Enliven: Clinical Dermatology

Dermatosis papulosa nigra is a common, benign skin condition characterized by multiple, asymptomatic, superficial, black or dark-brown, round, domeshaped or flat, macules or more often papules. The size of individual lesion usually ranges from 1 to 5 mm. Sites of predilection include the face, neck, and upper trunk. Dermatosis papulosa nigra occurs predominantly in darker-skinned individual. The incidence increases with age and is rare before puberty. The male to female ratio is approximately 1:2. There is a genetic predisposition. Ultraviolet irradiation may have a role to play. Activating point mutations of the FGFR3 and the PIK3CA genes are involved in the pathogenesis. Treatment is usually not necessary apart from reassurance about the benign nature of the condition. For those patients in whom treatment is desired mainly for esthetic reasons, treatment options most commonly include: curettage, ablative laser, excision, and electrofulguration. Liquid nitrogen cryotherapy can also be tried in some cases with great care due to higher risk of side effects.

Keywords

Hyperpigmentation; Papules; Dark-skin; Mutations; FGFR3; PIK3CA; Benign; Reassurance

Introduction

Dermatosis papulosa nigra is a common, benign skin condition characterized by multiple, asymptomatic, pigmented, round, dome-shaped or flat, papules or macules localized predominately on the face, neck, and upper trunk [1,2]. The condition was first described by Aldo Castellani in 1925, based on his observations made while visiting Central America and Jamaica [3].

Epidemiology

Dermatosis papulosa nigra occurs predominantly in dark-skinned individual (Fitzpatrick skin phototypes IV to VI) [2]. The incidence in adult blacks is between 10 and 30% [2]. Asian patients are also prone to these lesions. The condition is rare in Caucasians [4]. The incidence increases with age and is rare before puberty [4,5]. The peak incidence is in the sixth decade [4,5]. The male to female ratio is approximately 1:2 [4,6].

Etiopathology

The exact etiology is not known. It is believed that the condition is caused by a defect in the nevoid development of the pilosebaceous follicle [4]. There is a genetic predisposition as there is a positive family history in approximately 50% of affected individuals [1,4]. As the condition occurs mainly in the sun-exposed areas, ultraviolet irradiation may have a role to play. It has been shown that activating point mutations of the FGFR3 (fibroblast growth factor 3) and the PIK3CA (encoding for the catalytic p110 subunit of class 1 phosphatidylinositol 3-kinase) genes are involved in the pathogenesis of dermatosis papulosa nigra [7]. Some authors consider dermatosis papulosa nigra to be a variant of seborrheic keratosis in people with dark skin [7].

Histopathology

Histological examination of the lesion shows hyperkeratosis, papillomatosis, and acanthosis, invaginations of the epidermis with elongation of the rete ridges (horn cysts), and marked hyperpigmentation of the basal layer [8].

Clinical Manifestations

Clinically, dermatosis papulosa nigra presents as multiple, asymptomatic, superficial, black or dark-brown, round, dome-shaped or flat, macules or more often papules (Figure 1) [2]. In the early stage, the lesions are often smooth-surfaced. Later, they become roughened and at times verrucous. Some of the lesions may be filiform or pedunculated. The size of individual lesion usually ranges from 1 to 5 mm [9]. Sites of predilection include the face (predominantly the malar regions), neck, and upper trunk [2]. They do not tend to group or occur in a linear fashion. The lesions increase in size and number over time.

Figure 1. Dermatosis papulosa nigra presenting as multiple, smooth, dark-brown, round, dome-shaped papules in the malar area of a black woman.

Diagnosis