Dermoscopy

Introduction

Dermoscopy is a non-invasive diagnostic technique that enables recognition of morphologic structures not visible to the naked eye

This article provides an introduction to dermoscopy and will act as an aid when viewing the image atlas. In order to learn more we recommend the following resources:

• A superb online tutorial developed by the International Dermoscopy Society
• A dermoscopy tutorial available as an app on itunes
• The Interntaional Dermoscopy Society also offers free membership that enables users to email difficult cases for discussion with leading experts in the field
• Dermoscopy UK has a website developed by Dr Jonathan Bowling
• Dr Eric Ehrsam's dermoscopy website
• The PCDS frequently runs dermoscopy sessions – see events
• For additional images please refer to the dermoscopic section of the image atlas

Purpose of dermoscopy in primary care

• The main purpose is to aid in the diagnosis of skin lesions
• It must not be used in isolation but instead combined with history, naked eye examination and in appropriate cases histology
• Derrmoscopy should be performed by GPs (and specialists) who have undertaken training in the technique
• The ultimate aim is to help identify all lesions that MAY be melanoma and refer them to secondary care, while leaving behind those that are benign. Their is however a learning curve:
  • the majority of seborrhoeic keratoses, angioma, dermatofibroma, blue naevi and basal cell carcinoma can be readily identified using a dermatoscope, however
  • considerable experience is sometimes needed to differentiate between benign melanocytic naevi and melanoma, and some cases of melanoma have very subtle dermoscopic features
  • along the learning curve the fall back position should always be that if a diagnosis of melanoma cannot be excluded then the lesion should excised with a 2 mm margin or if suspicious of melanoma the patient should be referred to secondary care under the two-week rule

Equipment

Which dermatoscope?

Heine Delta 20 ®

• A contact dermatoscope
• Allows excellent image quality and provides a very stable attachment for a camera
• Drawbacks - need an interface medium so risk of cross infection. Also pressing the dermatoscope down too hard on lesions can blanch important vascular features
• In order to reduce the risk of cross infection and to provide the necessary interface medium it is advisable to use Purell ® hand gel , which is placed on the surface of the skin lesion. On nail lesions ultrasound gel sits better and may be preferable. The surface of the dermatoscope should be cleaned with an alcohol swab in between patients

The other contact surface dermatoscope is the DermLite II Fluid ®, which has a bigger surface aperture and so can be good for large lesions. However it does produce optical distortion at the edges and has no scale for measuring lesion size

DermLite II Pro HR ®

• The first cross-polarised dermatoscope with a bright image
• Advantages – as the  lens does not contact the skin there is less chance of cross infection. For multiple lesions it takes a shorter time to examine patients as their is no need to apply gel on to the skin
• Disadvantage – the appearance of the lesions are not quite as good as with the Heine Delta 20

The DermLite II Hybrid ® works in both ways i.e. contact and cross-polarised, but purists feel the image is not as sharp as with the Heine Delta 20

g>Camera and Adaptor
In order to make sure that equipment fits together it is advisable to contact companies who specialise in such matters such as Brymill and Schuco. Brymill have an all in one package that consits of a Heine Delta 20 dermatoscope, contact plate with scale, Sony W270 Cyber-shot camera and a lens adaptor with step down rings. It is possible to use dermatoscopes with SLR cameras and adaptors but they are more expensive

Software
In order to follow up patients it is important to have mole mapping software that allows for accurate comparison of skin lesions. One of the most useful is PhotoMax 2.2 that can be purchased from Schuco

Interpretation of dermoscopic features

The dermoscopic appearance of skin varies depending on site. The notes in this section can be applied to any body site except:

• Face - for more information please refer to the article on melanoma / lentigo maligna
• Palms & soles - for more information please refer to the article on melanoma / lentigo maligna
• Mucosal surfaces - the relevance of dermoscopic features in these sites is still unclear

In order to formulate a diagnosis it is important to understand the relevance of the different dermoscopic features, which can be grouped as follows:

- Pattern analysis

- Lesion specific features

- Colour and symmetry

Pattern analysis  

Should be viewed in two ways – pattern recognition and pattern comparison:

i) Pattern recognition

Every skin lesion can be placed in to one of nine groups, which will either help confirm a diagnosis or point in the right direction:

• Reticular pattern - defined by a pigment network. Typical pigment networks are seen in acquired melanocytic naevi and some lentigo. A fine peripheral network is seen in dermatofibroma. An atypical pigment network has a high specificity for melanoma

• Globular pattern - the presence of numerous, variously sized, round to oval structures with various shades of brown and gray-black coloration. A globular pattern is indicative of junctional proliferation of melanocytes and is normally seen in acquired melanocytic naevi in young people

• Homogenous pattern - a diffuse area of colour in the absence of a pigment network or other distinctive local features. Such features may seen in melanocytic lesions or other lesions such as blue naevi and some seborrhoeic keratoses

• Multicomponent - while it is not unusual to find a combination of features such as globular reticular or reticular homogenous, the combination of three or more patterns within a lesion (multicomponent) can be suggestive of melanoma, especially with increasing degrees of asymmetry

• Cobblestone - closely aggregated, large somewhat angulated globules resembling a cobblestone. They result from large dermal nests of melanoctyes found in dermal naevi

• Parallel pattern - indicative of acral lesions. A parallel-like fingerprint pattern can be seen in solar lentigo

• Starburst pattern - pigmented streaks in a radial arrangement at the edge of pigmented skin lesion. Indicative of spitzoid lesions including the pigmented spindle cell naevus of Reed, and spitzoid melanoma

• Lacuna - several to numerous, smooth-bordered, round to oval, variously sized structures. The morphologic hallmark of these lacunae is their striking reddish, blue-purplish or black coloration. They are indicative of angioma

• Unspecific - relatively featureless lesions that cannot be categorised by any of the above. Beware as it could represent a subtle melanoma

Patients with multiple acquired melanocytic naevi will often have lesions showing a similar dermoscopic pattern – any lesion found to have a different dermoscopic pattern, especially if showing other dermoscopic abnormalities should be treated with suspicion

It is important to take into consideration the patients age as the dermoscopic morphology of acquired melanocytic naevi change as patients get older such that it is predominantly:

• Globular in teenage years
• Reticular in 30-40 year olds
• Homogenous in the over 50’s

A lesion showing globular activity in older patients should be regarded with suspicion as one would not normally expect melanocytic proliferation in such patients. These images 1 | 2 | 3 | 4 demonstrate a 40 year old male with multiple melanoytic naevi - the first three lesions show a multifocal reticular pattern that was normal for him, but the forth lesion was predominantly globular and so was excised. The lesion was found to be  dysplastic

It is also important to take into account the skin phototype:

• Skin type I – pattern more commonly a homogenous centre with a peripheral reticular pattern
• Skin type III - more commonly a uniform reticular pattern

Lesion specific features (also known as local features)

Every lesion may have additional morphological features:

Pigment network - a typical pigment network of acquired melanocytic naevi is characterised by a light to dark-brown pigmented, regularly meshed and narrowly spaced network distributed more or less regularly throughout the lesion and usually thinning out at the periphery. An atypical pigment network, a dermoscopic criterion with high specificity for the diagnosis of melanoma, is characterised by a black, brown, or grey, irregularly meshed network, distributed more or less irregularly throughout the lesion and usually ending abruptly at the periphery. The lines of an atypical pigment network are often thickened

Streaks - brownish-black linear structures of variable thickness, not clearly combined with pigment network lines, and are most obvious at the periphery. Some streaks have a rather bulbous end and are termed pseudopods

• Irregular streaks are very likley to represent melanoma, especially when the streaks are distributed unevenly
• A symmetric, radial arrangement over an entire lesion is most commonly found in a pigmented spindle cell naevus of Reed

Dots and globules - sharply circumscribed, usually round or oval, variously sized black, brown or grey structures. They represent aggregations of pigmented melanocytes, melanophages or even clumps of melanin

• Regular shape / even distribution – more likely to represent benign melanocytic naevi
• Irregular dots and globules, especially if occurring at the periphery are more likely to represent melanoma
• Blue-grey globules and ovoid structures are found in basal cell carcinoma

Pigment blotch - a brown-black circumscribed area that precludes recognition of subtler dermoscopic features such as a pigment network, globules or vascular structures. An enlarging blotch, especially if at the periphery may indicate melanoma

Blue-white veil - an irregular, confluent, grey-blue to white-blue diffuse pigmentation caused by an acanthotic epidermis with focal hypergranulosis above sheets of heavily pigmented melanocytes in the upper dermis. It has a high specificity for melanoma

Regression structures - these are white scar-like areas caused by fibrosis in the papillary dermis and blue areas (grey-blue areas, peppering, multiple blue-grey dots) that result from variable amounts of melanophages. They are usually found in cases of melanoma undergoing regression

Vascular structures - the following structures are often found in the associated lesions, such findings are NOT exclusive

• Comma vessels – mainly dermal naevi, rarely in melanoma
• Hairpin vessels – seborrhoeic keratoses, but also in other keratinising tumours such as SCC. Peripheral hairpin-like vessels can sometimes be found in superficial BCC
• Lacunes – angioma
• Glomerular vessels – Bowen’s disease (images 1 | 2 )
• Arborising vessels – BCC
• Dotted vessels – melanoma, but can be found in other lesions  
• Linear irregular vessels – melanoma

Melanoma may show dotted vessels, linear irregular vessels or a polymorphous pattern with a variety of vascular structures. A diffuse milky-red area can also be found in melanoma

It can sometimes be difficult to differentiate between linear irregular vessels and hairpin vessels, the latter tend to be surrounded by a milky halo. On occasions vascular structures may not be of help and as always it is important to look at the whole lesion when formulating a diagnosis. The vessels in this lesion (I,II) cannot be classified as predominately hairpin, but the rest of the dermoscopic features are consistent with a diagnosis of a seborrhoeic keratosis

Milia-like cysts - variously sized, white or white-yellowish, roundish structures. Predominantly found in seborrhoeic keratoses, but are sometimes present in dermal naevi and BCC. Very rarely seen in melanoma

Comedo-like openings - brown-yellowish or brown-black, roundish to oval or even irregularly shaped, sharply circumscribed structures. Mainly found in seborrhoeic keratoses, sometimes dermal naevi

Leaf-like areas and spoke wheel projections - leaf-like areas are brown, brownish-grey to grey-black patches revealing a leaf-like configuration. Spoke wheel areas are radial projections from a well-circumscribed dark central hub. Both are predominantly found in BCC - their presence can be very subjective

Colour and Symmetry

While considering the pattern and lesion specific features it is important to assess colour and degree of symmetry

i) Colour

Skin lesions have a variety of colours including brown, black, blue, grey, white, yellow and red. In general the greater the number of colours the more likely the lesion is to be malignant. This is not always the case though as some melanomas are relatively non-specific and can be amelanotic / hypomelanotic

Understanding colour is also important as it helps determine the level of melanin in the skin:

• Black – superficial epidermis
• Brown – epidermis
• Grey – papillary dermis
• Blue – reticular dermis

ii) Symmetry

The degree of symmetry should be assessed when observing pattern analysis, lesion specific features and colour:

• In general, lesions with greater degrees of symmetry are more likely to be benign, where as
• Greater degrees of asymmetry are more suggestive of malignancy

Examples of symmetry:

• A typical pigment network of an acquired melanocytic naevus is characterised by a light to dark-brown pigmented, regularly meshed and narrowly spaced network distributed more or less regularly throughout the lesion and usually thinning out at the periphery
• A symmetrical fine peripheral pigment network found in dermatofibroma
• Uniform blue-grey homogenous pattern of a blue naevus

Examples of asymmetry

• An atypical pigment has a high specificity for melanoma. It is characterised by a black, brown, or grey, irregularly meshed network, distributed more or less irregularly throughout the lesion and usually ending abruptly at the periphery. The lines of an atypical pigment network are often thickened
• Irregularly sized dots / globules, especially if situated near the periphery may also suggest melanoma  

The degree of symmetry/asymmetry is quite subjective, accordingly it must be considered in combination with all other dermoscopic and non-dermoscopic features to help formulate a diagnosis

Diagnostic algorithm for skin lesions

A number of scoring algorithms exist for skin lesions such as the 3-point and 7-point checklist. While they can be of help they do have flaws and we do not recommend that they be relied on for deciding whether or not any given lesion is benign or malignant

What is of great value though is the algorithm below. In essence one works through this is as follows:

I) Is the lesion melanocytic? If it is, is it likely to be benign or malignant? Criteria for melanocytic naevi are:

• Pigment network
• Pigment globules
• Cobblestone pattern
• Parallel pattern
• Starburst pattern

II) If it is not melanocytic are their diagnostic criteria for dermatofibroma, blue naevi, angioma, seborrhoeic keratoses or basal cell carcinoma?

III) If none of the above can be identified the lesion is likely to be melanocytic and could represent a subtle melanoma

Diagnostic Algorithm for Skin Lesions