Dermoscopy of seborrhoeic keratosis

Learning objectives
Introduction
Dermoscopic features of seborrhoeic keratosis
Activity

Learning objectives

• Describe dermoscopic features of seborrhoeic keratosis

Introduction

Dermoscopy is useful to distinguish pigmented non-melanocytic lesions from benign and malignant melanocytic lesions. There are specific features that help to distinguish seborrhoeic keratosis from basal cell carcinoma and melanoma. However, the distinction is not always possible and it may be necessary to excise some clinically atypical but histologically benign lesions.

The ‘wobble sign’ may be useful to distinguish a papillomatous melanocytic naevus from a stable seborrhoeic keratosis.

Dermoscopic features of seborrhoeic keratosis

Seborrhoeic keratoses typically reveal dermoscopic features that are fairly specific for the diagnosis. However, on occasions, melanocytic lesions, especially dermal naevi, congenital naevi, Spitz naevi and nodular melanoma, may have similar features and can be just as difficult to distinguish from seborrhoeic keratoses by dermoscopy as clinically.

Seborrhoeic keratoses can have an irregular structure and multiple colours (skin coloured, pink, grey, yellow, tan, dark brown, black, bluish).

Typical dermoscopic features include:

• Milia-like cysts
• Irregular crypts
• Fissures/ridges
• Blue-grey globules
• Light brown fingerprint-like parallel structures
• ‘Fat fingers’ (the gyri of a cerebriform surface)

There may also be a faint network or pseudonetwork. Blood vessels can be prominent in some seborrhoeic keratoses, tending to arise as tiny hairpin shaped capillaries surrounded by a halo within a lobule.

Dermoscopy of seborrhoeic keratoses

White lesion	Pink lesion	Brown lesion	Black lesion
Skin-coloured lesion	Blue-grey globules	Multiple colours	Multiple colours
Milia-like cysts	Horny cysts	Irregular crypts	Fissures/ridges
Fingerprint-like structures	‘Fat fingers’	Cerebriform pattern	Indistinct structure
Globule-like structures	Tanning cream in crypts	Brown dots	Irregular structure

Activity

Evaluate 20 pigmented seborrhoeic keratoses by dermoscopy. What proportion contain each of the following features:

• Pigment network
• Milia-like cysts
• Irregular crypts
• Fissures
• Multiple colours (3 or more)

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