INTRODUCTION

Confluent and reticulate papillomatosis (CARP), or Gougerot–Carteaud syndrome, is a rare keratinization disorder presenting in young adults with a slight male predilection. It usually causes asymptomatic, hyperpigmented papules on the upper chest and neck, which may eventually form plaques [1,2]. Although the exact etiology remains unknown, Malassezia furfur was once believed to be the causative agent, yet recent studies have shown that the gram-positive aerobic actinomycete Dietzia papillomatosis may be responsible [1,3]. Other hypothesized triggers include amyloidosis, diabetes, obesity, UV radiation exposure, and the overexpression of keratin-16. While there has been some success with topical keratolytics, retinoids, and antifungals, anti-inflammatory dosages of antibiotics such as minocycline have been the preferred therapeutic approach [1].

CASE REPORT

A 58-year-old male presented with itchy, dark lesions on the back and upper extremities persistent for the past ten years (Fig. 1). He reported severe pruritus, affecting his sleep and daily activities, and brought a zip-lock bag containing remnants of excoriated skin to evidence his discomfort. He had taken multiple oral and topical treatments for the same with minimal to no improvement, the details of which could not be procured. He admitted to having a history of blowing hot air using a blow-dyer over the lesions and scrubbing and manipulating the lesions with blunt objects to get temporary symptomatic relief. He was also a known case of uncontrolled diabetes mellitus with no other comorbidities. On examination, there were multiple confluent, lichenified papules and plaques distributed on the upper back and extensor aspect of the upper arms with minimal scaling. KOH was done and was found to be negative for fungal elements. A trial of oral itraconazole 200 mg once daily was given for one month with no improvement. Dermoscopy showed fine, white scales with a brown, cobble-stone pattern (Fig. 2) [4]. Histopathology revealed a hyperkeratotic epidermis with acanthosis and papillomatosis, basilar hypermelanosis, and a perivascular lymphocytic inflammatory infiltrate with dense collagen deposition in the dermis, which was suggestive of CARP. (Fig. 3) [5]. The patient was managed with 65 mg of extended-release (ER) oral minocycline once daily for one month, and the lesions resolved. Maintenance therapy included topical clobetasol propionate and oral antihistamines.

	Figure 1: Multiple hyperpigmented, scaly papules and plaques with central confluence and peripheral reticulated pattern on the nape of the neck and upper back (pretreatment).
	Figure 2: Fine, white scales with dark brown globules separated by whitish striae creating a cobblestone pattern.
	Figure 3: Basket-weave hyperkeratosis of the epidermis, increased basal melanin pigmentation, and perivascular lymphocytic inflammatory infiltrate with dense collagen deposition in the dermis (H&E; 100x).

DISCUSSION

CARP may mimic an array of various dermatoses such as acanthosis nigricans (AN), dermatophytosis, terra firma-forme dermatosis, and reticulated hyperpigmentation without papules or plaques, which may occur in Dowling–Degos disease, Galli–Galli disease, and dyskeratosis congenita [1]. Diagnosis is based primarily on clinical evidence, although histopathology is still a crucial tool for excluding other dermatoses. Davis et al. proposed the following diagnostic criteria for CARP: (1) clinical findings of scaly, brown macules and patches that appear reticulate and show signs of papillomatosis; (2) involvement of the upper trunk and neck; (3) negative fungal staining of scales; (4) no response to antifungal treatment; and (5) excellent response to minocycline treatment [6]. These conditions were satisfied in our case.

Although there is no standardized treatment plan for the management of CARP, various modalities have been tried due to its uncertain etiology. Minocycline’s anti-inflammatory properties, which restrict neutrophil migration, inhibit matrix metalloproteinases, and stop the generation of reactive oxygen species, are believed to be more important for its therapeutic effectiveness than its antibacterial effects.

Writers have described using 100–200 mg of minocycline daily for three weeks to three months. One report suggests changing to alternate-day therapy for five months because of the chances of recurrence. The administration of ER minocycline once daily reduces the risk of side effects of conventional therapy, including lupus, drug-induced hypersensitivity syndrome, ototoxicity, and pigment abnormalities, and improves patient compliance [7]. We achieved satisfactory results with ER minocycline tablets for one month, and although mild recurrence was present, it was managed conservatively with topical corticosteroids.

CONCLUSION

Due to the rare nature of the disease, CARP lacks standard treatment guidelines. Hence, further studies are warranted to confirm the therapeutic efficacy of ER minocycline as it represents a convenient treatment option due to the once-daily dosing regimen and the favorable side effect profile.