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.)

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.

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.

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.



• Actinic keratosis (AK)


• Solar keratosis

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


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


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



• 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


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


• Scaly papules and plaques, often multiple

Natural History

• Minority of cases progress to invasive SCC


• 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


• 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



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


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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