Non-invasive examination by dermoscopy

Dermoscopy is a non-invasive diagnostic technique for visualising the surface and subsurface of skin lesions. The average magnification is 10x, which allows the user to see morphological structures that are normally invisible to the naked eye.

This leads to improved diagnosis and differentiation between malignant and non-malignant lesions. Dermoscopy allows in vivo examination, which can be repeated at follow-ups. This can reduce the number of benign lesions excised owing to diagnostic uncertainty.

Instruments range from a basic ophthalmoscope to advanced videodermatoscopes. Probably the most common is the handheld dermoscope. Low cost, portable and easy to use, this provides fixed 10x magnification and fixed dermal and subdermal illumination via halogen bulb or LEDs.

Basic dermoscopes can be non-contact, such as the Dermlite , or an oil immersion type, such as the DermoGenius 2. The Dermlite is held like a magnifying glass, above the lesions, and moved in and out to focus. DermoGenius 2 uses a small amount of immersion oil placed over the lens, which then makes contact with the skin at a fixed distance, with no need for focusing.

If you wish to record images, one option is a Dermatophot, a special lens that can be mounted on a digital camera, allowing macrophotographs to be taken and stored. Again, these have
10x magnification and a light source, but also allow images of non-excised lesions to be compared with follow-up images.

For the more ambitious, there is the stereomicroscope, giving a binocular three-dimensional image with magnification from 6x to 40x and three light intensities.¹ A digital or video camera can be connected to it. Photographic and video dermoscopy can be particularly useful in allowing clinicians based elsewhere to observe lesions in great detail.^2,3

Dermoscopic differentiation
Pattern analysis is the classic approach for dermoscopy, in which global patterns and local features are examined. Patterns include reticular (a pigmented grid of thin brown lines over a light brown background network on most of the lesion, typically seen in melanocytic lesions) and multicomponent (three or more distinctive dermoscopic structures in a lesion, such as zones of pigment network, clusters of dots or globules and areas of diffuse hyper- or hypopigmentation, suggestive of a malignant melanoma). Other types include starburst, globular, parallel and homogenous patterns.

The next step is to look at local features, such as pigmentation, dots and globules, streaks, blue-whitish veils and regression structures. All of these have diagnostic significance.

As one example of a lesion and its dermoscopic features, consider the basic blue naevus. Blue naevi commonly reveal distinct features that allow diagnosis with a high degree of certainty. Clinically, they appear as regular, well-circumscribed macules, papules, plaques, or nodules, with uniform blue pigment, and are generally easy to diagnose. Their dark appearance will often raise concern that they are melanomas.

This is where dermoscopy can be helpful. Closer inspection reveals that they exhibit a homogenous pattern, with complete absence of local features, such as pigment networks, globules, or black dots surrounded by a well-defined border – not the features of a malignant melanoma.

Diagnostic algorithms
Problems inherent in pattern analysis led to the development of two other methods – the ABCD rule of dermoscopy and the seven-point checklist. In both, initial differentiation between non-melanocytic and melanocytic lesion is essential. The ABCD rule looks at Asymmetry, Border, Colour and Differential dermoscopic structures of a given melanocytic lesion.⁴

The seven-point checklist is specifically for dermoscopic diagnosis of malignant melanomas. Major criteria (atypical pigment network, blue-whitish veil, atypical vascular pattern) score two points; minor (irregular streaks/pigmentation, irregular dots/globules, regression structures) score one point. At least three points are required for diagnosis of a melanoma.⁵

Conclusion
The significance of a missed melanoma makes urgent referral of suspicious lesions of paramount importance. Yet benign-looking lesions are still regularly referred under the two-week rule, which blocks appointments and causes unwarranted anxiety.

Dermoscopy might not reduce this, but it remains a low cost, easy alternative to the naked eye, for anybody who wishes to improve their dermatological diagnostic skills.

- Dr Nigel Stollery is a GP in Kibworth, Leicestershire, and clinical assistant in dermatology at Leicester Royal Infirmary

References
1 Soyer HP, Smolle J, Hödl S et al. Surface microscopy: A new approach to the diagnosis of cutaneous pigmented tumors. Am J Dermatopathol 1989; 11:1-10.
2 Lesher JL, Davis L, Gourdin FW et al. Telemedicine evaluation of cutaneous diseases: a blinded comparative study. J Am Acad Dermatol 1998; 38:27-31.
3 Loane MA, Korbett R, Bloomer SE et al. Diagnostic accuracy and clinical management by real time teledermatology. Results from the Northern Ireland Arms of the UK Multicentre Teledermatology Trial. J Telemed Telecare 1998; 4:95-100.
4 Nachbar F, Stolz W, Merkle T et al. The ABCD rule of dermatoscopy. J Am Acad Dermatol 1994; 30:551-59.
5 Argenziano G, Fabbrocini G, Carli P et al. Epiluminescence microscopy for the diagnosis of doubtful melanocytic skin lesions. Comparison of the ABCD rule of dermatoscopy and a new 7-point checklist based on pattern analysis. Arch Dermatol 1998; 134:1563-70.