Differentiating between shades of dermoscopic blue colors increases diagnostic accuracy

Key Points

Modena, Italy - A blue color witnessed in dermoscopy has always been a clue for malignancy, and immediately becomes a cause for caution and even worry for the experienced dermatologist. However, a blue tint is also sometimes observed in benign lesions, and this may, at times, leave the dermatologist in a diagnostic limbo.

According to a recent study using confocal microscopy, blue hues can better be categorized according to their pathologic substrates into inflammatory or tumoral cells, helping to increase the accuracy of diagnosing malignant lesions.

"Not every blue color or hues of blue color have the same substrate in dermoscopy. Confocal microscopy - thanks to its possibility to, in vivo, visualize the skin at cellular level resolution - is able to distinguish between blue hues consisting only of inflammatory cells, and blue hues derived from dermal infiltration of tumoral cells, leading to very different diagnoses and having very different consequences in regards to treatment," says Giovanni Pellacani, M.D., department of dermatology, University of Modena and Reggio Emilia.

The goal of the study was to identify the cytologic and architectural correlates of the dermoscopic blue hue by means of in vivo reflectance-mode confocal microscopy (RCM) to improve diagnostic accuracy in melanocytic lesions presenting with dermoscopic features for malignancy.

When describing the shades of blue seen, "blue areas" and a "blue-whitish veil" were defined as small diffuse or speckled zones with a gray-blue or gray hue and an irregular, confluent, gray-blue to whitish-blue, structureless pigmentation with an overlying ''ground glass'' film, respectively, although this distinction is frequently observer-dependent.

Dr. Pellacani found that out of the 213 cases studied, 84 lesions (39.4 percent) were observed to have a blue hue and, subsequently, suspected of malignant melanoma and were excised. The blue hue was seen in 38 out of 57 malignant melanomas (66.7 percent), 15 out of 27 Spitz nevi (55.5 percent) and 31 out of 129 acquired nevi (24 percent).

"On the whole, in our selected study population, the identification of a blue hue was suggestive of malignant melanoma diagnosis, although present in 29.5 percent of benign lesions. In accordance with the dermoscopic distinction of the blue hue, blue areas and blue-whitish veil were concordantly reported in 48 and 20 cases, respectively, with 95 percent specificity for malignant melanoma diagnosis for the latter. A discordant description of the blue (''unclassified blue'') was given in 16 of 84 cases (19 percent) showing a blue coloration," Dr. Pellacani tells Dermatology Times.

Dr. Pellacani explained that when using RCM, "blue veil"- very specific but low sensitive for melanoma diagnosis - is characterized by the contemporary presence of epidermal and dermal features consistent with diagnosis of melanoma, such as a disarranged pattern, pagetoid cells, cytologic and architectural atypias, nonhomogeneous and cerebriform clusters and dermal nucleated cells.

"Blue areas," observable in both benign and malignant lesions, are characterized only by plump cells corresponding to melanophages and inflammatory infiltrate in nevi and plump cells along with large nucleated atypical cells corresponding to malignant melanocytes infiltrating the papillary dermis, in melanomas.

According to Dr. Pellacani, the presence of at least two RCM alterations - one from the epidermis (disarranged superficial layer pattern, presence of roundish pagetoid cells, nonedged papillae or cytologic atypia) and one from the dermis (nonhomogeneous nests, cerebriform nests, or isolated cells infiltrating dermal papilla) - was able to expose 35 of 38 malignant melanomas, showing a 92.1 percent sensitivity and a 68.9 percent specificity.

This corresponded to the misclassification of nine of 14 Spitz nevi (64.3 percent) and five of 31 acquired nevi (16.1 percent), highlighting the importance of the confocal microscopy method.

"RCM is a new in vivo technique, which permits the visualization of the skin at a limited depth but at a quasi-histologic resolution, and it proved to be invaluable in distinguishing benign from malignant lesions," Dr. Pellacini say.

"In our study, we demonstrated the possibility of not only visualizing in vivo the cytoarchitectural substrate of an equivocal dermoscopic pattern, but also of identifying characteristic confocal features useful for an accurate diagnosis to be searched within the blue region of a suspect lesion."

In the study, most of the false-positive results seen were in the Spitz nevi group, showing a blue hue in 15 out of 27 cases, nine of which had two or more RCM criteria that were suspect of a malignant melanoma.

"If the clinician combines dermoscopy and RCM observations on selected dermoscopic features, allowing a focus on characteristic features that are particularly useful for interpretation of that pattern and for diagnostic judgment, a much more accurate diagnosis of a given lesion can be met," Dr. Pellacani says.