Dermoscopy of seborrhoeic keratosis

Created 2008.

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 – there are two types:
  • Tiny white starry
  • Larger yellowish cloudy
• 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.

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

Starry and cloudy milia-like cysts

Irritated lesion

Hairpin blood vessels

Exophytic papillary structures

Identification of seborrhoeic keratoses by Chaos and Clues method

Seborrhoeic keratoses demonstrate "chaos" by modified pattern analysis, ie, they often have asymmetry of colour and structure on dermatoscopy — like pigmented skin cancers. Clinical clues to seborrhoeic keratoses are:

• Multiple grouped similar lesions
• Stuck-on lesion
• Waxy or scaly surface

Dermatoscopic clues to seborrhoeic keratoses by modified pattern analysis are:

• Multiple orange clods
• Multiple white clods
• Thick curved lines
• Sharply demarcated border over total periphery

If features are equivocal, excise the lesion. Partial biopsy may be acceptable if low-risk lesions, providing full excision is arranged should the atypical lesion prove to be melanocytic.

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)