Actinic Keratosis
Author: Dr Amy Prideaux
Chief Editor: Dr Daniel Keith
Actinic Keratosis are also known as as solar keratosis or solar warts. They are benign partial thickness dysplasia of the epidermis caused by chronic sun exposure. They are considered pre-malignant, however the risk of transformation to squamous or basal cell carcinoma is low. It is important patients monitor these and protect themselves from the sun to reduce their overall risk going forward.
A macroscopic example. This patient was referred with a red lesion on the nose which was scaling and irritating over many years but not noticeably growing.
Introduction
Macroscopic Appearance
Actinic keratosis often appears on chronically sun exposed areas such as on the face, ears and scalp, although they can occur anywhere on the body. They can be single lesions but often there can be multiple present.
They are usually pink, red or skin coloured areas of thickened skin which can vary in size and shape. The surface is often slightly scaly, but can also be smooth/flat or even hyperkeratotic, where there is excessive keratin deposition present leading to a horn like appearance in some cases.
A macroscopic example on the right cheek of this patient showing a scaly, pink/red lesion.
Dermoscopic Appearance
The 'Strawberry Pattern'
Dermoscopically, actinic keratosis are said to have characteristic features of yellow or white dots, on a red background. This is also known as the strawberry pattern.
Ignore the purple markings here, that is felt tip pen used to mark an area
Dermoscopic example (unannotated)
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The strawberry pattern is clearly visible in the centre of this image
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Towards the right middle and lower area you can see the rosette pattern with the four white/yellow dots
Dermoscopic example (annotated)
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Central strawberry pattern (black circle)
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Rosette/4 dot clods (blue circles). See below for further information about this sign!
'Rosettes' or '4 dot clods'
These are another feature of actinic keratosis, but they can also be seen in squamous cell carcinomas (SCC). Therefore it is important to correlate clinically. For example if they are seen in the context of a rapidly enlarging lump your clinical suspicion of an SCC must be higher, however if the context is otherwise inkeeping with an actinic keratosis, this feature can help confirm the diagnosis.
Dermoscopically, they are a collection of four little white dots.
NB The rosette sign can only be seen with polarised light!
Unannotated dermoscopic example showing multiple white 4 dot clots/rossetes. The strawberry pattern as above can also be visualised here.
In this zoomed in annotated version of the same image, you can clearly see the 4 white dots or rosettes (black circles). There are many more in this example which have not been circled!