Inner gray halo, a novel dermoscopic feature for the diagnosis of pigmented actinic keratosis: clues for the differential diagnosis with lentigo maligna.

Background: Pigmented actinic keratosis (PAK) is a frequent simulator of lentigo maligna (LM) on the face upon clinical and dermoscopic examination, leading to misdiagnosis and unnecessary excisions. LM and PAK share dermoscopic features, making it difficult to have a confident diagnosis of PAK only with current dermoscopic knowledge.

Objective: We sought to evaluate sensitivity, specificity, and interobserver reproducibility of a novel dermoscopic feature, inner gray halo (IGH), and establish its histopathological and confocal correlations.

Methods: Dermoscopists blinded to histopathological diagnosis evaluated 58 PAK and 21 LM for the presence of IGH and dermoscopy parameters. Areas exhibiting IGH were marked and imaged with reflectance confocal microscopy before sampling for histopathologic correlation. Reflectance confocal microscopy and transverse histologic sectioning were performed in 14 of 79 cases.

Results: IGH was present in 53 of 58 (94.1%) PAK and in 5 of 21 (23.8%) LM in our series (sensitivity 91.4%; specificity 71.4%; positive predictive value 89.8%). Interobserver agreement was excellent (Kappa 0.846). Through transverse and perpendicular histologic sections, a dermoscopic-histologic-confocal correlation of IGH was established.

Limitations: A larger test set is needed to further validate the use of IGH in the differential diagnosis of PAK and facial pigmented lesions.

Conclusion: IGH is a novel dermoscopic parameter useful for the differentiation of PAK from LM on the face.