Onychomatricoma: A Rare Case of Unguioblastic Fibroma of the Fingernail Associated With Trauma

Onychomatricoma (OM) is a rare benign neoplasm of the nail matrix. Even less common is its possible association with both trauma to the nail apparatus and onychomycosis. This case illustrates both of these findings.

Case Report
A 72-year-old white man presented to the dermatology clinic with a 26-year history of a thickened nail plate on the right third finger that had developed soon after a baseball injury. The patient reported that the nail was completely normal prior to the trauma. According to the patient, the distal aspect of the finger was directly hit by a baseball and subsequently was wrapped by the patient for a few weeks. The nail then turned black and eventually fell off. When the nail grew back, it appeared abnormal and in its current state. The patient stated the lesion was asymptomatic at the time of presentation.

Figure 1. Thickening, yellowdiscoloration, and transverseovercurvature of the nail plateon the right third finger withlongitudinal ridging.

Physical examination revealed thickening, yellow discoloration, and transverse overcurvature of the nail plate on the right third finger with longitudinal ridging (Figure 1). A culture of the nail plate grew Chaetomium species. Application of topical clotrimazole for 3 months followed by a 6-week course of oral terbinafine produced no improvement. The patient then consented to a nail matrix incisional biopsy 6 months after initial presentation. After a digital nerve block was administered and a tourniquet of the proximal digit was applied, a nail avulsion was performed. Subsequently, a 3-mm punch biopsy was taken of the clinically apparent tumor in the nail matrix.

On microscopic examination of the removed tissue, a benign mixed epithelial and stromal proliferative lesion was noted. The basaloid epithelium, lacking a granular layer, arose from the surface epithelial layer and formed a reticulated pattern extending into the stromal component, which was moderately cellular with spindle to fusiform nuclei dissecting between collagen bundles arranged in parallel arrays (Figure 2). The stromal component predominated over the epithelial component in this neoplasm. The nail was preserved in formalin and underwent hematoxylin and eosin staining. It was thickened and grossly showed filiform fibrous projections extending into the nail plate. Histologically, the nail displayed prominent oval clear channels. Periodic acid–Schiff staining was negative for fungal organisms.

A diagnosis of unguioblastic fibroma–type OM was made. After receiving the diagnosis, expected course, and treatment options, the patient was offered conservative surgical excision but preferred clinical monitoring. At his last visit (6 months after the biopsy), the nail plate distal to the biopsy site had thinning and improvement, while the nail plate distal to the matrix that was not removed continued to show thickening, yellow discoloration, overcurvature, and longitudinal ridging (Figure 3).

Figure 2. The basaloid epithelium arose from the surface epithelial layer and formed a reticulated pattern extending into the stromal component (A)(H&E, original magnification ×2). At higher magnification, the stromal component was moderately cellular with spindle to fusiform nuclei dissecting between collagen bundles arranged in parallel arrays (B)(H&E, original magnification ×10).

Figure 3. Six monthsfollowing the biopsy, thenail plate distal to to thebiopsy site had thinningand improvement, while thenail plate distal to the matrixthat was not removedcontinued to show thickening,yellow discoloration, andovercurvature with longitudinalridging.

Comment
Onychomatricoma is a rare tumor originating from the nail matrix. The tumor was first described by Baran and Kint¹ in 1992 using the term onychomatrixoma, but later the term onychomatricoma became more widely used.² Onychomatricomas are more common in adults (mean age, 48 years) and white individuals with no gender predilection.^3,4 Fingernail involvement is twice as common as toenail involvement.³ Onychomatricoma is the only tumor that actively produces a nail plate.⁴

Clinically, OM presents with yellow discoloration along the entire nail plate and proximal splinter hemorrhages. It has a tendency toward transverse overcurvature of the nail plate with prominent longitudinal ridging.⁴ Trauma has been associated in at least 3 cases reported in the literature, though the association was sometimes weak.^3,4 Xanthonychia and onychodystrophy of the nail are common.³ Pterygium, melanonychia, nail bleeding, and cutaneous horns have been reported but are rare.^3-5 The tumor typically is painless with no radiographic bone involvement.³ Onychomycosis can be present,³ which may either be a predisposing factor for the tumor or secondary due to the deformed nail plate.⁴

When the nail plate is avulsed and the proximal nail fold is turned back, the matrix tumor is exposed. This polypoid and filiform tumor has characteristic fingerlike fibrokeratogenous projections extending from the nail matrix into the nail plate.³