Dyspigmentation of aged skin

ARTICLE

The clinical features of photoaged skin are somewhat different from those due to chronological aging. In the epidermis, melanin pigment is a good indicator of the photodamage and pigmentary changes are one of the most visible markers of photoaged skin.

According to the Glogau photoaging classification, in type I corresponding to early photoaging, mid-pigmentary changes are present. Glogau II photoaging is characterized by the visibility of early actinic lentigines. In Glogau III i.e., advanced photoaging, the skin dyschromia is obvious.

Exposed skin of the elderly is usually unevenly pigmented with a mottled appearance, demonstrating that chronic sun-exposure to UV-radiations may severely damage the melanocyte system of the skin, resulting in both hyper and hypomelanotic lesions. The mottled, irregular areas of pigmentation of photoaged skin may be explained by the increased dopa-positivity of melanocytes in the chronically sun-exposed skin and by an irregular distribution of melanosomes within epidermal keratinocytes.

Dyspigmentation of chronological aging

The number of dopa-positive melanocytes in human skin decreases with age. A decrease by approximately 10-20% with each decade is observed in both habitually sun-exposed and protected areas. Melanocyte density, however, is approximately twofold higher in chronically sun-exposed skin than in protected skin at all ages. This observation suggests that the principal effect of chronic sun-exposure on human melanocytes is not premature aging, but activation and/or proliferation of the exposed melanocytes.

Age related changes in the number of melanocytic naevi (MN) are also a feature of aging. The life cycle of MN is as follows: a growth phase during which sun-exposure may play a stimulating role from birth to young adulthood followed by a long period of quiescence and eventually involution.

Greying and whitening of hair is the physical trait most closely correlating with chronological age of all physiological functions. Most investigators agree that the number of melanocytes in grey or white hair is greatly reduced. The mechanism underlying this decrease of pigment cells has not yet been established.

Hypomelanotic lesions

The most common hypomelanotic disorder of photoaged skin is idiopathic guttate hypomelanosis. This disorder is characterized by multiple small pure white macules distributed on the sun-exposed surfaces of the forearms and the legs, usually in association with other skin changes of chronological aging and photodamage. The denominations of solar leukoderma or actinic punctate leukoderma have been proposed for this disorder. The most consistent histopathological features of the white macules are a flattening of the dermal-epidermal junction, moderate to relatively marked reduction in the number of dopa-positive melanocytes. Several arguments suggest that this disorder results at least partly from chronic natural UV-light exposure (occurrence on the most sun-exposed areas on female patients with a history of chronic sun-exposure, IGH-like lesions described in PUVA treated patients).

Spontaneous stellate pseudo scars are very common in elderly individuals. They appear as small white spots with a stellate shape, usually located on the back of the hands or on the extensor aspects of the forearms. The whitish appearance of these lesions suggest a defect in the melanocyte system of the skin. Specific melanin stain suggests that the white colour is not due to a melaconyte defect, but rather to dermal abnormalities. However no specific histochemical or ultrastructural study of the melaconytes has yet been performed. The pathogenesis of the disorder, clearly related to aging, is unknown. The topography of the lesions suggests a predisposing role for chronic sun-exposure. The role of repeated microtrauma has been suggested.

Hypermelanotic lesions

Actinic or solar lentigo (AL) is the most common hypermelanotic lesion of photoaged skin. They occur as multiple lesions in areas of skin chronically exposed to the sun. The most prominent histological features of AL include hyperpigmentation of the basal cell layer with a marked increase in the number of epidermal dopa-positive melanocytes and elongations of the rete ridges. AL may be extremely difficult to distinguish from the other pigmented lesions present on the skin of almost all elderly patients, including flat pigmented seborrheic keratoses, flat pigmented actinic keratoses, ephelides and naevocellular naevi. UV-A and PUVA lentigines are histologically very similar to AL.

Ephelides appear in childhood and increase in number in adults. Clinical evidence indicates that fair skin, red or light hair colour, light eye-colour and freckles are phenotype markers of increased susceptibility to sun-induced skin damage. Sequence variants of the melanocyte-stimulating hormone respecter gene MCIR are associated with this "phaeomelanic" phenotype. Pigmented actinic keratoses (PAK) may be slightly scaly and verrucous on a crythematous background. Histologically, these lesions show varying degrees of hyperkeratosis, acanthosis and finger-like projections and budding of atypical keratinocytes in the lower epidermis. In addition, there is an increased amount of melanization in the epidermal basal layer and numerous melanophages in the upper dermis. The possibility that these lesions represent a distinct clinicopathological entity with a marked progressive lateral spread has been raised and the term spreading pigmented AK (SPAK) was introduced. Hyperpigmented seborrheic keratoses (HSK) are more common with age. However, epidemiological data suggest that exposure to sunlight is a risk factor for SK. Other common pigmented lesions in sun exposed skin of elderly people include pigmented epitheliomas and lentigo melanoma.

Poikiloderma of Civatte and crythrosis interfollicularis Colli are two clinical phenotypes corresponding to a single entity representing one of the skin manifestations of skin aging. They are characterized by telangiectasia, pigmentation of the upper chest and lateral neck but sparing the submental area.

Treatment

Medical treatment of dyspigmentation of photoaged skin includes topical tretinoin and depigmenting agents, and to a lesser extent alpha-hydroxy-acids. Surgical procedures such as liquid nitrogen cryotherapy, chemexfoliation with trichloroacetic acid, phenol or alpha-hydroxy-acids, dermabrasion, laser for pigmented lesions and laser surfacing and surgical ablation with the recently developed pigment-specific lasers are also widely used. Last but not least, prevention should begin in early childhood and extend throughout life (limitation of mid day sun exposure, UVA and UVB sunscreens, photoprotective clothing...).

Reference

Ortonne JP, Marks R. Photodamaged skin. Clinical signs, causes and management. Martin Dunitz, 1999: 29-60.