Actinic keratosis is a scaly spot found on sun-damaged skin, and can also be known as solar keratosis or sunspots.
It is considered pre-malignant skin cancer, an early form of cutaneous squamous cell carcinoma.

Actinic keratoses affect people that have the following risk factors:

  • signs of photo-aging skin
  • Fair skin with a history of sunburn
  • History of long hours spent outdoors for work or recreation
  • Defective immune system

Actinic keratoses are a reflection of abnormal skin cell development due to DNA damage by short wavelength UVB.
They are more likely to appear if the immune function is poor, due to aging, recent sun exposure, predisposing disease or certain drugs.

Clinical Features

Actinic keratosis may be solitary but there are often multiple keratoses. The appearance varies.

  • A flat or thickened papule or plaque
  • White or yellow; scaly, warty or horny surface
  • Skin coloured, red or pigmented
  • Tender or asymptomatic

Actinic keratoses are very common on sites repeatedly exposed to the sun, especially the backs of the hands and the face, most often affecting the ears, nose, cheeks, upper lip, vermilion of the lower lip, temples, forehead and balding scalp. In severely chronically sun-damaged individuals, they may also be found on the upper trunk, upper and lower limbs, and dorsum of feet.

The main concern is that actinic keratoses predispose to squamous cell carcinoma.

Treatment

Actinic keratoses are usually removed because they are unsightly or uncomfortable, or because of the risk that skin cancer may develop in them.
Treatment of an actinic keratosis requires removal of the defective skin cells. Epidermis regenerates from surrounding or follicular keratinocytes that have escaped sun damage.
Tender, thickened, ulcerated or enlarging actinic keratoses should be treated aggressively. Asymptomatic flat keratoses may not require active treatment but should be kept under observation.

Cryotherapy using liquid nitrogen
Liquid nitrogen is required to ensure adequate depth and duration of the freeze. This varies according to lesion location, width, and thickness. Healing varies from 5–10 days on the face, 3–4 weeks on the hands, and 6 weeks or longer on the legs. A light freeze for a superficial actinic keratosis usually leaves no mark, but longer freeze times result in hypopigmentation or scar.

Shave, curettage and electrocautery
Shave, curettage (scraping with a sharp instrument) and electrocautery (burning) may be necessary to remove a cutaneous horn or hypertrophic actinic keratosis. Healing of the wound takes several weeks or longer, depending on where it is located on the body. A specimen is sent for pathological examination.

Excision
Excision ensures the actinic keratosis has been completely removed, which should be confirmed by pathology. The surgical wound is sutured (stitched). The sutures are removed after a few days, the time depending on the size and location of the lesion. The procedure leaves a permanent scar.

Field Treatments

Creams are used to treat areas of sun damage and flat actinic keratoses, sometimes after physical treatments have been carried out. Field treatments are most effective on facial skin. Pretreatment with keratolytics (such as urea cream, salicylic acid ointment or topical retinoid), and thorough skin cleansing improves response rates. Results are variable and the course of treatment may need repeating from time to time. With the exception of diclofenac gel, field treatments all result in local inflammatory reactions such as redness, blistering, and discomfort for a varying length of time.

  • Diclofenac is more often used as an anti-inflammatory drug. Applied as a gel twice daily for 3 months, it is fairly well tolerated in the treatment of actinic keratoses, but less effective than the other options listed here.
  • 5-Fluorouracil is a cytotoxic agent. The cream formulation is applied once or twice daily for 2 to 8 weeks. 5-fluorouracil cream is sometimes combined with salicylic acid. Its effect may be enhanced by calcipotriol ointment.
  • Imiquimod cream is an immune response modifier. It is applied 2 or 3 times weekly for 4 to 16 weeks.
  • Photodynamic therapy (PDT) involves applying a photosensitiser (a porphyrin chemical such as methyl aminolevulinic acid) to the affected area prior to exposing it to a source of visible light.
  • Ingenol mebutate gel is effective after only 2–3 applications.
Prevention

Actinic keratoses are prevented by strict sun protection. If already present, keratoses may improve with very high sun protection factor (50+) broad-spectrum sunscreen applied at least daily to affected areas, year-round.
The number and severity of actinic keratoses can also be reduced by taking nicotinamide (vitamin B3) 500 mg twice daily.

Prognosis

Actinic keratoses may recur months or years after treatment. The same treatment can be repeated or another method used. Patients who have been treated for actinic keratoses are at risk of developing new spots, they are also at increased risk of other skin cancers, especially; intraepidermal squamous cell carcinoma, invasive cutaneous squamous cell carcinomabasal cell carcinoma, and melanoma.

References:

  1. https://www.dermnetnz.org/
  2. Clinical Dermatology by Thomas Habif
  3. https://www.betterhealth.vic.gov.au/