Diagnosing Pigmented Skin Lesions
Talking with many consultant dermatologists and GPs reveals that one of the main problems of diagnosing and monitoring pigmented lesions is the issue of subjectivity. When two people look at the same, non-uniform object, the chances are that they will not describe its color and shape in exactly the same way. When two digital photographs of the same subject are taken, without complicated equipment and procedures there will be subtle differences in lighting, angle and distance to the object, all things that can make the two pictures appear non-identical. Whether based on the expertise of the dermatologist, built up over years of specialization, or the ‘gut reaction’ of a GP seeing something new, it is extremely difficult to bring uniformity to diagnosis and treatment monitoring where the skin is concerned.
Up until now, getting simply a more detailed look at the surface of the skin has been the aim of skin imaging techniques. However, better magnification does not automatically lead to better classification when it is still only the eye that decides, based on color and shape alone. Health practitioners who examine or treat the skin need an objective, rigorous and repeatable way of characterizing and diagnosing lesions that can be reproduced and matched or compared in other clinical settings. Such a method needs to generate images, but these images must be backed up with spectroscopic data. It is the spectroscopic data, rather than the images, that actually determine the parameters for diagnosis.
Better diagnosis can mean more timely and appropriate treatment, and reduce the number of false positives. In the US numbers there are around 2.5 million ‘excess’ excisions annually. Given these figures, it is not hard to imagine the impact that more accurate diagnosis could have on patient throughput and waiting lists. Better diagnosis can prevent disfigurement where cancer is not confirmed and, in the case of malignant melanoma, save lives.
Many doctors are now looking beyond traditional methods and seeking modern ways to aid their diagnosis and increase consultation efficiency, and many of them are using an advanced, clinically proven, non-invasive skin imaging technique called SIAscopy, Spectrophotometric
SIAscopy allows you to examine the skin to a depth of 2mm, and shows concentrations of hemoglobin, pigment and collagen. It is proving to be not only a valuable aid to diagnosis, but also a reliable method for obtaining objective data for baseline purposes or for referral.
Acne, eczema, psoriasis, warts and skin tumors are amongst the commonest of all human disorders. Thus it is hardly surprising that ‘skin diseases account for about 15 per cent of a general practitioner’s workload’ (Marks 2003). The skin is the body’s largest organ and highly complex in structure and function. Skin disorders can be general or localized in particular areas of the body. They are frequently instantly visible and can have devastating physical, emotional and psychological effects so fast and accurate diagnosis can be key to patient wellbeing and a successful treatment outcome.
A large number of skin conditions present as pigmented skin lesions, discolorations of areas of skin due to an underlying physiological problem. Pigmented skin lesions can be confined to the stratum corneum, or penetrate deeper into the epidermis and dermis, and may also expand upwards from the skin’s surface. They range from the benign to the life-threatening, and from those that are merely a nuisance to those that are completely debilitating.
The skin condition that requires the most urgent diagnosis and treatment is skin cancer. There are 32 types of skin tumor, from the benign, such as squamous cell papillomas and haemangioma, to the malignant, such as basal cell carcinoma and Kaposi’s sarcoma. The most dangerous form of skin cancer is malignant melanoma, which spreads either horizontally (superficial spreading malignant melanoma, SSMM) or vertically downwards (nodular malignant melanoma, NMM), the latter being the more immediately life-threatening. Malignant melanoma has a very high five-year survival rate if treated early, and prognosis is closely correlated with the depth to which the malignant melanoma has penetrated into the dermis.
The color of the skin is mostly due to the concentrations of pigment and hemoglobin, and it is changes in these constituents that lead to the appearance of pigmented skin lesions. Pigment is synthesized by melanocytes and darker areas of skin indicate higher pigment production (rather than greater numbers of melanocytes). Coloration due to hemoglobin relates not only to concentration but also to degree of oxygenation.
Aspects of skin lesions that aid in diagnosis include not only color (shade and tone), but also shape, how well-defined the edges of the lesion are, and size. Given the vast array of different types of skin lesions, it is not surprising that it can sometimes be difficult to distinguish between them. For instance, while some skin tumors have distinctive characteristics that make them more straightforward to diagnose, in many cases alternative conditions have to be ruled out. Seborrhoeic ketoses, for example, although easy to recognize, may be confused with ‘a pigmented cellular nevus, a pigmented basal cell carcinoma and, most importantly, with a malignant melanoma’ (Hunter et al, 2002).
Dermatologists address this difficulty in part through their extensive experience. They build up a mental database that enables them to arrive at their diagnosis by a process of comparison and elimination against similar conditions that they have diagnosed in the past. Scoring systems have been developed based on visible characteristics to aid the diagnostic process, but many of these have a large margin of error and this leads to significant numbers of false positive results.
Confirmation of this visual method of diagnosis can only be provided by microscopic analysis, which means removing some of the skin for
Biopsy is particularly common in cases of suspected malignant melanoma, due to the recognized risks of leaving a potential malignancy untreated. Excision includes a margin of skin surrounding the suspected melanoma, typically at least 2cm of skin around a melanoma of 1cm diameter
The expression, ‘if in doubt, cut it out’, is a familiar one, and typically one would expect the patient to prefer this option for certainty of a cure. However, melanoma is linked to exposure to the sun; therefore it is not surprising that the face, hands and feet are the most likely sites for melanomas.
Large excisions may disfigure the patient, and accuracy in diagnosis can go a long way towards preventing unnecessary scarring and disfigurement. Given that the ratio of biopsies performed to malignant melanomas confirmed can be as high as 100:1, more accurate diagnosis can also have a considerable impact on the efficient use of a clinician’s time and resources skin lesions, giving the practitioner a better view of color distribution, shape and the margins of the lesion.
Dermatoscopy is a specialized form of illuminated magnification, using a fluid (mineral oil, alcohol or water) to eliminate surface reflection from the skin and magnifying the lesion by a factor of 10. This method requires formal training, but the trained practitioner is then better able to assess visually pigmented structures in the epidermis and superficial dermis. Dermatoscopy is combined with digital photography to give the practitioner a record of each lesion at each visit. Automated scoring systems, such as ABCDE, compare dermatoscopic images against a large database for best fit.
The newest aid in the diagnosis of pigmented skin lesions is SIAscopy, or Spectrophotometric Intracutaneous Analysis, which provides spectroscopic data about a skin lesion without the need for laboratory analysis and so takes the subjectivity out of clinical examination. SIAscopy is unique in that it allows the practitioner to view beneath the surface of the skin. It uses white light and sophisticated software to provide independent views of pigment, dermal pigment, hemoglobin and collagen in the stratum corneum, epidermis and dermis to a depth of 2mm. The images (SIAscans) can be viewed separately or overlaid, to demonstrate how the features relate to one another, and help to make any necessary excision more precise by showing the exact size of a lesion. SIAscopy is a completely safe, non-invasive and painless technique, which makes it ideal for analyzing and monitoring many skin conditions, including skin cancers, psoriasis, acne, eczema, skin de-pigmentation, skin aging and scars.
The technique is available in two methods, contact and non-contact SIAscopy. How SIAscopy works is described in more detail below.
How SIAscopy works
SIAscopy measures the amount of hemoglobin, pigment, collagen in the stratum corneum, epidermis and dermis to a depth of 2mm, and identifies whether pigment is present in the epidermis or the dermis.
The information is presented to the practitioner as SIAscans, which show how these components vary over the skin. SIAscopy makes use of the way light interacts with skin – the way it scatters or bounces and the amount absorbed by cells and other structures – and how this varies for different wavelengths or colors of light. Due to the multi-layered structure of the skin, and because the most prominent chromophores have slowly varying spectral properties, it is possible to generate models which can predict the method of light transport within skin. This allows us to analyze the skin using broadband spectrophotometric techniques.
By sending light into the skin and measuring how it emerges back out, SIAscopy is able to determine the nature and position of many of the different cells and structures within the skin. Different primary wavelengths of light are shone into the skin in turn. An imaging chip records the light remitted from the skin at each pixel, giving an image representing the amount of light leaving the skin for each of the four wavelengths used. Cross polarizer are used to remove any scattering from the surface of the skin.
In order to generate the model, simulations are run for hundreds of thousands of different combinations of hemoglobin, pigment, collagen and dermal pigment. The result of each simulation represents how the camera would respond if it was to image the corresponding combination of skin chromophores. This information is stored, and then interrogated during each scan in order to generate SIAscans. Each SIAscan is a bitmap representing the concentration of each chromophore on every pixel. Each scan is made up of more than 1.5 million measurements.
The FDA approved SIMSYS-MoleMate Skin Imaging System, a non-invasive skin cancer screening procedure, is a significant advance in the early detection of potentially life threatening moles and lesions.
Physicians have found the SIMSYS-MoleMate Siascope hand-held device easy to learn and use, and that it rapidly provides accurate images of the pigment, blood, and collagen below the mole or lesion.
Now, for the first time, physicians can more accurately evaluate suspicious moles and lesions in a non-invasive, pain-free way. Experts also believe it may reduce the need for time consuming and expensive biopsies.