SAN DIEGO — Confocal microscopy is a promising technology to improve the management of skin lesions, but it's not quite ready for prime time, according to Dr. Lawrence T. Wang.
"At this time, the technology is very expensive, costing several tens of thousand of dollars," said Dr. Wang of the division of dermatology at Scripps Clinic Rancho Bernardo in San Diego, Calif. "It is time consuming, requiring 5-10 minutes to thoroughly evaluate a single lesion. The process is labor intensive and would likely require a trained clinician to interpret the images."
Confocal microscopy is a high-resolution, painless imaging technique that reveals epidermal structures including cells, connective tissue, and blood vessels to a maximum depth of about 300 microns. The illumination source is typically a laser.
"Only one point in the tissue is acquired at a time, so two-dimensional or even three-dimensional images are generated by scanning the tissue," Dr. Wang said at a melanoma update sponsored by the Scripps Clinic.
Findings from two recent studies suggest confocal microscopy may be useful in helping to improve the diagnosis of melanoma in the clinical setting. In one study, researchers from Italy and Australia evaluated 351 melanocytic lesions that were suspicious for melanoma based on clinical history, sequential digital photography, or dermoscopy (J. Invest. Dermatol. 2007;127:2759-65). They evaluated each lesion with confocal microscopy prior to biopsy and classified the lesions as either benign or malignant according to an algorithm based on major and minor criteria. They found that confocal microscopy showed a sensitivity of 96% and a specificity of 52%.
In the second study, Canadian researchers evaluated 125 suspicious pigmented lesions by dermoscopy followed by confocal microscopy (Dermatology 2007;215:365-72). The lesions were selected based on a history of change or clinical appearance. They found that confocal microscopy showed a sensitivity of 97% and specificity of 83%. The higher specificity "is likely due to the study design," Dr. Wang commented. "The authors' dermoscopic evaluation influenced their subsequent confocal evaluation. The study was designed this way to mimic a realistic clinical application of confocal microscopy."
Larger clinical trials of the technology are currently under way.
In Dr. Wang's opinion, current benefits of confocal microscopy include the fact that it provides immediate, real time, in vivo images prior to biopsy, removing the need for tissue preservation, sectioning, or staining. "This type of technology can significantly minimize sampling error when incisional biopsies are done of large pigmented lesions," he said. "The images are microscopic, giving single cell resolution."
However, the in vivo imaging falls short of conventional histology, he said, noting that nuclear features such as chromatin patterns, nuclear contours, and nucleoli "cannot be evaluated by confocal microscopy."
He also pointed out that since the depth of confocal microscopy is limited to the reticular dermis, subsequent biopsy of suspicious lesions "will always be needed to obtain a Breslow depth for melanoma lesions."
At this point in time, one of the best clinical applications of the technology is for managing large, atypical pigmented lesions. "Lesions in cosmetically sensitive areas such as the face are prone to sampling errors when partial biopsies are done," Dr. Wang explained. "Confocal microscopy could be used to scan entire lesions and direct appropriate sampling biopsies."
Dr. Wang disclosed having no relevant conflicts of interest.