Lentigo are benign pigmented macules that result from increased activity of epidermal melanocytes. Lentigo like lesion can be benign or malignant, hence it is important to rule out malignant lesions. While there are many benign lesions that look like lentigo, some malignant lesion can also look like benign lentigo.
Unlike freckles that are commonly seen in lightly pigmented children and fade in the absence of sun exposure, lentigo persistent and do not respond to withdrawal of sunlight. In addition, lentigo can become malignant whereas freckles typically do not. There are two major types of benign lentigo: Simple lentigo and Solar lentigo
Simple lentigo are also known as (lentigo simplex, juvenile lentigo). They are usually small (a few mm to 15 mm) in size with well circumscribed (round or oval) border typically appear during childhood although some children are born with simple lentigo.
Simple lentigo are not induced by sun exposure and therefore have a scattered distribution and often do not show a predilection for sun-exposed areas. However, multiple simple lentigo may be seen in individuals with certain medical conditions such as Addison’s disease or others pathology related to elevated adrenocorticotropic hormone.
Other disease associated with simple lentigo include colon harmatoma like Peutz-Jeghers syndrome.
Solar lentigo are also known as old age spots, senile lentigo, actinic spot or liver spots in different text. However, the term liver spots does not represent a systemic medical disease.
They are larger and appear as tan to dark-brown macules that are flat, ranging from 3 to 20 mm in size with irregular borders
Solar lentigo are proliferation of normal melanocytes secondary to chronic solar damage
These lesions occur most commonly in whites with fair complexion who have a history of chronic sun exposure. Hyperpigmentation may vary from light to dark brown, but is uniform within an individual lesion.
They usually occur on sun exposed areas (such as face, dorsal aspect of hands and forearms, upper chest, and upper back) in response to excessive or chronic sun exposure. In younger individuals, they often appear after an acute sunburn.
Cause and Risk factors
The risk factors of lentigo are due to UV exposure, except for simple lentigo which usually do not occur on sun exposed areas. Aging, fair complexion are also risk factors.
Symptoms and Clinical Presentation
As mentioned, lentigo have very similar appearance to the naked eye and typically require dermatoscopy and biopsy for definitive diagnosis. Differential diagnosis of similar lesion will also be included here.
- Not associated with sun exposure. They develop in early childhood or at birth occurring anywhere in the skin.
- Simple lentigo present as flat macule that are yellow to brown/black in color with even pigmentation
- Usually small but bigger than freckles range from 3 to 15 mm in diameter and well circumscribed with borders that are jagged or smooth.
- Found on sun exposed areas including the face, dorsum of hands, shoulder and neck, typically appear in white adults and increase in number with advancing age.
- Soar lentigo usually appear as flat macular lesion like simple lentigo also with even pigmentation
- They can be similar or large in size than simple lentigo ( few mm to > 1 cm) in diameter and well circumscribed with irregular border/margin
Lentigo Maligna (LM)
- Lentigo Maligna (LM) us considered melanoma in situ defined by the lack of invasion of the dermis.
- LM are flat to elevated lesion like solar lentigo but with darker color and unevenly distributed pigmentation (heterogenous coloration).
- They are have Irregular shap and ill-defined border, smooth, non-scaly and usually have a history of enlargement
Lentigo Maligna Melanoma (LMM)
- One of the 4 types of invasive melanoma, constituting 15% of invasive melanoma)
- LMM have Irregular shape but sharper border, with elevation
- Gradual change and enlargement are usually present.
- They may arise from solar lentigo and appear as macular or elevated lesion. They often have the stuck on velvety, greasy appearance. They are proliferation of normal (non-atypia) keratinocytes and increase in number of melanocytes
- Freckles are smaller (1-2mm, occurring as an autosomal dominant trait, occurring in childhood on sun exposed areas. However, they often fade or fade completely during winter.
- Unlike ephilides (freckles), lentigines are the result of epidermal hyperplasia and of variable proliferation of melanocytes and subsequent melanization.
What to look out for in Lentigo lesions?
- Although most lentigines are benign, they can occasionally transform into lentigo maligna
- If changes in a lentigo such as rapid growth, change in color or surface contour occur, a thorough dermatologic evaluation is warranted and a biopsy may be necessary.
Sometimes, individuals especially children with xeroderma pigmentosum (XP) develop numerous solar lentigo at an unusually early age. In addition, patients with type II oculocutaneous albinism have unusually large, jagged solar lentigos.
In individuals without associated conditions, multiple lentigo may indicate excessive photodamage and increased risk of sun-induced skin cancer.
Lentigo is usually diagnosed clinically but dermatoscope and sometimes biopsy histological examination are necessary to differentiate similar lesion. Dermoscope is usually used to rule out other lesion that can have similar appearance to solar lentigo with the naked eye.
- Simple lentigo are usually clinical diagnosis with dermatoscopy to rule out malignant lesion.
- Dermatoscopy show linear increase of melanocytes at dermal-epidermal junction without atypia.
- Melanocytes increase in number but do not grow in nest.
- Dermatoscope show atypical proliferation of keratinocytes
Lentigo maligna (LM):
- This lesion have variable pigmentation unlike solar lentigo. In addition the borders are irregular, non-scaly with smooth surface and usually have a history of enlargement. Following of the lesion size is important.
- Lentigo maligna is considered melanoma in situ. It may progress to become invasive lentigo maligna melanoma over many years.
Lentigo maligna melanoma (LMM):
- This lesion, which is a sequeale of lentigo maligna, also have irregular border, variable pigmentation. They are considered at type of invasive melaonoma and usually have a raised papule or nodule within the plaque. History of gradual change and enlargement are usually present. Under dermatiscopy, nest of melanocytes at dermal-epidermal junction.
Both LM and LMM have the following features on dermatoscopy exam:
- Asymmetrical pigmented follicular openings (atypical pseudonetwork)
- Dark rhomboidal structures
- Slate-gray globules
- Slate-gray dots
In addition, ABCDE features are usually more alarming and would justify performing a biopsy for definitive diagnosis.
- Asymmetric shape,
- Border irregular,
- Color non-homogenous,
- Diameter > 6mm,
- Evidence of enlargement of change.
Treatment and Management
Benign lesion are usually managed for cosmetic reasons whereas lesions suspicious for malignancy are usually surgically removed for histology evaluation.
Treatment for benign include the following options:
- Chemical peels
- Laser therapy
- Bleaching creams containing hydroquinone.