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Dermatoscopic skin structures
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dermatoscopic skin structures

Dermatoscopy is a non-invasive technique producing high quality pictures of structures below the skin surface and invisible to the eye. Such structures are called dermatoscopic structures and have been found very useful in the analysis of melanocytic pigmented lesions.

Continuing development of the technique has enabled clinicians to view more regions of the skin sub structures in better detail. This helps in getting more accurate diagnosis of skin diseases and designing better treatments.

Dermatoscopic Structures

In the study of dermatoscopic skin structures, it is necessary to be familiar with some technical terms that describe these structures. Some of the major structures are listed below.

  • Pigment network is a regular honeycomb structure made of brown and black lines set on a diffused lighter background.
  • Branched streaks are broadened, branched lines resulting from a broken pigment network.
  • Dots and globules are sharply circumscribed, oval or round structures of different sizes of brown, black or gray colors. Dots are defined as less than 0.1mm in diameter.
  • Streaks are light brown to black linear structures distributed regularly or irregularly within or at the edge of a lesion. Some authors call them radial streaming when they are radially directed at the lesion edge and pseudopods when they are fingerlike projections at the edge of the lesion.
  • Structureless areas are areas without any dermatoscopic structures. They are called blotches when they are hyperpigmented in brown, black or gray colors. When the pigmentation is reduced they are called hypopigmented areas.
  • Milia-like cysts are white or yellow round areas.
  • Comedo-like openings are round, oval or irregularly shaped crater-like structures of brown-yellow or brown-black colors.
  • Arborizing vessels are tree-like branching vessels.
  • Maple leaf-like areas are maple shaped brown to blue-gray pigmented areas normally at the periphery.

Analysis of Pigmented Lesions

The dermatoscopic structures are used to analyse pigmented lesions. It is a two-step process.

First step: To differentiate melanocytic from nonmelanocytic pigmented lesions.
In a melanocytic lesion there must be a pigment network, aggregated globules, branched streaks and homogenous blue pigmentation. In the absence of these features, other features present in non-melanocytic lesions like milia-like cysts, comedo-like openings, arborizing vessels, maple leaf-like areas or globules should be looked for.

Second step: To differentiate benign from malignant melanocytic lesions
Once melanocytic lesions are identified, one of several methods is used to differentiate benign lesions from the malignant ones. All use different algorithms.

Pattern analysis: This is the most difficult and diagnostically the most accurate method. It needs a detailed qualitative multiple dermoscopic evaluation. The disadvantage here is that its accuracy depends greatly on the expertise of the dermatologist. Several studies have shown that the accuracy of this method is lower in less trained dermatologists.

ABCD rule: This is a simpler method which uses four criteria. A stands for symmetry, B for border, C for color and D for differential structure. Based on various parameters and formulas scores are assigned to these criteria and added to get the total. If the total is less than 4.75 the lesion is probably benign and if it exceeds 5.45 it is likely to be malignant. Pigmented lesions with a score between these two figures should be suspected for melanoma.

The usefulness of this method was proved in a study on 194 pigmented skin lesions. The results showed 92% sensitivity and 91% specificity.

Seven features for melanoma is an algorithm based on seven dermoscopic criteria that predicted melanoma. These are regression-erythema, radial streaming, irregularly distributed pseudopods, lack of homogeneity, irregular pigment network and sharp margin at the edge. Scores are allotted to these features and added up. A total score of 2 or more is considered malignant and less than 2 is taken as benign.

Seven point checklist: It is a simplified pattern analysis suitable for non-experts. The method uses a seven-point checklist based on features usually seen in malignant melanoma. The seven-point checklist is divided into major and minor criteria. The major criteria get a score of 2 and the minor ones get a sore of 1 and the total obtained. Melanoma is diagnosed if the total is equal to or more than 3.

Conclusions

There was doubt, until recently, among dermatologists about the usefulness of dermatoscopy. Evidence, now available, proves that dermatoscopy in the hands of expert dematologists, is superior to the naked eye in detecting melanoma. But doubts persist about its place in the wider world of dermatology. In the future, it is hoped, emerging advanced techniques will be better able to diagnose malignant melanoma.

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