Lentigo refers to a small, brownish macule that can be observed in various clinical settings thus having different implications with regard to the management of patients bearing one or more lentigines (See Table).
Lentigo simplex is an extremely common, benign melanocytic skin lesion, which can be regarded as the precursor lesion of acquired junctional melanocytic nevus, nowadays called Clark nevus.
Clinically, lentigo simplex involves sun-exposed skin of the trunk and extremities in individuals with white complexion. They usually appear as small, sharply demarcated macules about 3-5 mm in diameter displaying a uniform light-brown or dark-brown color.
Dermoscopic examination of a lentigo simplex is rarely performed, since clinical appearance in conjunction with the clinical setting is virtually diagnostic. When performing dermoscopy, one may observe a delicate, typical pigment network with regularly sized meshes distributed evenly throughout the lesion corresponding to elongated and moderately pigmented rete ridges.
Bolognia, in 1992, described a darkly pigmented type of solar lentigo, clinically simulating melanoma in situ, in a series of patients with Celtic ancestry and numerous actinic lentigines and proposed the term ‘reticulated black solar lentigo (ink spot lentigo)’ [Arch Dermatol 1992]. Furthermore, she pointed out that these lesions were of concern to patients and primary care physicians, because of their dark color and irregular border.
The clinical setting of reticulated lentigo is rather stereotypical, because the lesion is nearly exclusively restricted to white individuals with type I or II skin and a history of severe sunburns with blister formation. As a rule, the reticulated lentigo is surrounded by numerous sun-induced freckles. It is usually situated on the back and occurs as a solitary black lesion with wiry or beaded, markedly irregular outline thus clinically simulating melanoma in situ.
Dermoscopically, the reticulated lentigo reveals a distinctive appearance, characterized by a bizarre and asymmetric reticular pattern with markedly thickened pigment network showing irregular and wide meshes. This pathognomic dermoscopic appearance reflects the particular epidermal architecture marked by pronounced pigmentation of the tips of elongated rete ridges and by the nearly complete absence of epidermal pigmentation covering the suprapapillary plates.
Solar lentigo (synonyms: lentigo actinica, senile lentigo) is a circumscribed, brownish macule occurring usually as numerous lesions on chronically sun-damaged skin. Solar lentigo may be regarded as the precursor lesion of the reticulated type of seborrheic keratosis, because of the frequent association of these two pigmented skin lesions on clinical and histopathologic grounds.
Clinically, solar lentigines usually occur as numerous lesions on severely sun-damaged skin in elderly individuals, but may even develop in the first decades of life. They are mainly found on the dorsum of hands, extensor surfaces of the forearms, and the face. The lesions may vary in size up to a few cm in diameter and are characterized by markedly irregular outlines with various shades of coloration ranging from light brown to dark brown.
As mentioned before in the context of lentigo simplex, the clinical diagnosis of solar lentigo is very easy in most instances and the dermoscopic examination not really relevant. In our opinion, the dermoscopic examination of solar lentigines is helpful particularly in order to better understand the differential diagnostic difficulties which may arise with melanoma in situ on severely sun-damaged skin. Dermoscopically, solar lentigines on the dorsum of the hands, extensor surfaces of the arms, and the back, reveal a delicate, sharply demarcated reticular pattern with regular meshes and thin lines.