Unusual Dermoscopic Patterns of Seborrheic Keratosis

Abstract

Background: Seborrheic keratoses (SKs) may sometimes mimic benign and malignant skin tumors, and a biopsy can be necessary in order to rule out malignancy. Methods: From the database of our pigmented lesion clinic, we evaluated the dermoscopic features of difficult-to-diagnose SKs that were biopsied between January 2010 and December 2014. Results: SKs represented 3.8% of all excised lesions (161/ 4,182). Specifically, 91 (56.5%) were excised to rule out melanoma, 63 (39.1%) to rule out squamous cell carcinoma and 7 (4.4%) to rule out basal cell carcinoma. The following 10 global dermoscopic patterns were identified: multicomponent (32; 19.9%); reticular (24; 14.9%), characterized by an irregular pigment network; bowenoid (21; 13.0%); hairpin (19; 11.8%); keratoacanthoma-like (16; 9.9%); blue-nevus-like (15; 9.3%); lichenoid (6; 3.7%); hyperkeratotic (6; 3.7%); clonal (5; 3.1%); spitzoid (5; 3.1%). Furthermore, 12 SKs (7.5%) were not included in any of such patterns (not classified). Conclusion: Our results are in line with previous studies highlighting the dermoscopic variability of SKs. Although excised SKs may be classified into 1 of 10 repetitive dermoscopic patterns, a biopsy remains mandatory for those that cannot be clearly differentiated from common skin malignancies.

The limitations of dermoscopy: false‐positive and false‐negative tumours

“…Milia‐like cysts, comedo‐like openings, brain‐like structures, fingerprinting‐like structures, sharp demarcation, moth‐eaten borders represent well‐known features highly suggestive of SK. However, some peculiar subtypes of the tumour often lack the aforementioned features and might escape recognition even after dermoscopic examination …”

“…However, some peculiar subtypes of the tumour often lack the aforementioned features and might escape recognition even after dermoscopic examination. 5 • For reticular SK and solar lentigo (SL), the presence of pigment network is known to represent the dermoscopic hallmark of melanocytic tumours, and for this reason, a reticular SK/SL might be misinterpreted as a naevus or as a melanoma, if the network is asymmetric in terms of pigment distribution. 6 As compared to melanocytic tumours, the network of SK/SL is composed of thinner lines and larger holes and ends abruptly at the periphery without fading out.…”

Dermoscopy–pathology relationship in seborrheic keratosis

“…Irritation or trauma may alter the dermoscopic changes in SK by the formation of a polymorphous vascular pattern, ulceration or crust. In addition to these dermoscopic findings indicative of malignancy, when abnormal keratinization becomes pronounced, the lesion is more likely to be SCC/keratoacanthoma . White circles, keratin and blood spots were reported to differentiate SCC/keratoacanthoma from SK and other raised non‐pigmented skin lesions by dermoscopy …”

“…In addition to these dermoscopic findings indicative of malignancy, when abnormal keratinization becomes pronounced, the lesion is more likely to be SCC/keratoacanthoma. 32 White circles, keratin and blood spots were reported to differentiate SCC/keratoacanthoma from SK and other raised non-pigmented skin lesions by dermoscopy. 33 BCC Dotted-, globule-or nested-like structures are not generally seen in SK lesions by dermoscopy.…”

Seborrhoeic keratosis imaging in high‐definition optical coherence tomography, with dermoscopic and reflectance confocal microscopic correlation

“…1,2 Therefore, its differentiation from other skin tumours, including melanoma, can sometimes prove challenging. 3 Several non-invasive skin imaging techniques have emerged in recent years aiming for a higher accuracy in in vivo diagnosis. These include dermoscopy, reflectance confocal microscopy (RCM) and highdefinition optical coherence tomography (HD-OCT).…”