Which histologic findings are characteristic of lentigo?

Updated: Feb 23, 2021
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: William D James, MD  more...
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Lentigo simplex is characterized by a slight-to-moderate elongation of the rete ridges with melanocyte proliferation in the basal layer, increased melanin in both the melanocytes and the basal keratinocytes, and the presence of melanophages in the upper dermis. Lentigines profusa and agminated lentigo are similar in appearance.

Solar lentigines have elongated rete ridges and a proliferation of pigmented basaloid cells, which form buds and strands. These rete ridges may appear flattened. [34]  Ink-spot lentigines are also similar to solar lentigines, except the rete ridges in ink-spot lentigines appear less blunted and more tortuous. No atypia of the melanocytes is present. The solar lentigo has an increased number of melanophages compared with unaffected skin from the same subject. [35] These melanophages were demonstrated to be factor XIIIa-positive dermal dendrocytes.

The melanocytes of PUVA lentigines are increased in number and hypertrophic; they frequently demonstrate cellular atypia. Elongation of the rete ridges and increased pigmentation in the basal cell region is present with transepidermal pigment cell excretion.

Radiation lentigines show increased melanin deposition in basal keratinocytes, cellular or nuclear atypia, increased number of melanocytes, and reduction of rete ridges.

Oral and labial melanotic macules show epithelial hyperplasia with somewhat irregular widening and elongation of the rete ridges. Melanin is increased in the melanocytes and keratinocytes of the basal layer and in the melanophages in the dermal papillae; this increase in melanin indicates pigment incontinence. Vulvar and penile lentigines have similar histologic features except for a slight increase in dendritic melanocytes along the basal layer of the epidermis.

Tanning-bed lentigines resemble PUVA lentigines with the increased density of melanocytes, some of which show mild nuclear atypia. Ultrastructurally, these lesions are similar to those of other forms of lentigo.

Ephelides have an increase in pigment content in the basal cell layer, with neither elongated rete ridges nor increased number of melanocytes.

The myxoma syndromes (ie, LAMB, NAME, and Carney syndromes) show basal layer and, sometimes, spinous layer hyperpigmentation with or without elongation of the rete ridges and melanocytic hyperplasia. Melanocytes may have large dendritic processes, and melanophages may be observed in the upper dermis.

In Peutz-Jeghers syndrome, the lentigines also show marked hyperpigmentation of the basal layer. LEOPARD syndrome involves increased pigment content of the epidermis with an increased number of melanocytes. The melanocytes are filled with melanosomes and are distributed singly or in the form of micronests.

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