Lentigo

Background

A lentigo is a small, sharply circumscribed, pigmented macule surrounded by normal-appearing skin. Histologic findings may include hyperplasia of the epidermis and increased pigmentation of the basal layer. A variable number of melanocytes are present; these melanocytes may be increased in number, but they do not form nests. Lentigines may evolve slowly over years, or they may be eruptive and appear rather suddenly. Pigmentation may be homogeneous or variegated, with a color ranging from brown to black.

Multiple clinical and etiologic varieties exist. The distinction of a lentigo from other melanocytic lesions (eg, melanocytic nevi, melanoma) and its role as a marker for ultraviolet damage and systemic syndromes is of major significance.

A case-controlled study in France comparing 145 adults with multiple solar lentigines on the upper back and 145 matched control subjects found that multiple solar lentigines on the upper back and shoulders of adults may serve as clinical markers of past severe sunburn and may be used to identify a population at higher risk of developing cutaneous melanoma.^[1]

The concept of “unstable solar lentigos” evident as irregularly pigmented macules on the background of chronic sun damage has been considered alongside the idea that they may have malignant potential.^[2]

Note the images below.

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Woman with solar lentigo.

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Close-up view of a woman with solar lentigo.

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Pathophysiology

Long-term exposure to ultraviolet radiation and pollution as one ages may induce the common solar lentigo.^[3] Depending on the type of lentigo present, a solitary lesion or multiple lesions can occur anywhere on the body. Some lentigines have associated systemic manifestations that accompany the skin lesions, such as the LEOPARD syndrome.

A Japanese microarray analysis evaluation of solar lentigo in 16 adults demonstrated up-regulation of genes related to inflammation, fatty-acid metabolism, and melanocytes and down-regulation of cornified envelope-related genes.^[4] The researchers suggested solar lentigo may be induced by the mutagenic effect of repeated past UV light exposures, leading to characteristic enhancement of melanin production.

Little is known about the genetic basis of human solar lentigines, which were analyzed for potential FGFR3 and PIK3CA mutations. FGFR3 mutations were detected in 5 (17%) of 30 solar lentigines, and PIK3CA mutations were detected in 2 (7%) of 28 solar lentigines, suggesting that FGFR3 and PIK3CA mutations are involved in their pathogenesis and further substantiating previous speculations that UV exposure may be a causative factor for FGFR3 and PIK3CA mutations in human skin.^[5] Lentigines, which develop earlier and are more pronounced in Japanese than in German women, have been found to correlate with variants in the SLC45A2 gene.^[6]  Extensive lentigo simplex, linear epidermolytic nevus, and epidermolytic nevus comedonicus were linked with a somatic mutation in KRT10.^[7]

The LEOPARD syndrome may be associated with a mutation in the PTPN11 gene at Thr468Met.^[8]

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Etiology

The cause of lentigo formation depends on the type of lesion, as follows:

• The cause of lentigo simplex is unknown. Case reports have described simple lentigines developing in children after use of topical tacrolimus for atopic dermatitis.^[9]
• Solar lentigo and ink-spot lentigo are associated with sun exposure in fair-skinned people.
• PUVA lentigines^{[10, 11, 12]} are associated with PUVA therapy in patients with psoriasis.
• Radiation lentigo is caused by local high-dose irradiation.^[13]
• Genetic factors may be involved in other forms of lentigines, including XP, LEOPARD syndrome, Peutz-Jeghers syndrome, and inherited patterned lentiginosis.

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Epidemiology

Frequency

United States

In America, solar lentigines are observed in as many as 90% of whites older than 60 years and in 20% of whites younger than 35 years. Psoralen plus UVA (PUVA) lentigines are noted in almost one half of individuals with psoriasis who receive PUVA therapy for at least 5 years. They may also be evident in resolving psoriatic plaques in individuals, including children, who did not receive UV therapy.^[14]

Lentigo simplex is the most common form of lentigo, but its frequency has yet to be determined. Alper and Holmes^[15] noted multiple lentigines in 91 (18.5%) of 492 black newborns and 1 (0.04%) of 2682 white newborns; however, histologic confirmation of these lesions was lacking.

International

Lentigines are observed worldwide. The incidence depends on the type of lesion.

Seborrheic keratosis and lentigo solaris were found to be increased on the driver side of the face in an evaluation of truck drivers in Turkey assessing the effects of UV light.^[16]

Race

Solar lentigines are more abundant in fair-skinned whites than in dark-skinned individuals, in whom the disease is distinctly uncommon because they have a greater amount of natural pigment that provides some degree of photoprotection. Lentigines, prominent skin signs of aging, develop earlier and are more pronounced in Japanese than in German women.^[6]

Inherited patterned lentiginosis can occur in blacks, particularly those with mixed American Indian heritage and those with relatives with red hair.^[17]

Ephelides, PUVA lentigines, tanning-bed lentigines, vulvar lentigines, ink-spot lentigines,^[18] oral and labial melanotic macules, and Laugier-Hunziker syndrome are also more common in people with light skin than in those with dark skin. Ink-spot lentigo occurs in patients of Celtic ancestry.

Acral lentigines are more common in dark-skinned individuals, but they may also be present in light-skinned individuals.

Sex

PUVA lentigines are more common in men than in women. Tanning-bed lentigines and oral and labial melanotic macules are more common in women than in men.

Age

Lentigines can appear in both children and adults; however, children are more likely to have genetically associated lesions such as those of Peutz-Jeghers syndrome.

Adults are more likely to acquire lesions due to chronic exposures, which cause solar lentigo for example.

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Prognosis

Lentigines are benign by nature.

In patients in whom lentigines are associated with systemic abnormalities or complications, the prognosis may depend on the severity of the associated conditions.

Treatments with cryosurgery, lasers, and/or topical creams have been successful (see Medical Care).

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Patient Education

Patients should be advised about the risks of sun exposure and the use of tanning beds.

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History

The initial appearance of lentigines varies widely and depends on the following:

• Race
• History of exposures
• Genetic predisposition
• Other factors, depending on the type of lentigo

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Physical Examination

The physical appearance and morphology of lentigines depend on the type of lesion.

Lentigo simplex

Lentigo simplex (eg, simple lentigo, juvenile lentigo) is the most common form of lentigo. Lentigo simplex is not induced by sun exposure, and it is not associated with systemic disease. Clinically, the lesions are round or oval asymptomatic macules that are 3-15 mm in diameter. Their margins can be either jagged or smooth. Pigmentation is evenly distributed, with a color ranging from brown to black. The lesions are few in number and may occur anywhere on the skin or mucous membranes. The lesions usually appear first in early childhood, but they can also be present at birth or develop later.

Multiple dysplastic nevi and lentigines were reduced in number in a patient with familial gastrointestinal stromal tumors syndrome after treatment with imatinib mesylate.^[19] The effect of effect of imatinib on pigmentation is not well understood.

Solar lentigo

Solar lentigo (eg, actinic lentigo, senile lentigo, sun spot, liver spot) is the most common benign sun-induced lesion that occurs in sun-exposed areas. Solar lentigo most commonly appears on the face, arms, dorsa of the hands, and upper part of the trunk. The spots initially are smaller than 5 mm in diameter. The surface of the lesions is either flat or depressed, and it may be split by fine wrinkles.

The lesions are usually brown, but the color may range from yellow-tan to black. Older lesions are often dark brown or brownish black. Solar lentigines slowly increase in number and in size. Many lesions eventually coalesce to form larger patches. Although these lesions are most common in individuals aged 30-50 years, they are now seen in younger individuals because of their increased exposure to sun tanning and the use of artificial sources of UV light. Although they are often called liver spots, they are not a manifestation of systemic disease.

In vivo reflectance confocal microscopy may show solar lentigines having increased melanin and hemoglobin levels and a higher rate of epidermal proliferation. Deformation and the number of the hyperrefractive dermal papillary rings may increase significantly over the 5-year time span, with the lentigo size enhanced and color darkened.^[20]

Ink-spot lentigo

Ink-spot lentigo (ie, reticulated black solar lentigo) can be distinguished by a wiry or beaded, markedly irregular outline; these lesions occur in patients of Celtic ancestry. The benign lesions have a reticulated pattern, and most lesions resemble a spot of ink. The distribution is limited to sun-exposed areas of the body, similar to that of solar lentigo; however, in contrast to solar lentigines, patients usually have only 1 ink-spot lentigo. The most common presentation includes 1 ink-spot lentigo among an extensive number of solar lentigines.

These lesions can also be distinguished from the darkly pigmented PUVA lentigo by their more reticulated or beaded pattern and multiple central and peripheral skip areas. Ink-spot lentigines can initially suggest melanoma because of their dark color, irregular border, and limited number; however, further investigation, which may include biopsy, reveals the characteristic features of these benign lesions.

PUVA lentigo

PUVA lentigo is a persistent, pale brown macule appearing 6 months or longer after the start of PUVA therapy for psoriasis. The lesions resemble solar lentigines, but they often have more irregular borders and may mimic ephelides. The occurrence of lesions is closely associated with greater cumulative doses of PUVA, and the lesions may occur on all treatment sites. The most common areas include the upper part of the chest and back, groin, buttocks, glans penis, and penile shaft. The axillae, palms, soles, and gluteal cleft are spared. The lesions vary from 3-8 mm in diameter, but stellate lesions can be as large as 3 cm in diameter. The lentigines may persist for 3-6 months after therapy is discontinued. In contrast, stellate lesions can persist longer than 2 years.

Radiation lentigo

Radiation lentigo resembles UV-induced lentigo, but it often includes other histopathologic signs of long-term cutaneous radiation damage such as epidermal atrophy, subcutaneous fibrosis, keratosis, and telangiectasias. The presence of a radiation lentigo is considered an indicator of a prior cutaneous exposure to a large single dose of ionizing radiation (eg, exposure during the Chernobyl nuclear accident). These lesions have not been shown to occur after local fractionated radiation therapy. Radiation lentigines are persistent and typically occur 4 months or longer after the initial exposure. The malignant potential of the lesions is unknown; however, the induction of melanoma by ionizing radiation has never been proven.

Tanning-bed lentigines

Tanning-bed lentigines^{[21, 22, 23]} usually occur in women with a history of tanning-bed use. Tanning-bed lentigines are similar to PUVA lentigines, except psoralens are not involved. The site of tanning-bed lentigines is primarily acral despite whole-body exposure. The most common areas include the anterior aspects of the arms and legs, but they can also occur on the neck and chest. The size of the lesions varies. The lesions are usually 2-5 mm in diameter, with color ranging from dark brown to black. Some lentigines may coalesce and enlarge. Pigmentation of the lesions may be uneven, with irregular or stellate shapes. The lesions can appear abruptly after intense tanning, or they can appear after prolonged (eg, 1 y) regular use of tanning beds. The malignant potential of the lesions is unknown.

Oral and labial melanotic macules

Oral and labial melanotic macules are similar to each other. Labial lesions almost always occur on the vermilion of the lower lip, and their color ranges from brown to blue to blue-black. Occasionally, variegated pigmentation occurs. The lesions are usually solitary, symmetric, and asymptomatic. Oral lesions can appear on the gingiva, buccal mucosa, palate, and tongue. Usually, oral and labial lesions have a diameter smaller than 4 mm. The individual's age at onset ranges from 25-71 years.

The differential diagnosis should include Laugier-Hunziker syndrome and Peutz-Jeghers syndrome. The absence of systemic features and involvement at other sites should assist in differentiating oral and labial melanotic macules from these syndromes. Both oral and labial melanotic macules are benign; however, lesions suggestive of malignancy should be examined at biopsy.

Vulvar and penile lentigo

Vulvar and penile lentigo are benign lesions similar to labial melanotic macules. In men, the most common sites are the glans penis, corona, corona sulcus, and penile shaft. The lesions vary in color from tan to brown to dark brown, and they have irregular borders and skip areas. Individual lesions may have a diameter as large as 15 mm. In women, the lesions appear anywhere on the genital mucosa as a mottled, pigmented patch with skip areas. The diameter can be 5-15 mm or larger. The lesions may also occur in episiotomy scars after childbirth. Lentigines involving the external genitalia are also reported in LAMB syndrome.

Lentigines profusa

Lentigines profusa (ie, generalized lentigines) is characterized by numerous lentigines without signs of associated abnormalities or triggering factors. The clinical appearance of lentigines profusa resembles that of ephelides, but its distribution is widespread. Usual areas of involvement include the extremities, trunk, palms, and genitalia. Mucosal surfaces such as the conjunctiva can also be affected, but the buccal mucosa may be spared. The macules vary from 1 mm to 2 cm in diameter. The color of the macules ranges from dark brown to black.

Lentigines profusa appears similar to the cutaneous manifestations of LEOPARD, LAMB, and NAME syndromes; however, a notable exception is the absence of the variety of the physical anomalies and defects associated with these syndromes.

Agminated lentiginosis

Agminated (segmental, unilateral, partial unilateral) lentiginosis is characterized by numerous lentigines confined to a body segment, with a sharp demarcation at the midline. The distribution frequently corresponds to one or more dermatomes. Less commonly, the lesions can be distributed unilaterally, bilaterally, in a checkerboard pattern, or in midline clusters. Usually, the disease appears in early childhood, although the lentigines may also be noted at birth. These lesions have been associated with numerous diseases. Clinically, the lesions appear as circumscribed, tan or dark brown macules on healthy background skin.

Xeroderma pigmentosum

Xeroderma pigmentosum (XP) is an autosomal-recessive condition involving abnormalities that stem from an inability of cells to repair DNA damage induced by exposure to UV light and certain chemicals. Clinically, patients have skin atrophy and progressive pigmentary changes. Subsequently, neoplastic changes occur on the skin, often in childhood; squamous cell and basal cell carcinomas are the most common malignancies. Other cancers, such as melanoma, may appear as well. All of these neoplastic changes evolve on sun-exposed areas, particularly the head, neck, and face.

XP is diagnosed in young children, who are typically healthy. Children should avoid sun exposure because the acceleration of skin changes leads to the formation of neoplasms. Ocular and neurologic defects are also associated with XP. See the image below.

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Thirteen-year-old Greek adolescent with xeroderma pigmentosum.

LEOPARD syndrome

LEOPARD syndrome (lentigines, electrocardiographic conduction defects, ocular hypertelorism, pulmonary stenosis, abnormal genitalia, retardation of growth, and deafness syndrome) (ie, multiple lentigines syndrome) is a complex dysmorphogenetic disorder that is transmitted as an autosomal-dominant trait with variable penetrance. A mutation of the PTPN11 gene may be documented.^[24] The diagnosis can be difficult because most patients have only 3-5 of the criteria. Lentigines are the most common feature of the syndrome, although they do not have to be present to diagnose LEOPARD syndrome.

In the absence of lentigines, the diagnosis can be made if the patient has 3 features of the disease and an immediate relative with the disease. Lentigines are present at birth and increase in number until puberty. The intensity of the pigmentation varies. The lesions are numerous on the neck and trunk, but they can also be widespread and involve the genitalia, palms, soles, and scalp. Lentigines spare some parts of the face and may be limited to one side of the body in some cases.

Peutz-Jeghers syndrome

Peutz-Jeghers syndrome is an autosomal-dominant condition with a high degree of penetrance and is characterized by gastrointestinal polyps and pigmented macules. The polyps are benign hamartomas that can affect the entire bowel, most characteristically the jejunum. These polyps result in recurrent perirectal bleeding and abdominal pain. Patients are often first seen with bleeding or with intussusception that manifests as an obstruction, abdominal pain, rectal prolapse, vomiting, and/or currant jelly–like stool.

Lentigines are brown-to-black-to-blue macules that usually arise in early childhood. Their size ranges from 1-12 mm in diameter. Hyperpigmented macules occur in more than 95% of patients, and they have a characteristic distribution around the mouth, on the lips, and on the buccal mucous membranes; they can also be scattered around the nose and face. Additionally, lesions appear on the fingers and toes on both the palmar and volar surfaces. Lesions are characteristically absent on the flexor and extensor surfaces of the rest of the body. The buccal mucosal macules are important because they persist, whereas the other macules may fade with age. A relationship between the extent of melanosis and the extent of polyposis has not been found.

Almost all women have unusual sex cord tumors that are small, bilateral, asymptomatic, and multifocal. Gonadal tumors are also noted in men. Women have an increased risk of breast cancer, either unilateral or bilateral in presentation.

Laugier-Hunziker syndrome

Laugier-Hunziker syndrome is characterized by a variable number of pigmented macules that most commonly appear on the lower lip; buccal mucosa; hard palate; and, occasionally, tips of the fingers. Other locations include the labial commissure, tongue, gums, floor of the mouth, neck, thorax, abdomen, nails, and soles. The lentigines may be numerous and confluent, but they rarely occur in a linear pattern. The lesions mostly occur on the nails. Their borders are smooth and well defined. The color of the lesions can vary from gray to brown, blue, or black. Although the syndrome has a chronic course without remission, individuals are generally asymptomatic.

This syndrome differs from Peutz-Jeghers syndrome because of the absence of intestinal polyps. Laugier-Hunziker syndrome occurs in individuals aged 20-50 years and in both sexes, whereas isolated labial melanotic macules affect younger patients and are usually solitary. Pigmentation of the oral mucosa and nails is reported to occur in patients taking the antiretroviral medication zidovudine. The clinical and drug histories are important in differentiating this phenomenon from Laugier-Hunziker disease.

Myxoma syndrome

The myxoma syndrome is associated with mucocutaneous lentigines along with various additional abnormalities. Some constellations of abnormalities have been given specific names. They may all be part of a spectrum of manifestations of the same disorder.

LAMB syndrome

LAMB (lentigines, atrial myxomas, mucocutaneous myxomas, and blue nevi) syndrome is one of the myxoma syndromes. The lentigines most commonly occur on the lips, face, sclera, and vulva. The lesions are brown and can be as large as 1 cm in diameter. The mucocutaneous myxomas appear as papules or dermal nodules at various sites on the body, including the breasts, shoulders, oral mucosa, and tongue. Cardiac myxomas are rare in children and usually occur in the form of atrial myxomas, which are clinically evident as intermittent embolic episodes and valvular obstructions. An association with benign thyroid nodules is noted.

NAME syndrome

NAME (nevi, atrial myxoma, myxoid neurofibroma, and ephelides) syndrome is another myxoma syndrome. This possible variant of LAMB syndrome involves multiple, flat, pigmented macules. The lesions begin at birth and are accentuated in the summer. The color of the lesions varies from pale to dark brown. The most commonly involved areas are the neck, trunk, and thighs. The palms and soles are sometimes affected.

Carney syndrome

Carney syndrome is an autosomal dominant multiple neoplasia syndrome involving cardiac, cutaneous, and mammary myxomatous masses; lentigines; blue nevi; endocrine disorders; and testicular tumors.^[25] Often, multicentric and bilateral organ involvement is present; this usually occurs in young patients. The cutaneous myxomas are often observed on the eyelids and other sites such as the nipples, scalp, face, oral mucosa, ears, neck, trunk, limbs, and perineum. Cardiac myxomas are either single or multiple and often result in fibrosis or calcification.

Two types of pigmented macules exist: blue nevi and lentigines. Lentigines are brown to black and 0.2-2 mm in diameter; they have irregularly shaped, jagged margins. They are widespread throughout the body and may coalesce to form brown patches. The lesions can be found on the face, eyelids, ears, vermilion borders of the lips, conjunctiva, vulva, extremities, and glans penis. Unlike Peutz-Jeghers syndrome, Carney syndrome infrequently involves buccal lesions. Endocrine involvement includes calcifying pigmented neuroectodermal tumors, pituitary adenomas with acromegaly and gigantism, and adrenocortical disease leading to Cushing syndrome.

Testicular tumors feature Sertoli cell tumors, Leydig cell tumors, and adrenocortical rest tumors. Mammary involvement includes gynecomastia and myxomatous enlargement of the stroma.

Inherited patterned lentiginosis

Inherited patterned lentiginosis can occur in blacks. This form is characterized by hyperpigmented macules on the face and lips. At times, additional lesions are seen on the elbows, knees, buttocks, and palmoplantar surfaces. Lesions are not present on the oral mucosa, and they are not associated with organ involvement or an apparent risk of cancer. The inheritance pattern appears to be autosomal dominant. Light-skinned African American families, some of whom have a mixed American Indian heritage and those with relatives with red hair, are particularly affected. See the image below.

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Ephelides (ie, freckles) on the forearm of a 26-year-old redheaded patient.

Nevus spilus

The nevus spilus is a both a lentigo and melanocytic nevus, a unique neoplasm that has only a slight potential to develop into melanoma.^[26] It is evident as multiple pigmented macules or papules within a congenital or acquired pigmented patch.

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Complications

Some lentigines have associated systemic manifestations that accompany the skin lesions (see Physical Examination).

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Other Tests

Dermoscopic evaluation of a few lichenoid regressing solar lentigines showed a pattern similar to that of lichenoid regressing seborrheic keratosis.^[32]

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Histologic Findings

Lentigo simplex is characterized by a slight-to-moderate elongation of the rete ridges with melanocyte proliferation in the basal layer, increased melanin in both the melanocytes and the basal keratinocytes, and the presence of melanophages in the upper dermis. Lentigines profusa and agminated lentigo are similar in appearance.

Solar lentigines have elongated rete ridges and a proliferation of pigmented basaloid cells, which form buds and strands. These rete ridges may appear flattened.^[33]  Ink-spot lentigines are also similar to solar lentigines, except the rete ridges in ink-spot lentigines appear less blunted and more tortuous. No atypia of the melanocytes is present. The solar lentigo has an increased number of melanophages compared with unaffected skin from the same subject.^[34] These melanophages were demonstrated to be factor XIIIa-positive dermal dendrocytes.

The melanocytes of PUVA lentigines are increased in number and hypertrophic; they frequently demonstrate cellular atypia. Elongation of the rete ridges and increased pigmentation in the basal cell region is present with transepidermal pigment cell excretion.

Radiation lentigines show increased melanin deposition in basal keratinocytes, cellular or nuclear atypia, increased number of melanocytes, and reduction of rete ridges.

Oral and labial melanotic macules show epithelial hyperplasia with somewhat irregular widening and elongation of the rete ridges. Melanin is increased in the melanocytes and keratinocytes of the basal layer and in the melanophages in the dermal papillae; this increase in melanin indicates pigment incontinence. Vulvar and penile lentigines have similar histologic features except for a slight increase in dendritic melanocytes along the basal layer of the epidermis.

Tanning-bed lentigines resemble PUVA lentigines with the increased density of melanocytes, some of which show mild nuclear atypia. Ultrastructurally, these lesions are similar to those of other forms of lentigo.

Ephelides have an increase in pigment content in the basal cell layer, with neither elongated rete ridges nor increased number of melanocytes.

The myxoma syndromes (ie, LAMB, NAME, and Carney syndromes) show basal layer and, sometimes, spinous layer hyperpigmentation with or without elongation of the rete ridges and melanocytic hyperplasia. Melanocytes may have large dendritic processes, and melanophages may be observed in the upper dermis.

In Peutz-Jeghers syndrome, the lentigines also show marked hyperpigmentation of the basal layer. LEOPARD syndrome involves increased pigment content of the epidermis with an increased number of melanocytes. The melanocytes are filled with melanosomes and are distributed singly or in the form of micronests.

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Medical Care

Noninvasive topical creams are also used. After several months of application, tretinoin cream and hydroquinone cream can lighten lentigines.

The efficacy and safety of cryotherapy and trichloroacetic acid (TCA) were compared for the treatment of solar lentigo.^[35] Cryotherapy was more effective than TCA 33% solution in the treatment of solar lentigines of the back of the hands, particularly in lighter-complexioned individuals. For darker-complexioned people, TCA 33% may be preferred, although postinflammatory hyperpigmentation remains a risk for both modalities.

A triple combination cream with fluocinolone acetonide 0.01%, hydroquinone 4%, and tretinoin 0.05% as adjuvant to cryotherapy for solar lentigines on the dorsal hands was found to be effective.^[36]

The effect of a bleaching solution containing 2% mequinol (4-hydroxyanisole, 4HA) and 0.01% tretinoin (Solagé) applied twice daily for 3 months on solar lentigines present on the back of one hand demonstrated a significant lightening effect after 2 months of treatment and was maintained at least 2 months after stopping treatment.^[37]

Skin-lightening products commercially available target natural melanin production, many as competitive inhibitors of tyrosinase.^[38]  Phalaenopsis orchid extract may be useful as a novel treatment of solar lentigines.^[39]

A weak but significant whitening effect on solar lentigos was documented using L-ascorbate-2-phosphate trisodium salt in Japanese women.^[40]

 Imiquimod 3.75% cream has been suggested as possibly efficacious.^[41]

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Surgical Care

Treatment of solar lentigines with a focal medium-depth chemical peel may be clinically superior to treatment with cryosurgery, owing to the paucity of adverse effects (eg, hypopigmentation, pain) associated with chemical peels.^[42]

Cryosurgery^[43] is a simple treatment for isolated lentigines. Many consider the first-line therapy for solar lentigines to be ablative therapy with cryotherapy.^[44] This procedure is often successful because of the susceptibility of melanocytes to freezing with liquid nitrogen. Squamous cells resist injury at -20°C, whereas melanocytes freeze at -4 to -7°C.

Lasers are effective in the treatment of various lentigines. The development of short-pulsed, pigment-specific lasers to selectively destroy the pigment within the solar lentigo has led to significant clinical improvement, a low risk of adverse effects, and high patient acceptance.^[45] The frequency-doubled, Q-switched Nd:YAG laser,^[46] the HGM K1 krypton laser, and the 532-nm diode-pumped vanadate laser are all used with success.^[47] Use of a low-fluence 1,064-nm Q-switched neodymium-doped yttrium aluminum garnet (QS Nd:YAG) laser is another choice.^[48]  

Treatment with Q-switched Nd:YAG laser may work better than fractional carbon dioxide laser for solar lentigines,^[49] with repetitive low-fluence 1064-nm Q-switched Nd:YAG laser being a safe and effective approach for them.^[50]

Intense pulsed-light (IPL) treatment is another option.^[51]

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Prevention

The application of sunscreen helps decrease the rate of appearance and the darkening of solar lentigines. Summer darkening can be avoided by use a SPF-30 day skin cream.^[52] Limiting one's exposure to sun tanning and the use of artificial sources of UV light may help prevent solar lentigines.

Limiting one's exposure to sun tanning and the use of artificial sources of UV light may help prevent solar lentigines.

Individuals of Celtic ancestry might limit their exposure to the sun to help prevent ink-spot lentigines.

The avoidance of a large single dose of ionizing radiation may prevent radiation lentigines.

Children with XP should avoid sun exposure because the acceleration of skin changes leads to the formation of neoplasms.

The avoidance of the intense or prolonged, regular use of tanning beds may help in preventing tanning-bed lentigines.

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Medication Summary

The goal of pharmacotherapy is to reduce morbidity and prevent complications.

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Tretinoin 0.025 to 0.1% (Retin-A, Avita)

• Dosing, Interactions, etc.

Clinical Context:  Tretinoin is a keratolytic agent. It acts by increasing epidermal cell mitosis and turnover while suppressing keratin synthesis. An important side effect of interest is hypopigmentation, which reduces the appearance of lentigines.

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Class Summary

Retinoids decrease the cohesiveness of abnormal hyperproliferative keratinocytes and may reduce the potential for malignant degeneration. These agents modulate keratinocyte differentiation. They have been shown to reduce the risk of skin cancer in patients who have undergone renal transplantation.

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Hydroquinone (Eldopaque-Forte, Solaquin Forte, Lustra)

• Dosing, Interactions, etc.

Clinical Context:  Hydroquinone suppresses melanocyte metabolic processes, especially enzymatic oxidation of tyrosine to 3,4-dihydroxyphenylamine. Exposure to sun reverses the effects and causes repigmentation.

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Class Summary

These agents lighten hyperpigmented skin by inhibiting enzymatic oxidation of tyrosine and by suppressing other melanocyte metabolic processes, thereby further inhibiting melanin production.

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