Dermoscopic Evaluation of Seborrheic Keratosis Can Help Diagnose Melanoma

A new study has identified several characteristics that can help to detect seborrheic keratosis (SK)–like melanomas using dermoscopy, including the presence of the blue-black sign, pigment network, pseudopods or streaks, and/or a blue-white veil. Identification of these characteristics can help clinicians to recognize and diagnose these difficult melanoma cases. The results of the study were published in JAMA Dermatology.

“Many practitioners, even nondermatologists, remove typical looking SKs without the use of dermoscopy and without confirming the diagnosis with pathologic analysis,” wrote Cristina Carrera, MD, PhD, of the department of dermatology at the Hospital Clínic de Barcelona in Spain, and colleagues. “All lesions of patients with numerous SKs need to be assessed dermoscopically to increase the possibility of detecting the odd SK-like melanoma.”

SKs are commonly occurring skin neoplasms that are frequently treated without biopsy. However, studies have shown that a percentage of these neoplasms may, in fact, be melanomas. Dermoscopy can be used to help confirm the diagnosis of SK.

With this study, Carrera and colleagues sought to describe dermoscopic features of diagnosed melanoma for which the clinical differential diagnosis included SK. They used clinical and dermoscopic images of proven melanoma in 134 patients treated at 9 centers. Two dermoscopy-trained observers evaluated the clinical descriptions and 48 dermoscopic features of all the images and classified each as SK or not SK, without the prior knowledge that all the lesions were melanoma.

Of the cases examined, the majority (82.1%) had features that suggested melanoma. Among these features were pigment network (55.2%), blue-white veil (53.7%), globules and dots (50.7%), pseudopods or streaks (35.1%), and blue-black sign (32.3%). The observers considered the remaining 17.9% of cases to likely be SK. Several other dermoscopic features were associated with misdiagnosis, such as hairpin vessels, fingerprint-like structures, network-like structures, and fissures and ridges.

Looking at images from the entire sample, the mean total dermoscopy score (TDS) was 4.7, with a 7-point checklist score of 4.4. Using dermoscopy, the SK-like melanomas had a total dermoscopy score of only 4.2. According to the researchers, the study suggests that dermoscopic algorithms “may be inappropriate for the diagnosis of SK-like melanomas.”

“Although the mean (SD) TDS was 4.71 (1.6) and 7-point checklist score for the whole sample was 4.37 (2.3), these numbers would have missed 69 (51.5%) and 42 (31.3%) of the melanomas in our series, respectively,” the researchers wrote.

Presence of blue-white veil, pseudopods and streaks, and pigment network were the most helpful criteria in diagnosing SK-like melanomas. Specifically, blue-black sign was significantly associated with a correct diagnosis.

“The recognition of SK-like melanomas requires a careful analysis of all criteria, even if they are not immediately obvious. At first glance, the keratotic aspect of such tumors could induce a confident but false clinical diagnosis of SK,” the researchers wrote. “Our study, however, highlights that dermoscopic melanoma clues could be found in most of the cases we evaluated, allowing a correct diagnosis.”