There are specific and diagnostic features that enable confident diagnosis of pigmented and non-pigmented actinic keratosis and squamous cell carcinoma in situ. Invasive squamous cell carcinoma can be difficult to diagnose by dermoscopy alone.
Hand-held dermoscopy can be useful to distinguish squamous scaly, eroded flat or infiltrated and non-pigmented lesions from basal cell carcinoma. It can be more difficult for the teledermoscopist, who is unable to palpate the lesion.
Actinic (solar) keratoses may be pigmented or non-pigmented and the dermoscopic diagnosis is made when the strawberry pattern is present. This refers to a erythematous pseudonetwork on facial skin, in which there are prominent yellowish hair follicles surrounded by a white halo.They may also look like a target. Pigmentation may be due to grey or brown dots and globules, or to a broken-up pseudonetwork, resembling lentigo maligna. Short curved red blood vessels may be prominent. Rosettes, i.e. groups of 4 white shiny follicular perifollicular spots, are a feature of sun damaged skin on polarised dermoscopy.
On non-facial sites, actinic keratoses present with uniform pink or tan-coloured background and prominent keratin (white or yellow scale).
The main features of actinic keratosis are:
Dermoscopy can be helpful for diagnosing pigmented intraepidermal carcinoma (Bowen disease, squamous cell carcinoma in situ), which presents as an irregular skin-coloured, pink or brown scaly plaque. Irregular clusters of so-called ‘glomerular vessels’ (coiled vessels) and/or globular vessels (small red clods) are characteristic. They may be associated with a scaly surface, small brown globules, linear greyish dots and/or homogeneous pigmentation. Pigmented structures may be seen arranged in lines. White circles may be present, often in irregular clusters. There may be superficial erosion and crusting.
Non-pigmented intraepidermal carcinoma can be difficult to diagnose by dermoscopy. Compared with basal cell carcinoma, there is more scaling and the vascular pattern is glomerular/globular rather than arborising/branched. Background hue tends towards and orange shade of pink, whereas basal cell carcinoma tends to have more blue tone. Using polarisation, white shiny ‘crystalline’ structures are uncommon but may form rosettes on facial skin (keratin around follicles). Compared to psoriasis, the lesion is asymmetrical and the structure irregular.
Cutaneous invasive squamous cell carcinoma (SCC) is very variable in clinical appearance depending on the degree of differentiation and body site. It presents as a thickened plaque or nodule.
Look for white circles in actinic keratoses, squamous cell carcinoma in situ and invasive squamous cell carcinoma.
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Developed in collaboration with the University of Auckland Goodfellow Unit in 2007.
Author: Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, 2008.
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