Dermoscopic Variations of Seborrheic Keratosis: A Pictorial Atlas

The Wide Spectrum of SK Appearances

Seborrheic keratosis (SK) is one of the most common benign skin lesions encountered in dermatology practice. Its clinical and dermoscopic appearances can vary significantly, making it a diagnostic challenge for both novice and experienced dermatologists. The variability in color, size, and texture of SK lesions necessitates a comprehensive visual guide to aid in accurate identification. A dermatoscope with UV light can enhance the visualization of subtle dermoscopic features, particularly in pigmented or inflamed variants. In Hong Kong, where skin cancer awareness is increasing, the use of a dermoscope for dermatologist has become indispensable in differentiating SK from malignant lesions like melanoma.

The need for a visual atlas is underscored by the diverse morphological presentations of SK. Lesions can range from light tan to dark brown, with sizes varying from a few millimeters to several centimeters. Texture may be smooth, verrucous, or even fissured. The dermoscopic features of SK are equally diverse, including comedone-like openings (CLOs), milia-like cysts (MLCs), and fissures. A systematic approach to recognizing these variations can significantly improve diagnostic accuracy and reduce unnecessary biopsies.

Common Dermoscopic Patterns

The classic dermoscopic pattern of SK is characterized by the presence of CLOs, MLCs, and fissures. CLOs appear as round, yellowish or brownish structures, while MLCs are small, white or yellow cysts scattered throughout the lesion. Fissures are irregular, dark lines that crisscross the surface. These features are often easily identifiable with a dermoscope for dermatologist, especially when using polarized light.

The reticular pattern is another common presentation, particularly in darker-skinned individuals. This pattern features a network of brown lines resembling a honeycomb. The homogeneous pattern, on the other hand, is characterized by a uniform pigmentation without distinct structures. Both patterns can be visualized more clearly with a dermatoscope with UV light, which enhances contrast and detail.

Pigmented Seborrheic Keratosis

Pigmented variants of SK can mimic melanoma, making dermoscopic evaluation crucial. Key dermoscopic features include sharp borders, multiple colors (brown, black, gray), and the presence of CLOs or MLCs. However, some pigmented SKs may lack these classic features, leading to diagnostic uncertainty. In such cases, a dermoscope for dermatologist with advanced imaging capabilities can provide additional clues.

Differential diagnosis with melanoma is particularly important in regions like Hong Kong, where the incidence of skin cancer is rising. Illustrative images comparing pigmented SK and melanoma can serve as a valuable reference. For example, melanoma often exhibits irregular pigmentation, atypical network, and blue-white structures, which are absent in SK.

Irritated Seborrheic Keratosis

Irritated SK presents unique challenges due to its inflammatory changes. Dermoscopic signs of inflammation include erythema, scaling, and crusting. These features can obscure the classic dermoscopic features of SK, making it difficult to distinguish from other inflammatory or malignant lesions. A dermatoscope with UV light can help by highlighting underlying structures that may be obscured by surface changes.

The clinical implications of misdiagnosing irritated SK are significant. Unnecessary biopsies or treatments can be avoided with accurate dermoscopic evaluation. For instance, the presence of residual CLOs or MLCs amidst inflammation can confirm the diagnosis of SK.

Clonal Seborrheic Keratosis

Clonal SK is a rare variant characterized by nested melanocytes within the lesion. Dermoscopically, it appears as well-defined, round or oval, brown or black nests surrounded by typical SK features. The distinctive features of clonal SK can be visualized more clearly with a dermoscope for dermatologist, particularly when using non-polarized light.

Special Sites and Variations

SK can occur on various body sites, each with unique dermoscopic characteristics. On the face, SK often appears as small, flat lesions with a homogeneous pattern. On the trunk, larger, verrucous lesions with CLOs and MLCs are common. Extremities may exhibit a mix of patterns, including reticular and homogeneous. A dermatoscope with UV light can enhance the visualization of these site-specific variations.

Enhancing Dermoscopic Recognition

The benefits of a visual atlas for SK are manifold. It serves as a practical tool for dermatologists to improve diagnostic accuracy and confidence. In clinical practice, the ability to recognize the diverse dermoscopic features of SK can reduce unnecessary procedures and improve patient outcomes. The integration of advanced imaging tools like a dermoscope for dermatologist further enhances the utility of such atlases.