Actinic Keratoses

Clinical and Pathological Features

Pathogenesis and Genetic Mutations

• UV damage: UVB (290–320 nm) and UVA (320–400 nm) radiation damage DNA directly, creating abnormal pyrimidine dimers (thymine dimers) in keratinocytes.
• TP53 mutations: Mutation of the tumor suppressor gene TP53 is the key first event. Keratinocytes with damaged DNA can no longer undergo programmed cell death (apoptosis), so they multiply abnormally and pick up further mutations (NOTCH1, CDKN2A).

Clinical Variants

AKs usually appear on chronically sun-exposed skin (face, bald scalp, forearms, backs of the hands, back of the neck):

• Classic (erythematous) AK: Pink-red papules or plaques with a rough surface and firmly stuck-on scale. They are often easier to feel (like sandpaper) than to see.
• Hyperkeratotic AK / cutaneous horn: Thick keratin builds up and projects from the skin as a spur or small horn. These need careful attention, because the base of a cutaneous horn can easily hide an invasive squamous cell carcinoma.
• Pigmented AK: Rough brown-black patches that are easily mistaken for solar lentigo, seborrheic keratosis or melanoma in situ (lentigo maligna).
• Actinic cheilitis: The AK variant on the lower lip. The lip is dry, the border between lip and skin becomes blurred, and there is persistent white scale with cracks that bleed easily.

Histopathology

• Keratinocyte atypia: Keratinocytes in the basal and lower spinous layers have large, irregular, hyperchromatic nuclei, lose their polarity and show increased mitotic activity.
• Parakeratosis and the flag sign: Parakeratosis (retained nuclei) over the abnormal epidermis alternates with orthokeratosis over the intact follicular and sweat duct openings, producing the "flag sign".
• Sparing of the acrosyringium and acrotrichium: Atypical keratinocytes surround the follicular infundibulum and sweat ducts but do not invade them.
• Solar elastosis: In the upper dermis, UV-damaged collagen fibers break up and are replaced by pale blue-gray staining bands.

Differential Diagnosis and Immunohistochemistry (IHC)

Our Approach to Treating Actinic Keratoses

Haute-Derma builds its AK treatment plans around prevention and management of the whole affected area:

• Field cancerization management: Rather than destroying individual AKs only, we treat the whole surrounding area of sun-damaged skin to clear microscopic disease that has not yet surfaced.
• Screening for invasion: Thick AKs, lesions with a firm, infiltrated base, and those that ulcerate or bleed are assessed carefully so we can switch promptly to treatment for invasive squamous cell carcinoma if needed.
• Combining lesion-directed and field-directed therapy: We pair techniques that destroy individual lesions with topical or photodynamic treatments of the wider area for the best clinical and cosmetic results.

How We Diagnose Actinic Keratoses at Haute-Derma

To diagnose AK accurately without missing an invasive skin cancer, Haute-Derma follows a four-step process:

• Clinical examination and high-resolution dermoscopy: We look for the characteristic strawberry pattern: a red pseudonetwork interrupted by follicular openings ringed with white-yellow halos, along with rosettes.
• Grading the lesions (Olsen grading):
  • Grade I (mild): Flat, slightly rough patches that are easier to feel than to see.
  • Grade II (moderate): Rough pink-red papules with clearly visible scale.
  • Grade III (severe): Thick, hard hyperkeratotic plaques with heavy, rough scale or a cutaneous horn.
• Skin biopsy (shave or punch): Required for grade III lesions, lesions that are notably painful or tender, those with a firm infiltrated base, or those that do not respond to initial treatment.
• Assessing and mapping the field: We define the boundaries of the wider sun-damaged area so we can choose the right field treatment.

How We Treat Actinic Keratoses at Haute-Derma

Treatment is tailored to the number of lesions, how thick they are and the size of the affected field:

• Lesion-directed therapies (for individual AKs):
  • Liquid nitrogen cryotherapy: Liquid nitrogen spray freezes the lesion for 5–10 seconds. This is the gold standard for quickly treating isolated grade I and II AKs.
  • Ultrapulsed micro-spot CO2 laser or curettage: Precisely vaporizes thick AKs or cutaneous horns (grade III) without deep damage to the surrounding healthy skin.
• Field-directed therapies (for multiple AKs and damaged skin):
  • Topical chemotherapy (5-fluorouracil, 5-FU 5% or 0.5%): Blocks DNA synthesis and selectively destroys genetically altered keratinocytes. It is applied 1–2 times a day for 2–4 weeks and produces a local inflammatory reaction that clears the abnormal cells.
  • Topical immune modulator (imiquimod 3.75% or 5%): Stimulates the skin's immune system to produce interferon-alpha, which helps the body clear abnormal cells itself.
  • Photodynamic therapy (PDT): A light-sensitizing agent (5-ALA or MAL) is applied to the affected skin for 3 hours, followed by a dedicated red light source (630 nm). The photochemical reaction generates reactive oxygen species that selectively destroy AK cells over a wide area and rarely leave scars.
  • Tirbanibulin 1% ointment: A new-generation microtubule inhibitor applied once daily for just 5 consecutive days. It clears AKs effectively and the local reaction is usually mild.