Solar lentigines are believed to be UVR-induced proliferative responses of the epidermal keratinocytes and/or melanocytes, although the exact mechanism of formation is not completely understood. Ultraviolet B (UVB) exposure is thought to increase expression of keratinocyte growth factor, which thereby induces tyrosinase expression and melanin production in melanocytes. This melanin pigment is then transferred to keratinocytes where there is abnormal pigment retention.
Solar lentigines are more common in those with skin phototypes I-III and a history of multiple sunburns. They are present in 90% of individuals over 60 years of age who are of Northern European descent. They may also be seen in younger individuals with extensive UVR exposure and have been observed as early as 5 years of age in children with xeroderma pigmentosum. They are typically located on sun-exposed skin, including the face, upper chest, shoulders, dorsal arms, and hands. Solar lentigines are asymptomatic although they may enlarge, darken, or remain unchanged over time.
A variant is the psoralen ultraviolet A (PUVA)-induced lentigo, which is seen in approximately 50% of patients with at least 6 years of PUVA therapy and may sometimes be distinguished by large, somewhat atypical melanocytes on histopathology. These may be present on any body surface exposed to PUVA, including the genitalia.
L81.4 – Other melanin hyperpigmentation
72100002 – Solar lentigo
Differential Diagnosis & Pitfalls
- Lentigo simplex – Clinical appearance similar to solar lentigo, but lesions appear earlier in life and are not limited to sun-exposed skin.
- Macular seborrheic keratosis – May be difficult to distinguish from a lentigo; however, lentigines are always macular with intact surface skin lines.
- Melanocytic nevus – Typically well-demarcated; not always on sun-exposed skin.
- Ephelides – Typically smaller, present in childhood in individuals with light skin, can fade with reduced UVR exposure.
- Pigmented actinic keratosis – Tends to have palpable scale and less uniform pigmentation.
- Lentigo maligna melanoma – Lesions tend to be larger, asymmetrical with irregular pigmentation, and may be changing by history or on examination.