Validation of dermoscopy as a real-time noninvasive diagnostic imaging technique for actinic keratosis. 
To validate dermoscopy as a real-time noninvasive diagnostic imaging technique for actinic keratosis (AK).  Prospective study to validate a diagnostic test.  Dermatology department of a tertiary university hospital in Fuenlabrada, Madrid, Spain.  A total of 178 patients with a clinical diagnosis of AK participated in the study.  An independent blinded comparison was performed between dermoscopy results and histopathological findings, the gold standard for the diagnosis of AK.  All the patients underwent both diagnostic tests.  One hundred seventy-eight lesions were evaluated.  The concordance between dermoscopy results and histopathological findings was 0.917.  The sensitivity of dermoscopy for the diagnosis of AK was 98.7%, with a specificity of 95.0%, a positive likelihood ratio of 19.74, and a negative likelihood ratio of 0.01.  A diagnostic algorithm that combined follicular openings and erythematous pseudonetwork demonstrated a sensitivity of 95.6% and a specificity of 95.0% for the diagnosis of AK.  The sensitivity and specificity of dermoscopy for the diagnosis of AK were high, as was the concordance between dermoscopy results and histopathological findings.  As a real-time noninvasive diagnostic imaging technique for AK, dermoscopy may be incorporated in the management of patients with these lesions.