Actinic Keratosis



Actinic Keratosis


David Cassarino, MD, PhD





Key Facts


Terminology



  • Actinic keratosis (AK)


  • Solar keratosis


  • Atypical intraepidermal proliferation of keratinocytes typically confined to basilar portion of epidermis


Clinical Issues



  • Older adults typically affected


  • Mostly occur in Caucasians, much less common in other races


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


Microscopic Pathology



  • Basilar budding of atypical cells


  • Cells show nuclear enlargement, hyperchromasia, and prominent nucleoli


  • Overlying parakeratosis present


  • Lesional cells usually do not involve follicles (as opposed to Bowen disease)


  • Histologic subtypes include hypertrophic, atrophic, pigmented, lichenoid, and bowenoid AK


Top Differential Diagnoses



  • Squamous cell carcinoma (SCC)


  • Bowen disease (SCC in situ)


  • Basal cell carcinoma (BCC), superficial-multicentric and basosquamous types


  • Melanoma in situ (lentigo maligna type)


  • Discoid lupus erythematosus


  • Lichen planus (LP) and lichen planus-like keratosis (benign lichenoid keratosis [BLK])







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






Low-magnification view of an actinic keratosis shows basilar keratinocytic budding and atypia image, with sparing of a central hair follicle. Prominent overlying parakeratosis image is typically present.


TERMINOLOGY


Abbreviations



  • Actinic keratosis (AK)


Synonyms



  • Solar keratosis


  • Often considered a “precancer” or early squamous cell carcinoma in situ (SCCis)


Definitions



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


ETIOLOGY/PATHOGENESIS


Solar Damage



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


  • P53 mutations are most common genetic alteration identified


CLINICAL ISSUES


Epidemiology



  • Incidence



    • 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



    • Older adults typically affected


  • Gender



    • Males more common than females


  • Ethnicity



    • Mostly occur 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 squamous cell carcinoma


Treatment



  • Options, risks, complications



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


  • Surgical approaches



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


  • Drugs



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


    • Liquid nitrogen (cryotherapy) frequently used


    • Photodynamic therapy is also an emerging treatment that may be useful for extensive AKs


Prognosis



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


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



MACROSCOPIC FEATURES


Size



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


MICROSCOPIC PATHOLOGY


Histologic Features

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Jul 8, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Actinic Keratosis

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