Actinic keratosis is a premalignant condition of thick, scaly, or crusty patches of skin.
It is more common in fair-skinned people and it is associated with those who are frequently
exposed to the sun, as it is usually accompanied by solar damage.
They are considered as potentially pre-cancerous, since some of them progress to squamous cell
carcinoma, so treatment is recommended.
Untreated lesions have up to 20% risk of progression to squamous cell carcinoma.
Progressive development of these lesions occurs when skin is exposed to the sun constantly
and thick, scaly, or crusty areas appear.
The scaly or crusty portion is dry and rough.
The lesions start out as flat scaly areas and later grow into a tough, wart-like area.
An actinic keratosis site commonly ranges between 2 and 6 millimetres in size, and may
be dark or light, tan, pink, red, a combination of all these, or have the same pigment as
the surrounding skin.
The lesion may appear on any sun-exposed area, such as the face, ears, neck, scalp, chest,
backs of hands, forearms, or lips.
Classification
Actinic keratoses may be divided into the following types:
Hyperkeratotic actinic keratosis Pigmented actinic keratosis
Lichenoid actinic keratosis Atrophic actinic keratosis
See also: Actinic cheilitis
Cutaneous horn Squamous cell carcinoma in situ
Diagnosis Physicians can usually identify actinic keratosis
by doing a thorough examination; in principle actinic keratosis is a clinical diagnosis.
A biopsy may be necessary when the keratosis is large or thick, to make sure that the lesion
is a keratosis and not a skin cancer.
Seborrheic keratoses are other lesions that appear in groups as the actinic keratosis
do, but are not caused by sun exposure, and are not related to skin cancers.
Seborrheic keratoses may be mistaken for an actinic keratosis.
Specialized forms of actinic keratoses include cutaneous horns, in which the skin protrudes
in a thick, hornlike manner, and actinic cheilitis, a scaling and roughness of the lower lip and
blurring of the border of the lip and adjacent skin.
Histopathology Actinic keratosis usually shows focal parakeratosis
with associated loss of the granular layer of, and thickening of the epidermis.
The normal ordered maturation of the keratinocytes is disordered to varying degrees, there may
be widening of the intracellular spaces, and they may also have some cytologic atypia,
such as abnormally large nuclei.
The underlying dermis often shows severe actinic elastosis and a mild chronic inflammatory
infiltrate.
Prevention Preventive measures recommended for actinic
keratosis are similar to those for skin cancer: Not staying in the sun for long periods of
time without protection Frequently applying powerful sunscreens with
SPF ratings greater than 30 and that also block both UVA and UVB light
Wearing sun protective clothing such as hats, long-sleeved shirts, long skirts, or trousers
Avoiding sun exposure during noon hours is very helpful because ultraviolet light is
the most powerful at that time According to an article in the Journal of
Investigative Dermatology 125, 93–97; doi:10.1111/j.0022-202X.2005.23733.x, entitled, "Human Papillomavirus-DNA Loads
in Actinic Keratoses Exceed those in Non-Melanoma
Skin Cancers", actinic keratosis may contain a significant amount of infectious human papillomavirus.
Verbatim: "HPV presents in significantly higher viral loads in actinic keratosis, which are
the precursor lesions of squamous cell carcinoma, than in SCC.
Viral loads of 1 HPV-DNA copy per less than 50 cells were measured in 40% of AK.
The higher viral loads in AK are likely to reflect enhanced HPV-DNA replication.
This may be because of intense keratinocyte proliferation and differentiation in AK favoring
amplification of commensalic HPV.
Active HPV replication and presumably enhanced gene expression may in turn stimulate keratinocyte
proliferation and contribute to carcinogenesis in these early stages of NMSC development.
HPV-E6 proteins were recently shown to inhibit UV-induced apoptosis by abrogation of Bak
in response to UV damage and to bind a protein required for repair of single strand DNA breaks.
Thereby, accumulation of UV-induced mutations and oncogenic transformation might be facilitated
in cases of active HPV infection."
Treatment
5-fluorouracil appears to be the most effective treatment.
Various other treatments may also be used including:
Ingenol mebutate gel for treatment of the trunk and extremities or the face and scalp,
respectively.
Duration of therapy is 2 days for the 0.05% gel and 3 days for the 0.015% gel
Diclofenac sodium gel, a nonsteroidal anti-inflammatory drug, Recommended duration of therapy is 60
to 90 days Cryosurgery, e.g. with liquid nitrogen, by
"freezing off" the actinic keratosis Photodynamic therapy: this new therapy involves
injecting a chemical into the bloodstream, which makes the lesions more sensitive to
any form of light.
Laser, notably CO 2 and Er:YAG lasers, a laser resurfacing technique
is often used with diffuse actinic keratosis Electrocautery: burning off actinic keratosis
with electricity Imiquimod, an immune enhancing agent for topical
treatment Different forms of surgery
Regular follow-up after the treatment is advised.
The regular checks are to make sure no new lesions have developed and that old ones haven't
become thicker.
Prognosis The risk of an actinic keratosis turning into
squamous cell carcinoma is between 0% and 0.5% per year.
The latter risk is in those who have previously had skin cancer.
They go away in 15-60% of cases over a year.
In cases that resolve, they come back in 15-50% of people.
Epidemiology Actinic keratosis is very common, affecting
half of the global population.
It is seen more often in fair-skinned individuals, and prevalence may vary with geographical
location and age.
People who take immunosuppressive drugs, such as organ transplant patients, are 250 times
more likely to develop actinic keratoses that may lead to skin cancer.
Research A number of medications are being studied
including: afamelanotide, gefitinib, and cetuximab among others.
References
External links Actinic Keratosis
American Academy of Dermatology Actinic Keratosis photo library at Dermnet