What is solar lentigo?
Solar lentigo is a harmless patch of darkened skin. It results from exposure to ultraviolet (UV) radiation, which causes local proliferation of melanocytes and accumulation of melanin within the skin cells (keratinocytes). Solar lentigos or lentigines are very common, especially in people over the age of 40 years. Sometimes they are also known as an “old age spot” or “senile freckle”.
What does a solar lentigo look like?
A solar lentigo is a flat, well-circumscribed patch. It can be round, oval or irregular in shape. Colour varies from skin-coloured, tan to dark brown or black, and size varies from a few millimetres to several centimetres in diameter. They can be slightly scaly.
Solar lentigines are found as groups of similar lesions on sun-exposed sites, particularly the face or the back of hands. They occur in light and dark skin but tend to be more numerous in fair-skinned individuals. Solar lentigines may be seen in younger patients often following an acute episode of sunburn
They are commonly on face in younger patients and they appear on face, back of hand and forearms in older person.
How is a solar lentigo diagnosed?
Solar lentigo is often diagnosed on its clinical appearance. On occasion, it can be difficult to differentiate an irregular solar lentigo from melanoma, a potentially dangerous form of skin cancer, and the term atypical solar lentigo may be used.
- Shows homogenous pattern & colouration with commonly has a particular “moth-eaten” or “Jelly-like” edge.
- They can show diffuse colouration with circular hypopigmented follicular openings, called pseudo-network (like in seborrheic keratosis)
Histological features of solar lentigo
There is linear increase in melanocytes at the dermo-epidermal junction with extension of rete ridges to form bud-like processes. There is increased deposition of melanin in the basal keratinocytes. Sometimes there are large melanocytes that are monomorphous, equidistant from one another and unassociated with nests of melanocytes. Solar elastosis is present in the papillary dermis, with or without incontinence of pigment (melanophages).
Changes within solar lentigo
Seborrheic keratoses may arise within solar lentigines. This results in localised thickening and change in texture within the lentigo.
Solar lentigines may become inflamed, when they are called lichenoid keratoses or lichen-planus like keratoses (due to the pattern of inflammation seen on histopathology). Lichenoid keratoses gradually disappear.
Clinical differential diagnosis:
lentigo maligna may be clinically mistaken as solar lentigo especially on face as they may show the same features: regular & homogenous appearance, small size, lacking the ABCD signs of malignancy.
Dermatocopy is helpful in this distinction. Dermatoscopic features of lentigo maligna include asymmetrical pigmented follicular openings, and slate-grey aggregated dots around the hair follicles proceeding to dark-brown or black streaks.
What treatments are available for solar lentigo?
Bleaching agents such as hydroquinone are not effective.
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