Dermatoscopy of Urticaria Pigmentosa with and without Darier's Sign in Skin of Colour

Abstract

Urticaria pigmentosa is the most common form of mastocytosis that often develops in infancy or early childhood. We report two male children– first, a 7-month-old child with a history of asymptomatic multiple dark colored skin lesions macules with wheals on gentle rubbing (Darier's sign) and second, a 2-year-old child with similar clinical presentation without Darier's sign. Dermoscopy showed dark brown lines in a reticulate pattern which is an exaggeration of the pigment network seen in the normal skin. The reticulate pigment network was darker and thicker in the child with positive Darier's sign. This is the first case report of dermoscopy of urticarial pigmentosa with and without Darier's sign reported in skin of colour.

Case Reports

Mastocytosis is a disorder characterized by accumulation and proliferation of mast cells in the skin, gastrointestinal tract, liver, spleen, lymph nodes, skeletal system, and bone marrow. According to the World Health Organization (WHO) consensus, mastocytosis in skin (MIS) is classified into three clinical variants: maculopapular, diffuse, and solitary mastocytoma. Maculopapular cutaneous mastocytosis is further subdivided into three types: urticaria pigmentosa, papular/plaque type, and telangiectasia macularis eruptive perstans.[1] Urticaria pigmentosa is the most common form of mastocytosis that often develops in infancy or early childhood. It is usually benign, self-limiting, and spontaneously regresses before adolescence.[2]

Case 1

A 7-month-old male infant with Fitzpatrick type 5 skin presented with a history of asymptomatic multiple dark colored skin lesions over trunk of five months duration [Figure 1]. There was no associated wheeze, flushing, vomiting, or diarrhea. There was no history of hospitalization for drug allergy or anaphylaxis. Family history was not contributory. On examination, there were multiple hyperpigmented macules over the back and chest. Gentle rubbing of the lesions produced wheals suggestive of Darier's sign. Dermoscopic examination was performed using a hand-held dermatoscope (Dermlite DL3,3Gen Inc, USA) and images were captured using the Sony DSC W-800 20.1 MP digital camera (Sony Corp., Tokyo, Japan). Dermoscopy showed a dark brown pigment network which is an exaggeration of the reticular pigment network seen in the normal skin [Figure 2]. The pigment network seen in dermoscopy corresponds to melanin accumulation in the basal layer of the epidermis. Histopathology of lesion over the back showed increased melanization of the basal layer with nests of oval mast cells infiltrating the upper and lower dermis with metachromatic granules visualized using toluidine blue stain diagnostic of urticaria pigmentosa [Figure 3].

Figure 1.

Hyperpigmented macules over the back with positive Darier's sign (wheals on gentle rubbing)

Figure 2.

Polarized dermatoscopy of the back lesion (10×) showing exaggerated dark brown and thick reticulate pigment network (Dermlite DL3,3Gen Inc, USA)

Figure 3.

(a) Histopathology showing increased melanization of the basal layer and oval-to-spindle-shaped cells with granular cytoplasm in the upper and lower dermis (hematoxylin and eosin, 400×). (b) Numerous mast cells with metachromatic granules in the upper dermis and hyperpigmentation of the basal layer (toluidine blue, 400×)

Case 2

A 2-year-old male child with Fitzpatrick type 5 skin presented with multiple brownish skin lesions predominantly over trunk of six months duration [Figure 4]. There was no family history of similar disease and the development of the child was normal. There was no history of urticarial flushing or bullae. On examination, there were multiple hyperpigmented macules over trunk and extremities. There was no wheal formation or erythema on stroking (Darier's sign– negative). There was no hepatosplenomegaly or lymphadenopathy. Dermoscopy showed brownish reticular thick lines in the form of pigment network but relatively lighter than that with positive Darier's sign [Figure 5]. Histopathological examination of lesional skin showed infiltration of numerous mast cells in perivascular and periappendageal location in the upper dermis [Figure 6].

Figure 4.

Hyperpigmented macules over the trunk with negative Darier's sign

Figure 5.

Polarized dermatoscopy of the trunk lesion (10×) showing light brown and thick pigment network (Dermlite DL3,3Gen Inc, USA)

Figure 6.

(a) Histopathology showing increased basal layer pigmentation and mast cells in upper dermis which are oval shaped with moderately abundant eosinophilic cytoplasm, round nuclei, andclumpled chromatin (hematoxylin and eosin, 400×). (b) Mast cells with metachromatic granules in the upper dermis (toluidine blue, 400×)

Discussion

The dermoscopic patterns seen in various forms of cutaneous mastocytosis include: pigment network, reticular vascular pattern, yellow-orange blot, and light-brown blot.[3] Pigment network is a dermoscopic feature that is characteristic of melanocytic lesions. Non-melanocytic lesions like dermatofibroma, solar lentigo, seborrheic keratosis, accessory nipple, and even normal skin exhibits this dermoscopic feature.[4] Urticaria pigmentosa is an addition to the list of non-melanocytic lesions showing pigment network in dermoscopy. Factors secreted by mast cells induce proliferation of melanocytes and melanin production resulting in exaggeration of brown pigment network under dermoscopy.[5] Hence, dermoscopy is a useful method to sub-classify mastocytosis and differentiate it from its close clinical mimics. This is the first case reporting dermoscopy of urticaria pigmentosa reported in dark skin showing exaggerated brown pigment network that is darker than that seen in lighter skin especially with a positive Darier's sign.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.