ABCD rule
The ABCD rule is the first dermoscopy algorithm created to help differentiate benign from malignant melanocytic lesions. This algorithm, described by Stolz, is based on multivariate analysis of four criteria (asymmetry, border, colors and different structures) with a score system. The total dermoscopy score (TDS) is calculated using a linear equation, with this TDS, a grading of lesions is possible with respect to the probability that the lesions under investigation are malignant. It is a reliable method that improves the diagnostic performance of nonexperts evaluating pigmented skin lesions [1] [2] [3] [4].
Asymmetry
The lesions should be bisected in perpendicular axes. The distribution of colors and structures and the contour of the lesions are evaluated on either side of each axis. If asymmetry is absent with respect to both axes within the lesion, then the asymmetry score is 0. If there is asymmetry in only one axis then the asymmetry score is 1. If there is asymmetry in both axes, then the asymmetry score is 2. The asymmetry score (0-2) is multiplied with 1.3 in order to calculate the A contribution to the TDS.
Border
The evaluation of the border score is related to the presence of a sharp, abrupt ending of pigment pattern at the periphery of the lesion or a gradual, indistinct cutoff. For the purpose of analysis, the lesions are divided into eight segments. When the entire border (i.e., in all eight segments) of the lesion shows an abrupt ending, the maximum border score of eight is given. Whereas if the border of the lesion in all eight quadrants has an indistinct cutoff then the minimum score of 0 is given. Minimum is 0 maximum is 8 and the factor 0,1 in order to obtain the total TDS.
Color
The following six colors are considered important. The presence of each color counts a 1 point and the factor is 0.5
- white
- red
- light brown
- dark brown
- blue-gray
- black
Brown, black, blue-gray colors correspond with melanin distribution, white color corresponds with regression and red color reflects the degree of inflammation or neovascularization. The color white is considered to be present only if the area in question is lighter (whiter) in color than the adjacent color of normal skin. The values for the color score range from 1 to 6.
Dermoscopic structures
For evaluation of dermoscopic (also known as differential) structures, five main features are considered. For the presence of each structure a value of 1 is attributed. The multiplication factor is 0,5
- Structureless areas
- Pigment network
- Branched streaks (atypical network)
- Dots
- Globules
In general, melanomas display more dermoscopic structures as compared with nevi. Ninety percent of melanocytic nevi reveal three or fewer structural components. In contrast, 73% of melanomas reveal four or more structural components.
Calculation of the total dermoscopy score (TDS)
The individual scores of each component of the ABCD rule of dermoscopy is multiplied by the coefficients 1.3, 0.1, 0.5, and 0.5, respectively, obtaining a TDS. The threshold for benign lesions is: < 4.75, the TDS range for suspected lesions is: 4.76- 5.45 and the threshold for malignant lesions is: > 5.45.
Exceptions
There can be exceptions to the ABCD rule of dermoscopy. False-positive TDS can be seen in: melanocytic nevi with a lentiginous component, nevi with globules, nevi with a papillomatous component, Spitz/Reed nevus, congenital melanocytic nevus, nevus spilus, agminated nevus, recurrent melanocytic nevus and ink spot lentigo. Lesions of special sites such as face, palms, soles, and mucosa, have location-specific criteria for malignancy and they cannot reliably be analyzed using the ABCD rule. Not all melanomas will be correctly recognized with the ABCD rule of dermoscopy. Sometimes, the distinction can be extremely difficult, in particular for amelanotic melanomas, deep nodular melanomas, metastatic malignant melanomas, early melanomas. In these cases, it is important to search for other subtle structural components/clues such as regression structures, milky-red areas, and atypical vascular pattern.
- ↑ Argenziano et al.: Dermoscopy of pigmented skin lesions: results of a consensus meeting via the Internet. J. Am. Acad. Dermatol. 2003;48:679-93. PMID: 12734496. DOI.
- ↑ Argenziano 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. PMID: 9875194.
- ↑ Ahnlide et al.: Validity of ABCD Rule of Dermoscopy in Clinical Practice. Acta Derm Venereol 2016;96:367-72. PMID: 26351008. DOI.
- ↑ Stolz et al.: Principles of dermatoscopy of pigmented skin lesions. Semin Cutan Med Surg 2003;22:9-20. PMID: 12773010. DOI.
