Pigmented onychomatricoma: a rare mimic of subungual melanoma

A Review of the Histopathology of Nail Unit Tumors Including Selection of the Optimal Surgical Sampling

Background

A wide variety of tumors can affect the nail unit, with some commonly mistaken as inflammatory or infectious diseases. Obtaining an optimal sample for histopathologic evaluation requires understanding of nail unit anatomy as well as the histopathology of the suspected nail tumor.

Summary

This review discusses clinical and histopathologic features of a subset of benign and malignant nail tumors, including subungual melanoma, nail unit squamous cell carcinoma in situ, nail unit squamous cell carcinoma, onychomatricoma, onychopapilloma, onychocytic matricoma, and onychocytic carcinoma. Optimal surgical sampling techniques for each lesion are presented.

Key Messages

In summary, the clinical and histopathologic features of several common and rare nail unit tumors and the optimal sampling techniques for each lesion are presented in this manuscript. Knowledge of the clinical and histopathologic features of these tumors informs the surgical approach to them and will produce the best patient outcomes.

Differential diagnosis of pigmented nail lesions

The diagnosis of pigmented nail lesions is a concern for both general practitioners and dermatologists, due to the possibility of indicating nail melanoma. The origin of the dark pigmentation can be either melanocytic or non-melanocytic (fungi, bacteria, or blood), and clinical evaluation alone may not be sufficient for differentiation, requiring additional exams. Onychoscopy provides valuable information prior to biopsy. The causes of nail pigmentation will be described to aid in the differential diagnosis.

Pigmented Onychomatricoma Presenting as Pachymelanonychia Striata: A Case Report and Review of Literature

Introduction

Onychomatricoma is a fibroepithelial tumor derived from the nail matrix and onychodermis. Many clinical and histological variants have been described. Pigmented onychomatricoma is a rare variant which presents as longitudinal pachymelanonychia.

Case Presentation

We report the details of a 41-year-old female who presented with blackening and thickening involving more than half of the left middle fingernail for the past 10 years. Dorsal plate onychoscopy revealed longitudinal parallel white, gray, and black bands, while onychoscopy of the distal free edge demonstrated a thickened nail plate with "wood worm" cavities. The histopathological examination of the excised tumor revealed a pigmented onychomatricoma.

Conclusions

Onychomatricoma is one of the nail tumors presenting as pachyonychia striata apart from onychocytic matricoma and onychocytic carcinoma. A pigmented onychomatricoma may closely mimic fungal melanonychia, pigmented onychopapilloma, pigmented ungual Bowen's disease, and ungual melanoma. Noninvasive techniques like onychoscopy and imaging studies like ultrasonography and magnetic resonance imaging are helpful in differentiating it from pigmented ungual Bowen's disease and ungual melanoma, even though diagnostic confirmation requires an excisional biopsy.

Onychomatricoma with Onychomycosis: A Case Report and Review of the Literature

Onychomatricoma is a primary benign neoplasm of the nail matrix. Currently, a limited number of cases have been reported, so it is still considered a rare neoplasia. However, it is debatable if this condition is underdiagnosed and underreported. Onychomycosis is an important differential diagnosis of onychomatricoma, and sometimes, both these conditions may even coexist in the same nail. As the tumor grows, tissue microenvironment is more vulnerable to dermatophytes. Probably, the altered keratin appears to be susceptible to fungal invasion. Careful clinical assessment and dermoscopic evaluation help nailing the diagnosis. Usually, total nail avulsion is the preferred therapeutic approach when they coexist. Herein, we present a case of a middle-aged woman with onychomycosis and onychomatricoma affecting a single fingernail. The proposed therapy was oral terbinafine for 6 months followed by a conservative surgery. There were dramatic changes in dermoscopic features after fungal treatment, which, to our knowledge, have not been previously reported.

Pigmented onychomatricoma: A clinical simulator that could not mislead ultrasound

INTRODUCTION

Onychomatricoma is a rare subungual tumor composed of stroma and nail matrix-like epithelium. Only seven cases of the pigmented variant have been reported in the literature.

CASE REPORT

We present a 62-year-old male patient with a 2-years history of a single fingernail thickening, deformation, and hyperpigmentation. He had been treated for onychomycosis, without improvement. Due to the increasing hyperpigmentation, and to rule out tumoral entities, including melanoma, a color Doppler ultrasound examination of the nail was requested, which showed a hypoechoic tumor of the nail matrix and bed, with hyperechogenic linear images inside, suggesting the diagnosis of onychomatricoma. Onychectomy and partial matricectomy were performed. Histological evaluation confirmed the diagnosis of onychomatricoma. Discusion and conclusion: Histological evaluation is the gold standard for the diagnosis of onychomatricoma. However, ultrasonography represents an easily accessible, non-invasive diagnostic tool for the initial evaluation of these tumors, especially in unsuspected atypical clinical presentations.

Myxoid Onychomatricoma-A New Case

Onychomatricoma is a slow-growing, benign neoplasm of the nail matrix with several histological variants. With only 2 cases previously reported, the term "myxoid onychomatricoma" has been used by some authors to describe a rare variant, known to have a fibromixoid component. We present a case of a 51-year-old Caucasian woman with a 1-year history of thickening and discoloration of the right thumbnail, who was initially misdiagnosed as onychomycosis. After performing a magnetic resonance imaging that showed a tumor with several filamentous projections, an onychomatricoma was suspected and a total distal plaque avulsion was performed. Histology revealed a biphasic tumor with an epithelial component and a prominent myxoid stroma. Immunohistochemical staining was then used, confirming the diagnosis. Considering these findings, we believe that our case meets the diagnostic description of "myxoid onychomatricoma" and is, therefore, a new case of this rare histological variant.