Porokeratosis
Author: Dr Amy Prideaux
Chief Editor: Dr Daniel Keith
Macroscopic Appearance
A porokeratosis is a benign lesion which is often associated with a chronic history of UV exposure (although they can also be hereditary). The risk of malignant transformation is extremely low, however the larger the lesion, the more likely it is to become malignant. Patients should therefore be advised to avoid UV exposure to reduce the risk of transformation to SCC or BCC.
The key to identifying a porokeratosis is the raised pigmented or non pigmented train track margin that is often palpable and corresponds to the histological structure called "cornoid lamella".
Macroscopically, a porokeratosis is an annular (ring shaped), well demarcated lesion with a central crater which is often scaly.
The annular ring is a raised peripheral area of increased keratin deposition which is often palpable and can be non pigmented (as in this example), or pigmented (as in the example below).
Here is another macroscopic image of a porokeratosis on the dorsal aspect of the hand. The central crater as well as the raised border here is relatively hyper-pigmented compared to the above image which simply indicates another variant of the lesion.
Dermoscopic Appearance
*Hallmark feature*
Peripheral 'tram track' marking - this can sometimes resemble a train track with it's double margin and can be pigmented or non pigmented
Other features
-
Pale centre - this is homogenous and appears almost scar like
-
Red-brown dots and globules
Dermoscopic features:
-
The black arrows highlight the hallmark feature of porokeratosis - the peripheral 'tram track' which in this case is non pigmented. The train track (double margin) appearance can also be appreciated in some areas of this image.
-
The pale centre is clearly seen contained within the peripheral white border
-
Red-brown dots and globules depict blood vessels which are usually present within the pale centre. These can be seen more clearly towards the periphery of the pale centre.
Sometimes, depending on the subtype of porokeratosis, the peripheral tram track border can be hyperpigmented and the central crater can appear more brown in colour.
This is a normal variant and you can see both of these features in this example.
Another macroscopic example of a porokeratosis.
You can appreciate the annular shape with it's well defined, hyper-pigmented border.
This is the same porokeratosis under the dermatoscope.
Although not quite as clear as in the examples above, you can make out the hyperpigmented border which is the hallmark feature!