Maria Teresa Corradin1, Mauro Alaibac2,* and Anna Belloni Fortina2

1Unit of Dermatology, General Hospital Pordenone and 2Unit of Dermatology, University of Padua, Via Battisti 206, IT-35128 Padova, Italy. *E-mail: mauro.alaibac@unipd.it

Accepted January 5, 2007.

Sir,

Melanocytic agminated naevus refers to a melanocytic lesion characterized by the presence of a clustering or a circumscribed grouping of lesions confined to a body segment (1–3). Agminated melanocytic naevus differs from naevus spilus by the lack of clinically visible background pigmentation and the histology of a junctional or compound melanocytic naevus (3). Agminated naevi are rarely observed (3–11), compared with agminated blue naevi and agminated Spitz naevi. In this article we describe a case of malignant melanoma arising from an acquired agminated melanocytic naevus.

Case report

A 36-year-old woman was referred to the pigmented lesion clinic of our unit for evaluation of a bluish nodular lesion on the upper portion of her right arm. The lesion was 1 cm in diameter and was surrounded by a red halo. The nodule developed in a 14×4 cm area characterized by the presence of a cluster of melanocytic naevi including the right shoulder and the upper portion of her right arm (Fig. 1). Most of these lesions were papular and no background pigmentation within or surrounding the cluster of naevi was noted clinically or at Wood’s light examination. No personal or family history of melanoma was present. The cluster of naevi appeared at 2 years of age after a hot water burn, which was followed a few months later by sunburn.

Fig. 1. Bluish nodular tumour on the upper portion of the right arm. The nodule is observed in an area including the right shoulder and the upper portion of the right arm characterized by the presence of a cluster of melanocytic lesions.

The nodular lesion was removed and histological analysis revealed a melanoma composed of spindle-shaped malignant cells in vertical growth phase evolving from a pre-existing acquired compound naevus. The Breslow’s thickness of the tumour was 4.4 mm. The malignant cells had a medium mitotic index and ulceration was histologically detected. The patient has shown no evidence of recurrence after 2 years of follow-up.

Discussion

The agminated melanocytic naevus should be distinguished from both naevus spilus and segmental lentiginosis. The distinction between naevus spilus and agminated melanocytic naevus can be made on the presence (naevus spilus) or absence (agminated naevus) of a pigmented background (3). This clinical characteristic can be demonstrated using Wood’s light examination and/or ultraviolet photography (3). However, in some cases the pigmented background can be absent in naevus spilus and in this case the histological analysis is decisive. The histopathological features of naevus spilus are compatible with a lentigo simplex, whereas that of agminated naevus generally shows a junctional or compound melanocytic naevus (3). The differential diagnosis between agminated melanocytic naevi and segmental lentiginosis is based on the histological analysis, which demonstrates a lentigo simplex in segmental lentiginosis and, as already mentioned, a junctional or compound melanocytic naevus in agminated melanocytic naevi.

Several reports of true agminated naevi have been published. Bragg et al. (3) reported four cases of agminated melanocytic naevi and reviewed all the previously published cases defining the clinical and histopathological characteristics of this entity. According to these authors, naevi spili are congenital, whereas agminated melanocytic naevi are acquired and most frequently observed after puberty.

It is of interest to note that the cluster of naevi first became evident at 2 years of age after a hot water burn followed a few months later by severe sunburn. Furthermore, our patient had red hair, fair skin and freckles. Taken together, these observations underline the potential role of severe sunburn in a child with fair complexion in the pathogenesis.

To the best of our knowledge, this is the first report of a malignant melanoma arising from an acquired agminated naevus with the histological features of a common compound melanocytic naevus. There is only one article reporting the apparent development of melanoma in an agminated naevus in a patient with dysplastic naevus syndrome (9). Our clinical observation, together with the lack of knowledge about the biological behaviour of agminated melanocytic naevi, suggests a strict follow-up of this unusual entity.

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