To the Editor:

Nevus spilus, also known as speckled lentiginous nevus or zosteriform lentiginous nevus, is a melanocytic lesion that presents as a light-brown circumscribed background macule or patch that contains numerous more darkly pigmented macules or papules within its borders. Histologically, the background macule is due to lentiginous melanocyte hyperplasia at the dermoepidermal junction, while the more intensely pigmented lesions are melanocytic junctional nevi or combined nevi. Nevus spilus can be congenital but is more commonly an acquired lesion; it has a benign behavior, though a few cases of melanoma arising on a nevus spilus have been reported.1 Blue nevi are bluish-colored lesions formed by an intradermal proliferation of melanocytes. They usually present as a single, acquired lesion, but very rarely can arise as multiple lesions grouped in a well-defined area, not usually larger than 10cm in diameter; they are then called agminated blue nevi.2 The combination of agminated blue nevi and nevus spilus is rare.3

A 79-year-old woman was seen for an asymptomatic pigmented lesion that had been present on the posterior surface of her right lower leg since birth (Fig. 1). Physical examination revealed a 10×6cm plaque formed of a light-brown macule that contained numerous dark-brown papules and bluish lenticular lesions within its borders. Dermoscopy of the brownish papules showed a globular melanocytic pattern, while the bluish papules presented a homogeneous blue pattern (Fig. 2).

Figure 1.

Pigmented lesion measuring 10×6cm on the posterior surface of the right lower leg. The lesion was formed of a background of a light-brown macule that contained multiple dark-brown macules and papules within its borders, together with various bluish lenticular elements.

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Figure 2.

Dermoscopy image showing the collision of a blue nevus (presenting a homogeneous blue pattern) with several melanocytic nevi (showing a typical globular pattern).

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Histology of the different biopsies taken from the pigmented plaque revealed a lesion with a combined pattern (Fig. 3). A proliferation of spindle-shaped melanocytes with no atypia was observed in the dermis, accompanied by melanophages, a characteristic finding in blue nevus. Melanocyte proliferation with a lentiginous pattern was also seen at the dermoepidermal junction; this correlated clinically with the background light-brown macule. Finally, a third component formed of nests of melanocytes with correct maturation and with no architectural atypia was observed in the superficial dermis. These nests produced the dark-brown macules and papules of the nevus spilus.

Figure 3.

Histopathology revealed a combined lesion, with findings characteristic of a blue nevus (a dermal proliferation of spindle-shaped melanocytes associated with melanophages) and findings corresponding to nevus spilus (a lentiginous proliferation of melanocytes at the dermoepidermal junction and nests of melanocytes with no atypia in the superficial dermis). Hematoxylin and eosin, original magnificationx10.

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The definitive diagnosis was nevus spilus associated with agminated blue nevi. The patient stated that the nevus spilus had been present since birth, whereas the bluish lesions had appeared progressively throughout her life, with a significant increase in the number of blue nevi in recent years.

Blue nevus usually arises as a solitary lesion, although it can rarely occur in clusters in an agminated pattern.4 Nevus spilus can be associated with blue nevus, with common melanocytic nevus, or with Spitz nevus. The association of nevus spilus and agminated blue nevi is a rare combination, with few cases reported in the literature.3,5 Kawamura5 presented a case and defined 3 histologic variants of this entity: type I, a combination of blue nevus and cellular nevus; type II, a combination of blue nevus with nevus spilus; and type III, a combination of blue nevus and fibromatous or myomatous nevoid formation. There is controversy regarding the cause of the association. Some authors consider that this is a random phenomenon,5 while others believe that nevus spilus provides a favorable environment for the growth of other nevi.3 The risk of malignant change is low in nevus spilus, although cases of melanoma arising on this pigmented lesion have been reported in the literature.6–8 Our case presents the rare combination of nevus spilus with agminated blue nevi and, despite the clinical and dermoscopic diagnosis, it was necessary to perform several biopsies of the pigmented plaque to exclude a diagnosis of melanoma.

We have presented a case of Kawamura type II blue nevus, highlighting the need to perform periodic clinical control of pigmented lesions and suggesting the possibility of monitoring this type of lesion using digital dermoscopy.