Lentigo

What is a lentigo?

Lentigines (plural of lentigo) are flat brown lesions which do not darken following sun exposure (thus differentiating them from ephelides, or true freckles).

Appearance¹

One study of Caucasian women found that lentigines were signs of photo-damage whereas there was a genetic component in true freckles.² They may be any size from 5-20 mm and may be irregular in shape. They occur over the shoulders in young people, especially those who have had a lot of sun exposure and in the elderly on the sun-exposed sites such as the dorsum of the hands and forearms, the face and the neck.

The histopathology may include hyperplasia of the epidermis and pigmentation of the basal layer. A number of different types are found:

• Lentigo simplex - the most common type, mainly seen in children and not associated with sun exposure. The spots are 5-15 mm in diameter.

• Solar lentigo - related to sun exposure. Seen on skin normally exposed to sunlight (eg, face, hands), they are benign lesions, <5 mm in diameter but may merge to form larger spots. Former peak age of 30-50 is becoming younger with increasing sun exposure. The colour may vary from yellow-brown to black.
  

  Solar lentigo

  

  By Alain Gérard, CC BY-SA 4.0, via Wikimedia Commons
  
  

• Ink spot lentigo - this lesion, so called because it resembles a spot of ink, is a benign lesion limited to sun-exposed areas. They are usually solitary lesions and may be mistaken for melanomas.

• PUVA lentigo - these brown macules can appear six months or more after the start of psoralen combined with ultraviolet A (PUVA) treatment for psoriasis in areas exposed to treatment. The macules are usually 3-8 mm in diameter and persist for 3-6 months after treatment has finished. There is also a larger stellate form (which can be up to 3 cm in diameter) which may persist for two years or more.

• Radiation lentigo - this appears after a single large exposure to radiation (of Chernobyl proportions rather than post-radiotherapy). There may be other histological signs of radiation damage, such as epidermal atrophy and subcutaneous fibrosis. The malignant potential for such lesions is not known.

• Sunbed lentigo - lentigines can appear rapidly after intense exposure, or they may appear after long-term use. They are 2-5 mm in diameter and are most common on the anterior aspects of the arms and legs.

• Labial and oral melanotic macules - labial macules usually appear as single lesions on the vermillion of the lower lip. Oral lesions occur on the gingival and buccal mucosa, palate and tongue.

• Genital lentigo - in men, this can present as a tan to dark-brown macule anywhere on the glans, shaft or corona. They can achieve a size of 15 mm. In women, lentigines can occur anywhere on the genital mucosa and are usually between 5-15 mm in size.

• Lentigines profusa - in this condition, there are widespread lentigines over the arms, legs and genitalia. There are no trigger factors or associated abnormalities (thus differentiating them from a number of lentigo-associated syndromes - see below). The lesions can be 5 mm-2 cm in diameter. The appearance is of dark brown or black freckles but with a more generalised distribution.

• Agminated lentiginosis - in this condition, which can be associated with a number of childhood diseases, lentigines appear in a sharply demarcated distribution which often follows the outline of dermatomes. They are tan or dark brown in colour and may be present at birth or develop in early childhood.

A number of lentigo-associated conditions can occur:

• LEOPARD - lentigines, electrocardiographic conduction defects, ocular hypertelorism, pulmonary stenosis, abnormal genitalia, restriction of growth, deafness.

• Peutz-Jeghers syndrome - gastrointestinal polyps and pigmented macules.

• Laugier-Hunziker syndrome - a variable number of pigmented macules appearing commonly around the oral mucosa or lower lip and in other areas.

• Myxoma syndromes - a group of disorders including:
  

  • LAMB - lentigines, atrial myxomas, mucocutaneous myxomas and blue naevi.

  • NAME - naevi, atrial myxoma, myxoid neurofibroma and ephelides.

  • Carney's syndrome - cardiac, cutaneous and mammary myxomatous masses; lentigines; blue naevi; endocrine disorders; testicular tumours.

Differential diagnosis³

• Actinic keratosis.

• Ephelides (freckles) - become darker after sun exposure.

• Seborrhoeic wart.

• Xeroderma pigmentosum.

• Melanoma of the skin.

• Lentigo maligna - seen mainly on the sun-exposed areas of the face and neck in the elderly; it is slow-growing and sometimes grows to a size of several centimetres. Their size and site differentiates them from lentigines. Lentigo maligna is a pre-cancerous condition. Conversion to a lentigo maligna melanoma can take from a few months to up to 15 years. Transformation to malignancy is lower than in other forms of melanoma, occurring in approximately 5% of patients. However, the risk is higher in larger lesions with a risk of 50% in lesions larger than 4 cm. Identifying lesions that require referral is not easy but worrying signs include changes in size or colour, itching, burning, bleeding, or pain.⁴ The ABCDE rule of melanoma may be helpful:

  • Asymmetry.

  • Border irregularity.

  • Colour variegation.

  • Diameter greater than 6 mm (the end of a pencil head), although melanoma can occur in lesions less than 6 mm.

  • Enlargement.

Lentigo maligna

By kilbad, CC BY 3.0, via Wikimedia Commons

See the separate Malignant Melanoma of Skin article.

Investigations⁵

• Biopsy and histology may be used to differentiate the various types of lentigines.

• A dermatoscope is occasionally used in the diagnosis of solar lentigo.

• The diagnosis of lentigo maligna has been improved by the use of reflectance confocal microscopy (a non-invasive imaging technique that enables in vivo visualisation of the epidermis down to the papillary dermis) and immunohistochemical stains.

Primary care management of lentigo

• Unsightly lesions of the face can be lightly frozen, which often improves the cosmetic result.

• Tretinoin is occasionally employed to lighten lesions (unlicensed use).⁶

• Any treatment which has a purely cosmetic aim may not be available on the NHS.

Secondary care management of lentigo

• Cryotherapy can be used for isolated lentigines. One study found it was more effective than 40% trichloracetic acid for the treatment of solar lentigines although the difference was not significant.

• Lasers are useful for a variety of lentigines. Aggressive therapy for using quality-switched lasers is effective in the treatment of solar lentigines but carries the risk of post-inflammatory hyperpigmentation (PIH). For darker skin types, less intensive irradiation reduces this risk, with no reduction in efficacy.⁷

• Intense pulsed light (IPL) is another option.

When to refer

• For doubt over diagnosis and for diagnostic biopsy.

• When treatment is required but cannot be provided within primary care - eg, treatment with lasers (Q-switched Nd:YAG or ruby) are effective when available.⁸

Prognosis

Lentigines tend to worsen over time but do not become malignant.

Lentigo prevention¹

• New lesions can be prevented to some extent by sun avoidance. Clothing is more effective than sunscreens.

• Avoiding the excessive use of sunbeds helps to prevent tanning-bed lentigines.

• Avoidance of a large single dose of ionising radiation helps to prevent radiation lentigines.