What are the dermoscopy features and management of solar lentigo (actinic lentigines)?

Dermoscopy of Solar Lentigo

Solar lentigines are benign pigmented lesions that can be diagnosed clinically and dermoscopically by their characteristic features, including light brown homogeneous areas, light brown pseudonetworks, light brown dots and globules, and the absence of malignant features such as asymmetric pigmented follicular openings or slate-gray structures. 1

Key Dermoscopic Features of Solar Lentigines

Solar lentigines display several characteristic dermoscopic patterns that distinguish them from malignant lesions:

• Light brown homogeneous areas are statistically significant benign features 1
• Light brown pseudonetworks indicate benign growth 1
• Light brown globules and dots are characteristic of solar lentigines 1
• Pseudofollicular openings may be present and suggest benignity 1
• Absence of darkening at dermoscopic examination helps differentiate from lentigo maligna 2

Critical Features That Distinguish Solar Lentigo from Lentigo Maligna

The dermoscopic examination must specifically evaluate for malignant features that would indicate lentigo maligna rather than benign solar lentigo:

Features Suggesting Lentigo Maligna (Require Biopsy)

• Asymmetric pigmented follicular openings are sevenfold more likely in lentigo maligna 2, 1
• Gray circles increase likelihood of lentigo maligna sevenfold 2
• Slate-gray dots, globules, or streaks are malignant indicators 2, 1
• Dark rhomboidal structures suggest malignancy 1
• Target-like pattern increases lentigo maligna likelihood sixfold 2
• Darkening at dermoscopic examination is a strong predictor of lentigo maligna 2
• Dark homogeneous areas and dark pseudonetworks indicate malignant growth 1

Features Suggesting Pigmented Actinic Keratosis (Different Entity)

• Hyperkeratosis is thirteenfold more likely in pigmented actinic keratosis 2
• White circles increase likelihood twelvefold 2
• Red rhomboids are sixfold more likely 2

Special Variant: Reticulated Black Solar Lentigo ("Ink Spot" Lentigo)

A specific benign variant exists that can mimic melanoma clinically:

• Black color with wiry, beaded, markedly irregular outline characterizes this variant 3
• Reticulated pattern resembling a spot of ink on the skin 3
• Limited to sun-exposed areas with distribution similar to typical solar lentigines 3
• Usually solitary (median of one lesion per patient) despite numerous typical solar lentigines 3
• Histologically benign with lentiginous hyperplasia, marked hyperpigmentation with "skip" areas, and minimal melanocyte increase 3

Histopathologic Correlation

When biopsy is performed, solar lentigines demonstrate:

• Twofold increase in melanocytes compared to normal photoexposed skin 4
• Twofold increase in epidermal area 4
• Twofold increase in epidermal melanin content 4
• Frequently flattened epidermis on facial lesions (49% of cases) rather than classic rete ridge hyperplasia 4
• No melanocytic atypia and no nests of melanocytes 4

Management Algorithm

When Dermoscopy Shows Benign Features Only

• No biopsy required for typical solar lentigines with characteristic light brown features and absence of malignant criteria 5, 6
• Patient education about sun protection to prevent additional lesions 5
• Annual skin examinations to monitor for new or changing lesions 5

When Dermoscopy Shows Concerning Features

• Excisional biopsy with 2-5 mm margins is preferred to avoid sampling error if any features suggest lentigo maligna 5, 7
• Incisional biopsy may be performed by specialists within a skin cancer multidisciplinary team for large facial lesions where complete excision is impractical 5, 7
• Urgent referral to dermatologist for any suspicious pigmented lesion with asymmetry, border irregularities, color heterogeneity, or evolution 5, 7

Critical Clinical Pitfalls to Avoid

• Do not rely on a single dermoscopic criterion—diagnosis should be based on the combination of specific features rather than isolated findings 2
• Facial solar lentigines frequently lack rete ridge hyperplasia seen at other anatomic sites, which can cause diagnostic confusion 4
• Reticulated black solar lentigines can mimic melanoma due to their dark color and irregular borders, but characteristic features allow clinical diagnosis 3
• Distinguishing solar lentigines from PUVA lentigines is essential in patients with psoralen plus UVA therapy history, as PUVA lentigines are more numerous, darker, and occur in both sun-exposed and protected areas 6
• Lentigines in Peutz-Jeghers syndrome appear on buccal mucosa, a location where solar lentigines never occur 6
• Partial removal or shave biopsies should be avoided as they can result in diagnostic confusion 7