The use of Reflectance Confocal Microscopy to diagnose Malignant Melanoma and Lentigo Maligna in the United Kingdom: A Prospective Observational Trial at a Single Centre

Background: Previous work with Reflectance Confocal Microscopy (RCM) imaging has shown high sensitivity and specificity for Malignant Melanoma (MM), but to date there have been no studies on a UK cohort.

Objectives: The study hypothesised that RCM could be used prospectively to accurately diagnose MM and lentigo maligna (LM) in a private UK secondary care, single clinician setting. The study assessed the potential for RCM to be used as a routine screening procedure.

Methods: 597 patients were recruited consecutively where MM or LM featured in the differential diagnosis after clinical examination. A sequential record was made of the clinical, dermoscopic, and RCM findings by a single dermatologist [HS] prior to biopsy. Imaging used the arm-mounted confocal microscope unless access was restricted and required the handheld probe. The likelihood of MM was scored for each modality, each diagnosis building on the last. Histology was assessed by a single blinded histopathologist [JJ].

Results: 734 lesions were included in the analysis, including 86 MM and LM with a median diameter of 7.0 mm. The benign to malignant ratio was 3 to 1 (non-melanocytic malignancies included) and 8.3 to 1 for MM and LM only. The sensitivity and specificity for MM and LM was 62.8% (95% CI 51.70% to 72.98%) and 63.2% (59.27% to 66.84%) for clinical examination; 91.9% (83.95% to 96.66%) and 42.1% (38.14% to 45.88%) for dermoscopy; 94.2% (86.95% to 98.09%) and 83.2% (79.91% to 85.84%) for RCM. For RCM, PPV was 42.4% (38.13% to 46.81%) and NPV was 99.1% (97.87% to 99.60%).

Conclusion: This study demonstrates that RCM can reliably diagnose MM and is fast enough to be integrated into UK pigmented lesion clinics by dermatologists trained in RCM. "Number needed to treat" dropped from 3.9 with clinical examination to 3.0 with dermoscopy to 1.3 with RCM.