A Case of Clonal Seborrheic Keratosis with Characteristic Dermoscopic Features
Seborrheic keratosis (SK) is a common benign epidermal tumor that typically presents in middle-aged and elderly individuals. While most cases of SK are easily diagnosed based on their clinical and dermoscopic features, certain variants, such as clonal SK, can pose diagnostic challenges due to their atypical presentations. This article presents a detailed case of clonal SK, highlighting its clinical, dermoscopic, and histopathological characteristics, and discusses the diagnostic pitfalls associated with this rare variant.
Clinical Presentation
The patient, a 40-year-old woman, presented with a gradually enlarging red oval plaque on the lateral aspect of her left leg. The lesion had been present for four years and was characterized by a rough surface. Notably, there was no evidence of ulceration, crusting, exudation, or bleeding. Physical examination revealed a well-defined, red flat plaque measuring 1.5 cm × 1.0 cm in diameter. The lesion was of medium hardness and was non-tender. The patient reported no systemic abnormalities and denied any associated pain or itching.
Dermoscopic Examination
Dermoscopy, a non-invasive diagnostic tool, was employed to further evaluate the lesion. The dermoscopic examination revealed several key features: multiple brown globules, dotted and globular vessels on a red background, follicular keratotic plugs, and multiple milia-like cysts. The lesion also exhibited a sharply demarcated border. These findings, while suggestive of SK, were not entirely typical, particularly due to the presence of brown globules within the red background, which increased the diagnostic complexity.
Histopathological Findings
Following surgical removal, the specimen was sent for histopathological examination. The pathology revealed proliferative nests of basaloid cells containing melanin, along with hyperkeratosis and acanthosis. Additionally, follicular keratotic plugs and horn cysts were observed. The upper dermis contained some dilated capillaries. These histopathological features confirmed the diagnosis of clonal SK.
The histopathology of clonal SK differs from that of typical SK. In this case, the basaloid cells were gathered into nests within the thickened epidermis, clearly bounded by the surrounding cells. This histopathological phenomenon is known as intra-epidermal epithelioma of Borst-Jadassohn, which corresponds to the “brown globules” seen on dermoscopy. The Borst-Jadassohn appearance is a histopathologic feature that can be found in several conditions, including clonal SK, hydroacanthoma simplex, and Bowen’s disease. The presence of dilated capillaries in the upper dermis was reflected as dotted or globular vessels on dermoscopy.
Discussion
Clonal SK is a rare variant of SK that can present diagnostic challenges due to its atypical clinical and dermoscopic features. The most common dermoscopic characteristics of typical SK include comedo-like openings, sharply demarcated borders, milia-like cysts, and hairpin vessels. However, the dermoscopic manifestations of clonal SK may only partially overlap with these features, as seen in this case.
The distinct feature of brown globules within a red background, as observed in this patient, is not a typical finding in SK and can complicate the diagnostic process. Previous reports have described the dermoscopic clod pattern in clonal SK, which can resemble features seen in congenital nevi, Spitz nevi, and malignant melanoma. Additionally, the presence of numerous dotted and globular vessels, as seen in this case, is less commonly reported in clonal SK.
In some instances, clonal SK may exhibit large blue-gray ovoid nests on dermoscopy, a feature typically associated with basal cell carcinoma. This overlap in dermoscopic features can lead to misdiagnosis, highlighting the importance of histopathological confirmation in cases of clonal SK.
Conclusion
The peculiarity of clonal SK lies in its lack of characteristic manifestations of typical SK, both clinically and dermoscopically. This case underscores the importance of histopathological examination in achieving an accurate diagnosis and avoiding misdiagnosis. While dermoscopy is a valuable tool in the diagnosis of SK, its limitations in the context of clonal SK must be recognized. Clinicians should maintain a high index of suspicion for clonal SK in lesions that exhibit atypical dermoscopic features and should proceed with histopathological evaluation to confirm the diagnosis.
doi.org/10.1097/CM9.0000000000000630
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