Actinic keratosis

Actinic keratosis
Diagnosis in short
LM	basal epidermal atypia - key feature, palisading of basal cells, solar elastosis +/-parakeratosis
Subtypes	bowenoid actinic keratosis, hypertrophic actinic keratosis, acantholytic actinic keratosis, proliferative actinic keratosis, pigmented actinic keratosis, lichenoid actinic keratosis
LM DDx	squamous cell carcinoma of the skin, Bowen's disease
IHC	CK34betaE12 +ve
Site	skin
Associated Dx	squamous cell carcinoma of the skin, Bowen's disease
Signs	sandpaper-like texture
Prognosis	good
Clin. DDx	squamous cell carcinoma, melanoma (for pigmented AK)

Actinic keratosis, abbreviated AK, is a common skin lesion. It is also known as solar keratosis.

General

• Considered a precursor of squamous cell carcinoma of the skin.

Risk factors:

• Sun exposure.
• Immune suppression (e.g. organ transplant recipients).

Gross

Features:

• Yellow-brown scaly, patches.
• Sandpaper sensation - on touching.
• Usually small (<1cm), but larger lesions may occur.
• May be pigmented.

Microscopic

Features:

• Epidermal nuclear atypia:
  • Variation is size, shape and staining - must involve basilar layer.
    • Nuclear enlargement - key feature.
    • Hyperchromasia.
• Abnormal epidermal architecture:
  • Palisading.^{[citation needed]}
• +/-Parakeratosis - may alternate with orthokeratosis, esp. early lesions.
• +/-Irregular acanthosis.

Note:

• May be full thickness - known as bowenoid actinic keratosis.

DDx:

• Actinic cheilitis - the same lesion on the lip.
• Bowen's disease - full thickness involvement - with involvement of adnexal epithelium and follicular epithelium.
• Paget disease of the breast.
• Squamous cell carcinoma of the skin.
• Lentigo maligna (melanoma in situ on sun damaged skin) - esp. for pigmented AK.
  • One should see benign melanocytes within an AK... otherwise one should do stains as the melanocytes may be mimicking keratinocytes.
• Seborrheic keratosis - should not have basilar nuclear atypia.
• Lichenoid keratosis (esp. for lichenoid actinic keratosis) - has a band of inflammatory cells in the superficial dermis.
• Discoid Luphus Erythematosus.

Images

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  Actinic keratosis. (WC)

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  Actinic keratosis. (WC)

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  Actinic keartosis. (WC)

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  Actinic keratosis. (WC)

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  Bowenoid actinic keratosis - high mag. (WC)

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  Bowenoid actinic keratosis - very high mag. (WC)

Histologic subtypes of actinic keratosis

Like most common things, there are several variants:

• Hypertrophic actinic keratosis.
  • Increased thickness of: (1) epidermis and, (2) stratum corneum.
• Acantholytic actinic keratosis.
• Proliferative actinic keratosis - downward finger-like projections of the epidermis.
• Pigmented actinic keratosis.
  • DDx: lentigo maligna.
• Lichenoid actinic keratosis - band of inflammatory cells at the dermal-epidermal junction.
  • DDx: lichen planus.
• Atrophic actinic keratosis.

Sign out

Left Ear Skin Lesion, Biopsy:
	- Hypertrophic squamous lesion, possibly hypertrophic actinic keratosis, see comment.
	- Solar elastosis, marked.

Comment:
The lesion has mild basal atypia, proliferative activity and marked hyperkeratosis. The lesion extends to the edge of the tissue and may not be representative of the lesion seen clinically.  Clinical correlation is required. Re-excision to rule-out un-sampled pathology should be considered.

All uppercase

SKIN LESION, RIGHT THIGH, BIOPSY:
- HYPERTROPHIC ACTINIC KERATOSIS.
- SOLAR ELASTOSIS.
- NEGATIVE FOR MALIGNANCY.

Bowenoid

SKIN LESION, RIGHT DISTAL FOREARM, BIOPSY:
- BOWENOID ACTINIC KERATOSIS, COMPLETELY EXCISED IN PLANE OF SECTION.
- EXTENSIVE SOLAR ELASTOSIS.
- NEGATIVE FOR MALIGNANCY.

Micro

General

The sections show skin with basilar epidermal nuclear enlargement and hyperchromasia with irregular nuclear palisading. Hyperkeratosis and parakeratosis is present. A granular layer is present. The dermal-epidermal interface is sharply-demarcated. There is focal inflammation at the interface. Extensive solar elastosis is present.

There is no clefting of the lesion from the surrounding stroma. The surrounding stroma does not have a myxoid quality.

Bowenoid

The sections show skin with epidermal nuclear enlargement and hyperchromasia with irregular nuclear palisading. The lesion involves the full thickness of the epidermis; however, it spares adnexal and follicular epithelium. Proliferative activity is present. Hyperkeratosis and parakeratosis is present. A granular layer is present. The dermal-epidermal interface is sharply-demarcated. There is focal inflammation at the interface. Extensive solar elastosis is present.

There is no clefting of the lesion from the surrounding stroma. Intercellular bridges are identified.

Lichenoid AK

The sections show skin with a lymphoplasmacytic interface dermatitis, hypergranulosis, hyperkeratosis, loss of the rete ridges and apoptotic keratinocytes. The epidermis matures to the surface; however, there is basal cell hyperplasia associated with moderate keratinocyte nuclear atypia (including hyperchromasia and anisonucleosis). Pigment incontinence is present. Solar elastosis is present. The lesion is completely excised in the plane of section.

See also

• Non-malignant skin disease.
• Dermatopathology.
• Squamous cell carcinoma of the skin.