Solar lentigo
Lentigo senilis; "age spot"; "liver spot"; senile / actinic lentigo; sun-induced lentigo
Solar lentigines are common, benign, sharply demarcated, light-brown to dark-brown macules of chronically sun-exposed skin, increasing in number from middle age and reaching almost universal prevalence by old age in fair-skinned populations. They are the cutaneous marker of cumulative ultraviolet damage and confer no malignant risk per se. Their importance in skin oncology lies in two domains: clinical and dermoscopic mimicry of lentigo maligna (melanoma in situ on chronically sun-damaged facial skin), where the consequences of misdiagnosis run in both directions (over-treatment of a solar lentigo on the one hand, under-recognition of an early lentigo maligna on the other); and as a marker of cumulative photodamage that places the patient at increased risk of all keratinocyte and melanocytic skin cancers, justifying a full skin check at presentation.
Clinical features
- Well-circumscribed, sharply demarcated, flat, light- to dark-brown macule, usually 2–20 mm.
- Single or multiple — frequently dozens to hundreds in older patients with chronic photodamage.
- Distribution — face (cheeks, forehead, temples), dorsa of hands, forearms, V of neck, scalp (in bald men), shins (in women) — i.e. cumulative UV-exposed sites.
- Onset typically from middle age; prevalence increases steeply with age and UV exposure.
- Background features of photodamage — actinic keratoses, telangiectasias, elastosis, wrinkling.
Dermoscopy
- Reticular pattern — fine, regular, light-brown pigment network with sharply defined "moth-eaten" margins.
- Fingerprint pattern — parallel, curvilinear pigment lines.
- Diffuse light-brown pigmentation with sharply demarcated edges.
- Absent — irregular pigment network, blue-white veil, atypical dots/globules, regression structures.
- Critical caveat — facial sites: solar lentigo on the face shares the dermoscopic field with lentigo maligna; concerning features (asymmetric pigmentation, grey dots, rhomboidal structures, annular-granular pattern, asymmetrical follicular openings) warrant dermoscopic surveillance and a low threshold for biopsy.
Critical differential — lentigo maligna
The most important differential of facial solar lentigo is lentigo maligna (melanoma in situ on chronically sun-damaged skin). Concerning features in a flat pigmented facial macule include:
- Asymmetric pigmentation, particularly variegated browns / greys.
- Grey dots, granules and rhomboidal structures around follicles ("annular-granular" pattern).
- Asymmetrical pigmentation around hair follicles.
- Slow but steady enlargement — note size, photograph, dermoscope.
- Any concerning feature merits biopsy of the most atypical area.
- See lentigo maligna monograph.
Management
- Reassurance — no treatment necessary for the great majority.
- Treatment options for cosmetic concern:
- Topical depigmenting agents (hydroquinone, azelaic acid, kojic acid, retinoids).
- Cryotherapy.
- Q-switched lasers (532 nm Nd:YAG, 694 nm ruby, 755 nm alexandrite); intense pulsed light.
- Chemical peels (glycolic, trichloroacetic acid).
- Biopsy mandatory for any concerning feature (asymmetry, change, atypical dermoscopic features, especially on the face).
- Counsel about photoprotection — broad-spectrum SPF 50+ daily; sun-protective clothing; avoid peak UV; vitamin D supplementation as needed.
- Full skin check — solar lentigines are a marker of cumulative photodamage; opportunity for screening for keratinocyte and melanocytic skin cancers.
References
- Praetorius C et al. Sun-induced freckling: ephelides and solar lentigines. Pigment Cell Melanoma Res; 2014.
- Tanaka M et al. Dermoscopy of solar lentigo, seborrheic keratosis and lentigo maligna on the face. Dermatol Pract Concept; 2018.
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