Water-based acrylic marker for reflectance confocal microscopy lesion delineation

Dear Editor,

Reflectance confocal microscopy (RCM) is a noninvasive diagnostic tool with near-histologic resolution and high diagnostic accuracy. Most lesions are easily evaluated with a wide-probe RCM; however, assessment of large lesions, scars, ill-shaped lesions, and specific non-flat anatomical areas (e.g., nose, ear, genitals, and periocular) might be challenging.^1,2 In these scenarios handheld RCM is typically used, however, orientation is critical, and delineation is challenging. Margin mapping, for example, requires an exact one-to-one correlation with RCM findings.^1,3 Also, the biopsy for genetic material, or aiming the most representative area of a lesion for ex vivo histopathological analysis requires visual reference.^4,5 To overcome this, paper rings, paper tapes, metallic grids, plastic laminate sheet adapters, and metallic ink pens have been used, with some limitations (Table 1).^1,4,6–8 Specifically, metallic ink pen tends to smear with the motion of the probe as the immersion oil used for imaging dissolves the lipophilic ink.¹

TABLE 1.

Comparison between the most used methods for reflectance confocal microscopy delineation

Method	Pros	Cons
Paper tape1	• Maintains adequate imaging quality • Allows for dermoscopic correlation • Very low cost • Easily obtainable on any health care center • Great for large or ill-defined lesions • Safe for skin contact • Useful for large and irregular lesions	• Hand-made cuts and paper fibers are less precise • Narrower width only 1.27 cm • Peeled off the skin with the immersion oil • Delineation of more than one area of the lesion could be difficult • Curved lesions or areas are difficult to explore
Metallic grid5	• Maintains adequate imaging quality • Allows for dermoscopic correlation • Allows for easy delineation of more than one area of the lesion • Its design allows more accurate marks and lesion measures • Gives precise grid-like correlation between RCM-dermoscopy-histopathology • Safe for skin contact	• Requires design and specific manufacturing • Not easy to remove for reuse in the same lesion • Should be avoided in patients with nickel allergy • Expensive
Paper ring6	• Maintains adequate imaging quality • Allows for dermoscopic correlation • Different sizes and widths available per specific requirement • Great for small, well-defined lesions • Safe for skin contact • Rings at different sizes for optimal precision biopsies	• Requires specific design and specific manufacturing • Expensive • Not useful for large, ill-defined lesions • Not manufacturable worldwide
Metallic ink pen7	• Maintains adequate imaging quality • Allows for dermoscopic correlation • Allows easy delineation of more than one area of the lesion • Great for ill-defined lesions • Maintains its visibility in all skin levels of RCM • Safe for skin contact	• With handheld RCM movement the ink smears • Hard to remove from skin with saline solution or water • Signal is less intense than with paper-based methods or metallic grid
Adapter window8	• Maintains adequate imaging quality • Allows for dermoscopic correlation • Cheap • Easily manageable by the operator • Safe for skin contact	• Requires specific design • Hand-made manufacturing could create variations between users • Non-precise window (between 3 and 4 mm). • Only delineates one area of the lesion.
Water-based acrylic marker	• Maintains adequate imaging quality • Allows for dermoscopic correlation • Allows easy delineation of more than one area of the lesion • Can be combined with other methods: paper tape, metallic grid, and adapter window • Easily erasable with saline solution • Cheap • Safe for skin contact • Maintains its visibility in all skin levels of RCM • Useful for large and irregular lesions	• Should be avoided in patients with acrylates allergy • Not available in all health-care centers • Signal is less intense than with paper-based methods or metallic grid

Abbreviation: RCM, reflectance confocal microscopy.

SOLUTION

We demarcate lesions using a water-based acrylic paint marker (POSCA, Uni Mitsubishi pencil). We delineate the area with the pen, then apply the RCM immersion oil that ‘fixes' the ink to the tissue (Figure 1). Then, we image with either a wide probe or handheld RCM. The marker's ink is hyper-reflective when it is in focus and hypo-reflective when out of focus (Figure 1). It casts a hypo-reflective band in the underneath areas, recognizable up to 200–250 μm depth (Figure 1). Marker tips sizes are available between 0.7- and 15-mm width (we suggest 0.7 mm, for avoiding excessive marks). The ink is odorless and nontoxic when applied on the skin (MSDS compliant). The pen is widely available (on art shops or online searching “Posca markers”), quick-drying, and easily erasable with saline solution or water (Supporting Information: Video). We use this pen when doing handheld RCM to aid in the navigation of large lesions and for video-mosaicking (Figure 2).²

FIGURE 1.

Lesion demarcation using water-based acrylic paint marker (red arrow). RCM shows epidermis, dermo-epidermal junction, papillary dermis (at 40, 90, and 150 μm) with the pencil mark visible in all the layers (seen as hyperreflective on the superficial layers and hyporeflective on the deeper layers).

FIGURE 2.

RCM video-mosaicking using handheld images obtained with the water-based acrylic paint marker on healthy skin. The marker ink is visible as a hyperreflective line at this depth (arrows). RCM, reflectance confocal microscopy.

Supplementary Material

SUPPORTING INFORMATION

Additional supporting information can be found online in the Supporting Information section at the end of this article.