Dermoscopy modalities yield varied results

October 1, 2007

Dermoscopy has become integral to identifying skin lesions and is an irreplaceable tool in the skin cancer screening armamentarium. Nonpolarized dermoscopy and the recently commercially available polarized dermoscopy yield overall similar images, but according to one expert, subtle differences exist. These differences may play a crucial role in confirming the diagnoses of lesions, such as dermatofibroma, basal cell carcinoma, seborrheic keratosis and melanoma.

New York - Different dermoscopic modalities are not created equal. Each type of dermoscopy has unique capabilities to evaluate the fine structures of skin lesions, allowing a more confident and precise diagnosis.

Ashfaq A. Marghoob, M.D., department of dermatology, Memorial Sloan Kettering Cancer Center, reports on a study that evaluated dermoscopic features and patterns of skin lesions by using conventional and polarized light dermoscopy (or cross-polarized dermoscopy).

The study included 90 patients with skin lesions that were imaged using conventional nonpolarized light contact dermoscopy (NPD), polarized light contact dermoscopy (PCD) and polarized light noncontact dermoscopy (PNCD). The skin lesions included 55 melanocytic lesions.

"We found that conventional direct contact dermoscopy and polarized dermoscopy were not equivalent in their assessment of skin lesions, but when used together, they provided complementary information, allowing for a clearer diagnosis," Dr. Marghoob says.

The dermoscopic nuances seen when using these three different techniques were significant and helpful to ensure a diagnosis of a given skin lesion that may have been ambiguous with the use of a single technique.

Unlike nonpolarized light dermoscopy, polarized light dermoscopy allows the visualization of deep skin structures beyond the stratum corneum without the necessity of a liquid interface or a direct skin contact with the instrument. The subtle differences seen, and especially the side-by-side comparison of dermoscopic images, can increase the clinical diagnostic accuracy as well as improve a physician's confidence in his or her clinical diagnosis.

"Polarized light helps one to see vessels and vascular blush much better than nonpolarized light. Thus, it may turn out that polarized light is the most sensitive form of dermoscopy to detect cutaneous malignancies," Dr. Marghoob says.

Nonpolarized light

Dr. Marghoob says nonpolarized light dermoscopy requires a liquid interface (e.g., 70 percent ethanol) and direct contact between the dermoscope and the skin. Here, the amount of light reflected, refracted and diffracted at the skin surface is reduced, allowing the physician to visualize the structures below the stratum corneum.

"Nonpolarized light helps one to see milia cysts much better than polarized light. This is important to help diagnose seborrheic keratosis. Polarized light will prevent the observer from recognizing milia cysts, leading to seborrheic keratoses being misdiagnosed as possible malignant melanoma (MM).

"Since there are thousands of seborrheic keratoses for every MM, the specificity for MM would end up being low. Thus, it is reasonable to assume that nonpolarized light will help increase the specificity of MM diagnosis by allowing the observer to recognize seborrheic keratosis," Dr. Marghoob says.

When examining a skin lesion and deciding on a type of dermoscopy, dermatologists should recognize the potential benefits and limitations inherent with each type.