Appearance

One study of Caucasian women found that lentigines were signs of photo-damage whereas there was a genetic component in true freckles.^[1] 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.^[2] 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 getting younger with increasing sun exposure. The colour may vary from yellow-brown to black.
• 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 (UVA) treatment (PUVA) 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:^[2] 

• LEOPARD - lentigines, electrocardiographic conduction defects, ocular hypertelorism, pulmonary stenosis, abnormal genitalia, retardation 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; and testicular tumours.

Differential diagnosis^[2]

• Actinic keratosis.
• Ephelides (freckles) - get darker after sun exposure.
• Seborrhoeic keratosis.
• Xeroderma pigmentosum - an autosomal recessive condition in which the DNA fails to repair itself after skin damage.
• Melanoma - tends to have more variation in colour density within the lesion than a lentigo.
• Lentigo maligna^[3]  - seen mainly on the sun-exposed areas of the face and neck in the elderly, is slow-growing and usually quite large (>20 mm). 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 and occurs in approximately 5% of patients. Identifying lesions that require referral is not easy but worrying signs include changes in size or colour, itching, burning, bleeding, or pain. The ABCDE rule of melanoma may be helpful:
  • A - Asymmetry.
  • B - Border irregularity.
  • C - Colour variegation.
  • D - Diameter greater than 6 mm (the end of a pencil head), although melanoma can occur in lesions less than 6 mm.
  • E - Enlargement.

See separate article Malignant Melanoma of Skin for more details.

Investigations^[2] 

• Biopsy and histology may be used to differentiate the various types of lentigines.
• A dermatoscope is is occasionally used in the diagnosis of solar lentigo.

Primary care management

• Unsightly lesions of face can be lightly frozen, which often improves the cosmetic result.
• Tretinoin is occasionally employed to lighten lesions (unlicensed use).^[4] 

Secondary care management^[2]

• Cryotherapy is used for isolated lentigines and is more effective than 40% trichloracetic acid for the treatment of solar lentigines. Some studies have reported that cryotherapy is painful but analysis suggests this is more to do with the operator and the technique employed rather than the treatment per se. ^[5] 
• One study showed that a mid-depth chemical peel with phenol resulted in greater patient satisfaction with the end result than cryotherapy for the treatment of solar lentigo but resulted in more pain, erythema and a longer healing time.^[6] 
• 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 local chemical peel or lasers (Q-switched Nd:YAG or ruby) are effective when available.^[2][8]

Prognosis

Lentigines tend to get worse over time but do not go malignant.

Prevention^[2] 

• New lesions can be prevented to some extent by sun avoidance, use of sunblock creams and keeping on a shirt when outside in the sunshine.
• 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.