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.
In cases of severe nail dystrophy, onychomycosis is a differential diagnosis of onychomatricoma, but these 2 conditions can also coexist.
Surgery is the recommended procedure for diagnostic confirmation as well as treatment of benign tumors of the nail matrix, like onychomatricoma.
Coexistence of onychomatricoma and onychomycosis on the same digit has been previously reported and is probably not infrequent. However, nail dermoscopy findings following only antifungal treatment are a novel insight.
Total nail avulsion is usually the preferred therapy when a single fingernail is affected by concomitant fungal infection and neoplasia. In cases of severe onychodystrophy, dividing the treatment in 2 steps might be a valuable approach. In this case, an oral antimycotic therapy allowed a less invasive surgical procedure.
Onychomatricoma is a benign and uncommon fibroepithelial tumor of the nail matrix. It was first described by Baran and Kint in 1992 . Onychomatricoma is suspected clinically and radiologically, but histopathology is mandatory for confirming diagnosis [2, 3]. Onychomycosis sometimes has similar clinical features and eventually leads to an initial misdiagnosis . Association between onychomatricoma and onychomycosis has been previously documented and is possibly not infrequent [4-8]. Presently, there are multiple therapeutic options for onychomycosis , but there is no standard treatment when there is coexisting onychomatricoma affecting the same fingernail [4-8].
A 52-year-old South American female referred painless nail thickening of her left index finger for 10 years. She denied any trauma or local symptoms. Physical examination showed nail dystrophy, chromonychia, increased transverse curvature, and nail plate thickening (Fig. 1a). Onychoscopy revealed multiple narrow cavities resembling ramified tunnels and subungual hyperkeratosis with a “ruin appearance” (Fig. 1b). Specimen obtained from the nail plate by curettage has shown the presence of septate hyphae, confirming the diagnosis of onychomycosis. Ultrasonographic evaluation exhibited a hypoechoic, oval, ill-defined lesion in the nail matrix with hyperechoic linear dots associated with nail plate thickening (Fig. 1c), providing diagnostic evidence of onychomatricoma. Onychomycosis with onychomatricoma has been the proposed diagnosis.
Onychomycosis was treated clinically for 6 months prior to nail surgery. Patient received oral terbinafine, 250 mg per day, daily for 6 months. Improvement of nail dystrophy, chromonychia, and hyperkeratosis was evident on physical examination (Fig. 2a). Dermoscopy exhibited proximal splinter hemorrhages and, at the distal margin, honeycomb-like cavities (Fig. 2b), typical features of onychomatricoma, whereas some prior characteristics of onychomycosis were not present anymore.
After the effective management of onychomycosis, onychodystrophy and nail thickening became much less severe. Therefore, surgery was performed in a more delicate and less invasive way compared with the complete nail avulsion, preserving the distal area of the plate. The tumor was excised, and upon histopathological analysis, the diagnosis of onychomatricoma was duly confirmed. Postoperative follow-up showed rapid recovery with complete nail plate regrowth in only 4 months.
Onychomatricoma is a rare neoplasm of the nail matrix with <200 reported cases [10-12]. Some of the major reasons for the limited number of reports are the relatively new histopathological diagnostic criteria and the lack of integrity of the specimens obtained and analyzed. It is classically an asymptomatic slow-growing tumor characterized by filamentous digitations arising from the matrix. Despite the fact that it is considered a tumor of the nail matrix, Perrin et al.  have suggested that some cases possibly arise from the ventral portion of the proximal nail fold.
Some authors have advocated that it mainly affects middle-aged women [10, 14]. However, it is debatable if there is a gender predilection [11, 15]. Ethnic predisposition to onychomatricoma is still unknown. Only cases of European descent were published during the first 7 years following its original description. Nevertheless, patients of Asian, African, and Hispanic origins have been recently reported [16-19]. Adults are affected predominantly, but not exclusively. Piraccini et al.  have published a case in a 4-year-old patient, which is still the only description in a child. Fingernails have been compromised in approximately three-quarters of the patients. However, if toenails are affected, the great toe is mainly involved . Occurrence is more frequent in the right side of the body and the fifth digits from both hands and feet are classically spared .
Clinically, 4 major signs are important for the diagnosis: longitudinal xanthonychia, proximal splinter hemorrhages, ungual hyperkeratosis, and transverse overcurvature. Besides that, villous digitations emerging from the nail matrix are a characteristic intraoperative finding [21, 22]. Atypical presentations have been reported for a considerable time. Raison-Peyron et al.  described in 1998 a case presenting with nail bleeding. Melanonychia, dorsal pterygium, and cutaneous horn have been later reported as rare presentations of onychomatricoma [6, 12, 21, 22]. In 2007, Estrada-Chevez et al.  described a new clinical variant: giant onychomatricoma. Following this original publication, at least 4 other cases have been reported to date [24-27].
Histopathologically, onychomatricoma is considered a fibroepithelial tumor composed of 2 portions: the proximal part (located beneath the proximal nailfold), which consists of the base of the pedunculated fibroepithelial lesion, and the distal portion, which is composed of multiple digitiform projections. The stroma of this tumor is arranged in 2 layers.
The superficial layer has a large number of fibroblasts, while the deeper is composed of dense collagen bundles and is less cellular. It also has a keratogenous zone that is important for the diagnosis but is frequently removed with the complete nail plate avulsion [21, 28].
Immunohistochemical study reveals that onychomatricoma and nail matrix have basically the same profile of expression of integrins and cytokeratins. Also, Merkel cells are usually present in both onychomatricoma and the normal matrix . CD34 is a traditional marker of fibroepithelial tumors, which is positive in onychomatricoma as well . However, expression of AE13 helps to distinguish it from other superficial fibrous neoplasms .
Imaging techniques are useful when onychomatricoma is suspected. The tumoral finger-like projections appear as hyperechoic linear dots on ultrasonography and as a Y-shaped structure with high-intensity signal on magnetic resonance imaging. Using in vivo confocal microscopy, assessment of the free edge of the nail plate reveals hyporeflective areas, which correspond to the channel-like structures .
The etiology of onychomatricoma has never been yet fully understood. Seeking a better comprehension of its underlying pathogenesis, in 2011, Cañueto et al.  published a genetic investigation in a patient. Testing revealed 34 genomic alterations, mainly affecting the chromosome 11. The cathepsin C and STIM-1 genes might be involved in its development .
Considering its clinical features, some cases are initially misdiagnosed and treated as onychomycosis. Lack of response to therapy sometimes raises the suspicion for a nail tumor . The topography affected might be a clue for either onychomycosis or onychomatricoma. Although it is possible that children have both fingernails and toenails infected in equivalent proportions, the toenail fungal infections are more frequent in adults. Notwithstanding this, it is important to mention that onychomatricomas are more prevalent in fingernails .
Few articles have reported the association of onychomycosis and onychomatricoma. To our knowledge, at least 5 adults and 1 child presented simultaneously both these conditions affecting the same digit. Probably, the presence of a neoplasm with villous projections is a predisposing factor for concomitant fungal invasion [4-8]. Some authors also consider that onychomycosis predisposes to onychomatricoma [8, 29]. However, considering the limited number of manuscripts documenting this association, it shall be considered the possibility of underdiagnosing and/or underreporting [4-8]. Dermatophytes are not the only pathogenic fungi responsible for infections in this context. Fayol et al.  and Mandrell  reported patients who have developed onychomycosis caused by hyaline and dematiaceous non-dermatophyte molds and concomitant onychomatricoma.
Chromonychia, nail plate thickening, and transverse overcurvature are elements usually present in onycho-matricoma [1, 3]. However, hyperkeratosis with a “ruin appearance” is a classic feature of onychomycosis [4, 31]. In our case, we hypothesized that her left pointer finger developed onychomatricoma and fungal infection. Ultrasonography and mycological examination supported this first thought. After taking terbinafine for 6 months, multiple characteristics have changed. Besides visualization of splinter hemorrhages and longitudinal parallel white lines, the most prominent alteration was the dermoscopic aspect of the subungual hyperkeratosis. There was a shift from a “ruin appearance” keratosis to a honeycomb-like pattern, typical findings of onychomycosis and onychomatricoma, respectively . Splinter hemorrhages and thickening of the nail plate are also frequently observed in cases of squamous cell carcinoma and onychopapilloma. However, longitudinal parallel white lines and well-demarcated edges seem to be more typical features of onychomatricoma. Dermoscopy of the free edge revealing nail pitting is another specific finding . In our case, these characteristics suggested onychomatricoma as the main diagnostic hypothesis, which was further histologically confirmed.
Although coexisting onychomatricoma and onychomycosis has been managed successfully with nail avulsion , systemic antifungal therapy before surgery has been previously documented and may be a valuable approach [5, 6]. In our case, a course of oral medication followed by partial proximal nail plate avulsion and excisional biopsy achieved a good clinical result. Treatment for onychomycosis has allowed a less aggressive surgical approach than complete avulsion and was achieved fast recovery and satisfactory cosmesis. When comparing the scenarios before and after antimycotic treatment, this case shows severe macroscopic and dermoscopic changes caused presumably by fungus in a nail affected by onychomatricoma.
Statement of Ethics
The patient has given a written consent to publish photos and details of the case.
Conflict of Interest Statement
The authors of this publication do not have any conflicts of interest to declare.
The authors did not receive any financial support.
T.N.G.J. had a critical role in writing and manuscript preparation as well as review of the literature. C.C. helped providing the radiological evaluation, critically reviewing the manuscript, and approving its final version. A.P.L. helped with a critical review of the manuscript and approval of its final version. R.C.N. had a critical role in propaedeutic and therapeutic conduct of the studied case, review of the literature, review of the manuscript, and approval of its final version.
This work was conducted at the Instituto de Dermatologia Professor Rubem David Azulay, Santa Casa de Misericórdia do Rio de Janeiro, Rio de Janeiro (RJ), Brazil.