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Desmoplastic hairless hypopigmented nevus (DHHN). A distinct variant of giant melanocytic nevus

European Journal of Dermatology. Volume 15, Number 6, 451-3, November-December 2005, Genes and skin

Summary

Author(s) : María del Carmen Boente, Raúl A Asial , Centro de Investigaciones Dermatológicas, Tucumán, Argentina.

Summary : Desmoplastic hairless hypopigmented nevus (DHHN) is the name Ruiz-Maldonado et al. gave to a new variant of giant congenital melanocytic nevus characterized clinically by a hard ligneous consistency, absence of hair and progressive loss of pigment. Histologically, dermal fibrosis consistent with desmoplasia is a predominant feature. We describe a 6-year-old boy with a hard hairless pigmented congenital nevus involving the lumbosacral area, buttocks, perineum and scrotum. During the first years of life, the nevus showed a progressive reduction in colour, size and consistency. These changes continued until the age of four when a well-demarcated tumour appeared, within the nevus, on the right buttock. Resection of this outgrowth was performed. Histologically, nevus cells of normal appearance between thick collagen bundles were present. Immunostaining revealed S100 +, Vim +, HMB45 – results. The nevus has continued to involute to date. An immune response against the melanocytes of the nevus may explain this type of evolution.

Keywords : congenital melanocytic nevus, desmoplastic hairless hypopigmented nevus, nevus

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ARTICLE

Auteur(s) : María del Carmen Boente, Raúl A Asial

Centro de Investigaciones Dermatológicas, Tucumán, Argentina

accepté le 24 Août 2005

Giant congenital melanocytic nevi (GCMN) are rare congenital pigmented tumours present in 1:20,000 live births. They are usually dark brown or black hairy lesions measuring ≥ 20 cm in diameter with a consistency similar to the adjacent skin [1-3]. In general they show a patchy distribution without midline demarcation [4].Diverse cutaneous changes within the nevus (hypoplasia of the subcutaneous fat, neuroid proliferations, halo phenomenon, etc.), as well as the rare spontaneous regression of the lesion have been described [5, 6].Ruiz-Maldonado et al. [7] reported a new type of GCMN showing a sclerodermoid reaction that progressively destroys the melanocytic cells. He gave this nevus the name: “Desmoplastic Hairless Hypopigmented Naevus (DHHN)”.We report a new case of this type of nevus with unusual clinical features.

Case report

A 6-year-old boy was first seen at birth with a GCMN involving the lumbosacral area, buttocks, perineum and scrotum. At birth, the lesion was hairless, dark red-brown in colour with irregular mottled borders, and of a hard ligneous consistency ( (figure 1) ). A punch biopsy showed an increased number of melanocytes in the basal layer. The deep dermis showed an increased number of nevus cells of epithelioid configuration and melanophages intermingled with thick collagen bundles. Adnexal structures were absent ( (figure 2) ).

During his first year of life a progressive reduction in colour, size and consistency of the nevus was noted. Intense pruritus and xerosis were the only constant complaints.

This progressive improvement continued until the age of four when a small, hard, well-demarcated dermal tumour appeared on the right buttock ( (figure 3A) ). The tumour became exophytic in few weeks, reaching the size of 2 × 2 cm in diameter. It was pedunculated and showed a granular surface (( (figure 3B) ). Resection of this outgrowth was performed. Histopathological examination showed nevus cells of spindle and epitheliod appearance, without atypia, between thick collagen bundles ( (figure 4A and 4B) ). Immunostaining results showed S100 +, Vim +, HMB45 (–), and CD34 (–).

During the 2 year follow up, no other tumours appeared. A progressive loss of pigment and induration was observed, and areas of normal-appearing skin became evident within the tumour ( (figure 5) ).

Discussion

Giant congenital melanocytic nevi (GCMN) are important congenital tumours due to their significant cosmetic disfigurement as well as their potential malignant transformation [3]. Although spontaneous regression of GCMN has rarely been described, the involution is usually not associated with sclerosis or hair loss [7, 8]. Ruiz-Maldonado et al. [7] described a unusual type of congenital hairless melanocytic nevus showing a peculiar form of spontaneous regression and named it “Desmoplastic Hairless Hypopigmented Naevus (DHHN)”.

Among the clinical features of this particular type of GCMN are the hard indurate texture, the absence of hair, the progressive loss of pigment, an irregular mottled erythematous border and pruritus (table 1)( Table 1 )[7]. Histological features are dermal fibrosis, desmoplasia, paucity of melanocytes, atrophic or absent hair follicles and atrophic or absent sebaceous glands (table 2)( Table 2 )[7].

A nodular growth in a GCMN usually raises suspicion of malignant transformation. Melanomas inside GMCN develop as deep focal nodules of rapid growth. Many have already metastasized at the diagnosis [3].

In DHHN the progressive desmoplasia with melanocyte depletion resulting in pigment loss may indeed imply a reduced risk of malignant transformation. Patee et al. [5] reported a case of giant congenital nevus with a progressive sclerodermoid reaction and considered that an immune reaction against melanocytes of the nevus may explain this phenomenon. We assume that in this type of nevus, a tumour growth within the nevus may represent another type of immunologic reaction without malignant probability.

So far, the number of reported cases of DHHN is rather limited. Future reports may show whether the emergence of a pedunculated benign tumor within DHHN, as noted in the present case, is an exceptional feature or not during the evolution of this type of nevus.
Table 1 DHHN: clinical features

• Giant congenital melanocytic naevus

• Hard indurate texture

• Alopecia

• Progressive loss of pigment

• Irregular mottled border

• Pruritus

Table 2 DHHN: histopathological features

• Dermal fibrosis – Desmoplasia

• Paucity of melanocytes

• Atrophic or absent hair follicles

•Atrophic or absent sweat and sebaceous glands

References

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2 Kopf AW, Bart RS, Hemnessey P. Congenital nevocytic nevi and malignant melanoma. J Am Acad Dermatol 1979; 1: 123-30.

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4 Happle R. Mosaicism in human skin: Understanding the patterns and mechanism. Arch Dermatol 1993; 129: 1460-70.

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6 Caradona SA, Skidmore R, Gupta A, Bush CH, Ford MJ. Giant congenital melanocytic nevus with underlying hypoplasia of the subcutaneous fat. Ped Dermatol 2000; 17: 387-90.

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