Proliferating Onychomatricoma. Clinical, Dermoscopical, and Pathologic Features of Onychomatricoma New Variant Resembling Onycholemmal/Squamous Cell Carcinoma

Proliferating onychomatricoma is a new challenging variant of onychomatricoma that can clinically and histologically mimic squamous cell carcinoma/onycholemmal carcinoma. This is a retrospective case series study of the clinicopathologic and dermoscopic features of 6 patients with a pathologic diagnosis of proliferating onychomatricoma, which was conducted in the dermatology and dermatopathology departments of 2 university hospitals and a private nail's dermatology consultation. The clinical, histological, and immunohistochemical features and follow-up of 6 patients with proliferating onychomatricoma were analyzed; we compare our finding with 6 cases of conventional onychomatricoma. The female-to-male ratio was 1:1 with involvement of fingers in 4 and toe in 2. Among the symptoms were verrucous lesion simulating squamous cell carcinoma, nail thickening, periungual erythema, and pain; symptom duration ranged from 5 to 8 years. Clinical, dermoscopical en face free-margin view, and nail-clipping histologic findings reveal a nail wall-like pattern with pitting. Intraoperative, noncontact, polarizing, light dermoscopy was available in 1 case and showed the typical signs of onychomatricoma (OM). Histologically, all cases showed a well-differentiated, infiltrative, squamous, proliferative lesion exhibiting a lobulated and cystic pattern of growth in the dermis. Abrupt keratinization reminiscent of trichilemmal keratinization, but corresponding in fact to keratogenous spheres, was noted as well as a dysmaturative epithelial pattern. No atypical cytomorphological changes were found. Proliferating onychomatricoma is a new variant of onychomatricoma, which can be misdiagnosed as squamous cell carcinoma/onycholemmal carcinoma; its proper recognition may minimize morbidity associated with inappropriate treatment. Proliferating OM can be differentiated from conventional OM clinically by a free-edge wall-like pattern and on histology of nail clipping by the relatively small size of the cavities. Dermoscopic and nail clipping attributes as free-edge honeycomb-like cavities associated with conventional OM are well established and permit a diagnosis of OM without an invasive nail biopsy. The free-edge wall-like pattern is a distinct new dermoscopic and nail-clipping pattern that should raise for the others onychogenic neoplasms and prompt the clinician to obtain a biopsy specimen. In addition to proliferating OM, the differential diagnosis includes a micropapilliferum variant of OM, onychocytic matricoma, and onychocytic carcinoma.