Polarised or Non-Polarised?

Before answering this question, a look at how the dermatoscope works is helpful.  The dermatoscope allows us to see the colours and microstructures of epidermis, dermo-epidermal junction and the papillary dermis, which are not visible to the naked eye.  It does this in one of 2 ways.

Non-polarised light source.  By using a fluid between a glass plate and the skin, reflection of light from the surface of the skin is eliminated, allowing visualisation of deeper structures.  The first generation of dermatoscopes used this method and much of the early research was done in Europe using this method.

Polarised light source and a polarising filter at 90 degrees (cross polarisation).  Reflected light from the surface is blocked, and light reflected from deeper structures is clearly seen.  More recent research, especially that from Australia, used this method, discovering new structures which can only be seen using cross-polarisation.

Which is better?

There is no simple answer; both have their advantages and disadvantages.

The main drawback of non-polarised dermoscopy is that it requires contact with the skin and the use of a fluid.  With polarised dermoscopy, both are optional, but for photography, contact eliminates camera-shake, and fluid may improve image quality.  There are some important features which are better visualised with non-polarised, and others seen better with polarised dermoscopy.  Some structures can only be seen with one type.  In addition, vessels can be squashed using contact dermoscopy.

Why not have the best of both worlds?

In conclusion, if you are serious about dermoscopy, use a hybrid model.  These are dermatoscopes which have both non-polarised and polarised light settings, and the ability to toggle between them.

References

Pan Y. Polarized and nonpolarized dermoscopy: the explanation for the observed differences. Arch Dermatol. 2008 Jun;144(6):828-9.

Marghoob A, Cowell L, Observation of chrysalis structures with polarized dermoscopy.  Arch Dermatol. 2009 May;145(5):618.

Haspeslagh M. Rosettes and other white shiny structures in polarized dermoscopy: histological correlate and optical explanation. J Eur Acad Dermatol Venereol. 2016 Feb;30(2):311-3.

Click here for further information on DermLite dermatoscopes.

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The Medical Journal of Australia – published 9 May 2022

Professor David Whiteman and Professor Anne Cust

MELANOMA is a common cancer in Australia. Each year in this country, more than 16 000 people are diagnosed with invasive melanoma, and almost twice that number are diagnosed with in situ disease. Unfortunately, around 1300 Australians will die from melanoma this year. But while Australia and New Zealand hold the unenviable position of having the world’s highest incidence rates of melanoma, a recent publication, of which we were co-authors, highlights the fact that melanoma is becoming increasingly common in other parts of the world.

Arnold and colleagues analysed cancer registration data from across the world to provide a snapshot of the global burden of melanoma. We estimated around 325 000 new cases of melanoma worldwide in 2020, and around 57 000 deaths from melanoma. Further, we measured recent trends in melanoma incidence and deaths in each country, broken down by age group and sex, and then assuming that current underlying trends will continue into the future, we projected likely patterns of incidence and mortality out to 2040. Under those assumptions, we estimated that the global melanoma burden will grow to 510 000 new cases per year and 96 000 deaths per year by 2040. To read more click here

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A Brief History of Dermoscopy.

The first handheld dermatoscopes became available in the late 1980s and over the ensuing 2 decades both the instruments themselves and the science underpinning their use were refined, initially for pigmented lesions and later for non-pigmented lesions.  Training courses, both face-to-face and virtual, were developed so that dermatoscope users could understand and interpret the colours and structures they were seeing.  Today, there is overwhelming evidence that dermoscopy significantly improves the accuracy of diagnosis of skin lesions.

What is Dermoscopy?

A non-invasive method to view and evaluate in vivo the colours and microstructures of epidermis, dermo-epidermal junction and the papillary dermis, which are not visible to the naked eye.  The dermatoscope eliminates surface reflection making the stratum corneum transparent and allowing examination of the epidermis and superficial dermis.  Most dermatoscopes provide x10 magnification.

Why Has the Dermatoscope Become Essential?

Australasia has the highest incidence of skin cancer in the world. The sheer volume of disease means that the diagnosis and management of most skin cancer is carried out in primary care with only the more difficult, sinister or advanced tumours being referred into secondary care.  A high level of diagnostic accuracy amongst GPs is essential in order to avoid missing melanomas and at the same time to reduce unnecessary excisions of benign lesions.  A recently published document, Quality Statements to Guide Melanoma Diagnosis and Treatment in New Zealand, includes the following.

All primary health care professionals involved in early detection of melanoma should be trained in the use of the dermatoscope and regularly undertake refresher training.

In primary health care practices, [patients should have] access to at least one designated primary health care professional trained in the dermatoscopic diagnosis and management of melanoma.

Training.

Medical students all receive training in the use of the scopes mentioned at the start of this article.  Some universities now include some dermatoscopy training their curricula, but for those who trained in the previous millennium, there was none.  In the same way that dermatopathologists require training to be able to accurately diagnose what they see under the microscope, so do dermatoscopists.  However, there is good evidence that, for the novice, a few hours training and the use of an algorithm significantly improves diagnostic accuracy.

“Can you please have a look at this spot on my skin?”

As a GP, how many times have you been asked this at the end of a consultation?  If you have a dermatoscope on your desk and have undertaken the training, you can examine the lesion and quite rapidly assign it to 1 of 4 categories.

1. A confident, specific, benign diagnosis.
2. Clearly malignant and requires excision.
3. Suspicious and requires either excision or biopsy.
4. Don’t know.

With increasing expertise, the number of lesions in category 4 will reduce and those in category 1 will increase.  At the same time, the patient, whose trust in you has just been enhanced, can be encouraged to attend for a full skin check.  Experienced dermoscopists have much greater confidence in making benign diagnoses, reducing the frequency of, “If in doubt, cut it out”.

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