What is the role of confocal microscopy in melanoma diagnosis?
Reflectance confocal microscopy
In vivo reflectance confocal microscopy (RCM) is a non-invasive technique that allows examination of the skin with cellular resolution. A systematic literature search up to 24 December 2015 identified a total of 21 studies involving 3108 patients with a total of 3602 lesions included in the per-lesion analysis: The pooled results for sensitivity and specificity were 93.6% (95% CI: 0.92-0.95) and 82.7% (95% CI: 0.81-0.84) respectively for the diagnosis of malignant lesions. Positive likelihood ratio and negative likelihood ratio were 5.84 (95% CI: 4.27-7.98) and 0.08 (95% CI: 0.07-0.10) respectively. Subgroup analysis showed that RCM had a sensitivity of 92.7% (95% CI: 0.90-0.95) and a specificity of 78.3% (95% CI: 0.76-0.81) for detecting melanoma. A systematic review by the Cochrane Collaboration compared the diagnostic accuracy of RCM and dermoscopy for cutaneous melanoma; reviewing 19 study cohorts (up to August 2016) with 2838 lesions (including 658 with melanoma); this provided 67 datasets for RCM and 7 for dermoscopy. The meta-analysis found RCM to be more accurate than dermoscopy in studies of participants with any lesion suspicious for melanoma and in participants with lesions that were more difficult to diagnose (equivocal lesion populations). For example, assuming a fixed sensitivity of 90% for both tests, specificities were 82% for RCM and 42% for dermoscopy for any lesion suspicious for melanoma (9 RCM datasets; 1452 lesions and 370 melanomas). The authors conclude that RCM may reduce the number of people receiving unnecessary surgery by up to three-quarters compared to dermoscopy. Selective participant recruitment, lack of blinding of the reference test to the RCM result, and differential verification were limitations. It was noted that studies may not have been representative of populations eligible for RCM, and test interpretation was often undertaken remotely from the patient and blinded to clinical information.
Lesions located on the head and neck, lesions in areas chronically damaged by sun-exposure, lesions dermoscopically demonstrating regression and amelanotic tumors represent the best indications for the use of RCM. It could be particularly useful to assess lentigo maligna margins.
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