Reflectance Confocal Microscopy: An Elegant, Revolutionary Technique with Boundless Possibilities

by guest blogger Joshua Davyd Fox, University of Miami, MD class of 2016

 

At the 2015 American Academy of Dermatology Annual Meeting, I serendipitously discovered Reflectance Confocal Microscopy (RCM). I sat mesmerized, watching the presenters quickly flip through black-and-white mosaic images of in vivo skin at microscopic resolution in what may best be described as a fusion between radiology and dermatology. As a fly in a room filled with experts of a drastically underutilized technology, I felt as though I was witnessing something groundbreaking- the next evolution in dermatologic diagnosis since the revolutionary advent of dermoscopy.

 

Before I knew it, I was meeting a faculty member from my University to learn more about RCM and observe a case. The patient was a fair-skinned middle-aged woman with a dark brown macule on her buttock. The dermoscopic pattern was not diagnostic and would have required a biopsy.

 

RCM uses a laser as a source of monochromatic light. As the wavelength of the light increases in the near-infrared region (700-1400 nm), so does its depth of penetration into the skin; however, longer wavelengths have less lateral resolution.1 Thus, depending on the RCM application, the wavelength will vary based on the desired depth of penetration.

 

It is common to use an 830 nm diode laser on automatic image control, which adjusts the laser power to provide the best contrast (the range is 1-21mW and causes no tissue damage). A skin contact ring is affixed to the skin along with a drop of ultrasound jelly at the site of the lesion, and a small drop of a water-based gel is placed onto the objective lens that is in the housing of the skin-contact device.

 

The laser beam passes through a beam splitter, scanning and focusing optical lens, through the skin contact device and is focused on a couple of microns of skin. The light rays are refracted by various components of the skin such as membranes, melanosomes and keratohyalin granules based on their respective refractive indices. These refracted and reflected rays return to the direction of the detector (which is connected to the computer), though they are physically filtered by a small aperture that only allows the light rays originating from the focal point to strike the detector — hence, this is confocal microscopy. Similar to the contrast created by differing tissue radio-densities in x-ray imaging, in RCM the image depends upon the contrast that is created by the differing refractive indices of skin components. The water-based gel is used because it has a refractive index of 1.33, which is nearly equivalent to the 1.34 of the epidermis, thus eliminating artificial refraction.

 

One can choose how to display the captured images. For example, we captured 12 rows by 12 rows of 500-micron x 500-micron tiles that were combined to form a mosaic of a 6 mm x 6 mm field with resolution at the cellular level. We scanned multiple mosaic images of the lesion at various depths and magnifications and identified cells out of a tempestuous sea of black and white pixels.

 

Although confocal microscopy was developed in the 1950s it was not applied to skin imaging until the 1990s with Rajadhyaksha’s work.2 Today RCM is used clinically mainly in the diagnosis of skin cancer and corneal pathologies and in research in skin cancer, skin aging, laser treatment, pigment pathologies, melasma, UV-induced skin responses, wound healing, and conjunctival and corneal evaluation.3,4,5 In a recent study in the JAAD, handheld RCM was utilized in the evaluation of 47 eyelid tumors clinically suspicious of malignancy, and RCM had 100% sensitivity and 69.2% specificity in the diagnosis of malignant tumors of the eyelid.6 Even more impressive results were seen in a recent study in the American Journal of Ophthalmology, in which 30 patients with conjunctival tumors were correctly spared an excisional biopsy (based on at least 12 months of follow-up), and in all patients who did undergo excision (23), the authors found 100% RCM correlation to the histologic diagnosis.3

 

Our patient’s lesion that warranted a biopsy based on the physical exam and dermoscopy was found to be benign based on the RCM features. Nonetheless, the patient wished for the lesion to be excised, which was done in due time.

 

This leads to the question: should we ask patients prior to performing RCM if they want the lesion to be excised regardless, in which case RCM would not be performed? Perhaps there is a benefit to conducting RCM even in these patients, as the tool is still developing and, with each case, more information is added to fine-tune the technique? Are there applications of RCM which we have not even thought of yet? I’m sure there are.

 

Cost and reimbursement issues will likely play a large role in the utility of RCM outside of the university setting. The average device costs between $70,000-$100,000, and each patient requires approximately 10-20 minutes to image.

 

To me, RCM’s ability to image in vivo skin, real-time, at microscopic resolution makes it a beautifully revolutionary technique. Only time will tell on which applications RCM will be most focused.

 

Anyone who would like to learn the technique of reflectance confocal microscopy may be interested in attending a weekend course in November 2015, at the University of Miami School of Medicine and can email umcme@med.miami.edu, or call 305-243-6716 for more information.

 

Acknowledgments:
Thanks to Robert S. Kirsner MD PhD and Theresa Cao DO of the University of Miami who critically reviewed this work.

 

References:

  1. Calzavara-Pinton P, Longo C, Venturini M, Sala R, Pellacani G. Reflectance confocal microscopy for in vivo skin imaging. Photochemistry and photobiology. Nov-Dec 2008;84(6):1421-1430.
  2. Rajadhyaksha M, Grossman M, Esterowitz D, Webb RH, Anderson RR. In vivo confocal scanning laser microscopy of human skin: melanin provides strong contrast. The Journal of investigative dermatology. Jun 1995;104(6):946-952.
  3. Cinotti E, Perrot JL, Labeille B, et al. Handheld reflectance confocal microscopy for the diagnosis of conjunctival tumors. American journal of ophthalmology. Feb 2015;159(2):324-333 e321.
  4. Ulrich M, Lange-Asschenfeldt S. In vivo confocal microscopy in dermatology: from research to clinical application. Journal of biomedical optics. Jun 2013;18(6):061212.
  5. Marchini G, Mastropasqua L, Pedrotti E, Nubile M, Ciancaglini M, Sbabo A. Deep lamellar keratoplasty by intracorneal dissection: a prospective clinical and confocal microscopic study. Ophthalmology. Aug 2006;113(8):1289-1300.
  6. Cinotti E, Perrot JL, Campolmi N, et al. The role of in vivo confocal microscopy in the diagnosis of eyelid margin tumors: 47 cases. Journal of the American Academy of Dermatology. Nov 2014;71(5):912-918 e912.

 

 

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