5):305-313. doi:10.2165/00128071-200607050-00004

2. Davis MDP, Weenig RH, Camilleri MJ. Confluent and reticulate papillomatosis (Gougerot-Carteaud syndrome): a minocycline-responsive dermatosis without evidence for yeast in pathogenesis. A study of 39 patients and a proposal of diagnostic criteria. Br J Dermatol. 2006;154(2):287-293. doi:10.1111/j.1365-2133.2005.06955.x

3. Jimbow M, Talpash O, Jimbow K. Confluent and reticulated papillomatosis: clinical, light and electron microscopic studies. Int J Dermatol. 1992;31(7):480-483. doi:10.1111/j.1365-4362.1992.tb02694.x

4. Bowman PH, Davis LS. Confluent and reticulated papillomatosis: response to tazarotene. J Am Acad Dermatol. 2003;48(5 suppl):S80-S81. doi:10.1067/mjd.2003.155

5. Tamraz H, Raffoul M, Kurban M, Kibbi AG, Abbas O. Confluent and reticulated papillomatosis: clinical and histopathological study of 10 cases from Lebanon. J Eur Acad Dermatol Venereol. 2013;27(1):e119-123. doi:10.1111/j.1468-3083.2011.04328.x