First Step of 2-Step Dermoscopy Algorithm is Accurate and Specific
The 2-step dermoscopy algorithm provides a systematic approach to determining the most probable diagnosis after examination to guide the decision-making process to biopsy or not biopsy a skin lesion. The first step of the algorithm utilizes an 8-step criteria ladder to help classify lesions as either melanocytic or nonmelanocytic. If a lesion is classified as melanocytic, the second step of the algorithm further refines the type of lesion. There have been concerns that the accuracy of the first step (differentiating melanocytic from nonmelanocytic lesions) has a high sensitivity but a low specificity. Errors in the first step of the algorithm would render the second step irrelevant.
In a recent study published in JAMA Dermatology, authors conducted a retrospective study of all skin lesions evaluated via the 2-step dermoscopy algorithm and biopsied in a particular practice over a 10-year period. During the study period 9168 lesions were biopsied; 17.9% were biopsy-proven melanocytic and 82.1% were biopsy-proven nonmelanocytic. Based on these data, the sensitivity of the first step of the 2-step algorithm to identify a true melanocytic lesion was 85%, and the specificity to identify a true nonmelanocytic lesion was 94%. The diagnostic accuracy of the first step was 93%.
The algorithm serves a dual purpose of triage and diagnosis for detecting a suspicious skin lesion. The first step has been criticized by some for being complex and unreliable, especially with regard to classification errors. The authors argue that the primary intent of the 2-step algorithm is to guide the clinician in the biopsy decision-making process regarding a suspected skin lesion, with a secondary intent of improving the prebiopsy diagnostic precision. When there was a misclassification of lesions in the first step, the clinical diagnosis was incorrect but the management outcome remained unchanged and thus did not affect patient care.
The authors conclude that, “the algorithm helps toward maximizing the detection of skin cancer, while lowering the number of biopsies of benign lesions. Our results demonstrate that the first step of the 2-step dermoscopy algorithm is highly sensitive and specific and support its continued use.”
By: Wendy Meltzer, MPH
Adapted from the original article.
[image by Dennis Hill]