actinic elastosis

WKP

Definition: Actinic elastosis, or solar elastosis, is an accumulation of abnormal elastin (elastic tissue) in the dermis of the skin, and in the conjunctiva of the eye, which occurs as a result of the cumulative effects of prolonged and excessive sun exposure, a process known as photoaging.

Microscopy

In the earlier stages of actinic elastosis, elastic fiber proliferation can be seen in the dermis.

As the condition becomes more established, the collagen fibers of the papillary dermis and reticular dermis become increasingly replaced by thickened and curled fibers that form tangled masses and appear basophilic under routine haematoxylin and eosin staining.

These fibers stain black with the Verhoeff stain.

Diagnostic biopsy is undertaken in only a small percentage of actinic keratoses diagnosed clinically. The clinical accuracy in the recognition of actinic keratoses varies from 74 to 94%.

The usual actinic keratosis is characterized by focal parakeratosis, with loss of the underlying granular layer and a slightly thickened epidermis with some irregular downward buds.

Uncommonly, the epidermis is thinner than normal.

In all cases there is variable loss of the normal orderly stratified arrangement of the epidermis; this is associated with cytological atypia of keratinocytes, which varies from slight to extreme.

The term ‘bowenoid actinic keratosis’ may be used when the atypia is close to full thickness. This variant differs markedly from the ‘de novo’ form of Bowen’s disease.

Sometimes the dysplastic epithelium shows suprabasal cleft formation.

There is often a sharp slanting border between the normal epidermis of the acrotrichia and acrosyringia and the parakeratotic atypical epithelium of the keratosis. However, dysplastic epithelium may involve the infundibular portion of the hair follicle.

The parakeratotic scale may sometimes pile up to form a cutaneous horn.

Large keratohyaline granules are sometimes present in actinic keratoses.

The dermal changes include actinic elastosis, which is usually quite severe, and a variable, but usually mild, chronic inflammatory cell infiltrate.

As mentioned above, the grade of solar elastosis is a marker of epithelial UV damage.

Inflammatory keratoses may develop during chemotherapy of malignant disease with fluorouracil and its analogues.

There is vascular telangiectasia and a moderately heavy mixed inflammatory cell infiltrate in the upper dermis. Inflammation of actinic keratoses has also been reported following therapy with sorafenib, a multitargeted tyrosine-kinase inhibitor.

Some actinic keratoses progress to squamous cell carcinoma with this therapy.

An inflammatory response is also present in actinic keratoses before they progress to squamous cell carcinomas, unrelated to any therapies. The inflammation subsides rapidly following this conversion.

In all types of actinic keratoses in immunosuppressed patients there is usually marked atypia of the keratinocytes; multinucleate forms may be present. Confluent parakeratosis and verruciform changes may also occur.

Variants

 hyperplastic actinic keratosis (hypertrophic actinic keratosis)
 proliferative actinic keratosis
 atrophic actinic keratosis
 acantholytic actinic keratosis
 pigmented actinic keratosis
 bowenoid actinic keratosis
 lichenoid actinic keratosis
 lymphomatoid actinic keratosis

Electron microscopy

Ultrastructural studies suggest that the hyperpigmentation in the pigmented variant is due to enhanced melanosome formation and distribution, and not to a block in the transfer of melanosomes to keratinocytes.

Differential diagnosis

 epidermal dysmaturation following chemotherapy or transplantation.

• Actinic keratoses must be distinguished from the epidermal dysmaturation that may be seen following chemotherapy or transplantation.
• It is a histological diagnosis characterized by disruption of keratinocyte maturation, loss of polarity, widened intercellular spaces, irregular large nuclei, mid-epidermal mitotic figures, and apoptosis.
• Colchicine intoxication can also result in dysmaturation with metaphase-arrested keratinocytes and basal vacuolar change.

 carcinoma

• It is sometimes a matter of personal judgment whether a lesion is considered to show early squamous cell carcinomatous change or not.
• The protrusion of atypical cells into the reticular dermis and the detachment of individual nests of keratinocytes from the lower layers of the epidermis are criteria used to diagnose invasive transformation.
• Step sections are important in small biopsies initially regarded as solar keratosis. More significant pathology may emerge in the deeper sections.
• Despite these difficulties there is a good concordance in the diagnosis of these borderline cases among dermatopathologists.
• An AgNOR analysis may identify actinic keratoses with high proliferative activity and an increased tendency to develop into invasive squamous cell carcinoma.

See also

 actinic keratosis