When Are Single Reader Evaluations Insufficient in Teledermoscopic Assessments? Analyses of a Retrospective Cohort Study

<b>Background:</b> Teledermoscopy (TDS) emerges as an efficient tool for diagnosing skin lesions. In Sweden, double reading is the standard of care, but risk factors for misdiagnosis or mismanagement using single reader evaluations (SRE) are not well-studied. This study aimed to assess the accuracy of SRE compared with the gold standard in TDS. <b>Methods:</b> This retrospective cohort study involved 1,997 TDS referrals sent from general practitioners to dermatologists in Stockholm, Sweden, selected based on dermoscopic diagnoses. All referrals underwent double reader evaluations (DRE). Each case was reassessed by a single external assessor, blinded to the DRE result. Based on predefined rules, a gold standard for the most correct diagnosis was established. Diagnostic accuracy and risk factors for misdiagnosis were evaluated. The trial was registered on ClinicalTrials.gov (ID NCT05033678). <b>Results:</b> Primary diagnosis by SRE agreed with the gold standard on benign-malignant classification in 84% of cases. Discordance was linked to lower diagnostic confidence and more frequent recommendations for further intervention. SRE achieved a benign-malignant sensitivity and specificity of 84% (95% confidence interval: 81-87% and 82-86%, respectively). The risk of overdiagnosis increased 96 times when assessors reported being "very unconfident." Out of a total of 311 melanomas, melanoma <i>in situ</i>, lentigo maligna, and severely dysplastic nevi, 62 were not recognized in the SRE primary diagnosis. However, 50 of these misdiagnosed lesions were still recommended for accurate management. <b>Conclusions:</b> The confidence level of TDS assessors heavily influences diagnostic accuracy. Therefore, when diagnostic confidence is perceived as moderate or low, additional interventions should be considered.