Actinic Keratosis


Clinical Photograph of Actinic Keratosis
Clinical photograph of the scalp of an elderly patient shows multiple actinic keratoses (AKs) with prominent crusting. (Courtesy J. Wu, MD.)



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Bowenoid Actinic Keratosis
Bowenoid AK shows basilar to midepidermal involvement by atypical cells image, with a mitotic figure image. Overlying hyperkeratosis and parakeratosis are also present.

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Classic Actinic Keratosis With Overlying Parakeratosis
Low-magnification view of an AK shows basilar keratinocytic budding and atypia image, with sparing of a central hair follicle. Areas of prominent overlying parakeratosis image are also present.

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Actinic Keratosis at High Magnification
Another AK involving the superficial portion of a hair follicle shows basilar keratinocytic budding and atypia image, with a mitotic figure image. Parakeratosis is also present image within and overlying the follicle.


TERMINOLOGY


Abbreviations




• Actinic keratosis (AK)


Synonyms




• Solar keratosis

• Often considered precancer or form of early squamous cell carcinoma (SCC) in situ


Definitions




• Atypical intraepidermal proliferation of keratinocytes typically confined to basilar portion of epidermis, with very low risk for progression to invasive SCC


ETIOLOGY/PATHOGENESIS


Solar Damage




• Ultraviolet light (primarily UVB) induces mutations in DNA, which leads to abnormal proliferation of intraepidermal keratinocytes

• TP53 mutations are most common genetic alteration identified


CLINICAL ISSUES


Epidemiology




• Incidence
image Very common lesions, estimated to affect up to 10-40% of adult Caucasians; higher incidence in areas with heavy sun exposure (i.e., Australia)

• Age
image Older adults typically affected

• Sex
image Males more common than females

• Ethnicity
image Mostly occurs in Caucasians; much less common in other races


Site




• Sun-exposed sites, especially face, head and neck, dorsal hands, and forearms


Presentation




• Scaly papules and plaques, often multiple


Natural History




• Minority of cases progress to invasive SCC


Treatment




• Options, risks, complications
image Controversial whether treatment is necessary in all cases, but most clinicians opt for treatment to avoid potential development of SCC

• Surgical approaches
image Conservative excision of lesions is not necessary in most cases (unless there is clinical suspicion for invasive SCC) but is curative

• Drugs
image Topical therapy with drugs such as 5-fluorouracil, diclofenac, or imiquimod may be used

image Liquid nitrogen (cryotherapy) frequently used

image Photodynamic therapy is also emerging treatment that may be useful for extensive AK


Prognosis




• Excellent in vast majority of cases, as only ~ 2-3% progress to invasive SCC

• Most invasive SCCs arising in AK are low grade, but aggressive cases may also occur


MACROSCOPIC


Size




• Usually small (< 1 cm) papules, but larger lesions may occur


MICROSCOPIC


Histologic Features




• Intraepidermal proliferation of atypical keratinocytes, typically confined to basilar 1/3 of epithelium
image Basilar budding of atypical cells

image Cells show nuclear enlargement, hyperchromasia, and prominent nucleoli

image Abundant eosinophilic-staining cytoplasm

image Increased numbers of mitotic figures usually present

• Overlying parakeratosis present in vast majority of cases; hypogranulosis may also be present

• Lesional cells usually do not involve follicles (as opposed to Bowen disease) and adnexal ducts
image Leads to alternating red and blue tiers of parakeratosis (overlying AK) and hyper/orthokeratosis (overlying follicles and eccrine ducts)

• Histologic subtypes
image Hypertrophic AK
– Shows epidermal hyperplasia, often psoriasiform, with prominent overlying hyperkeratosis and parakeratosis

– Dermal fibrosis and vertical collagen bundles often present, suggesting lichen simplex chronicus changes (due to chronic excoriation) superimposed on AK

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Apr 24, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Actinic Keratosis

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