IS NON-TRAUMATIC NAIL DYSTRPOPHY ONLY DUE TO CHRONIC ONYCHOMYCOSIS? THE ONYCHOMATRICOMA. CASE REPORT

INTRODUCTION

Among the causes of chronic non-traumatic nail dystrophy, an infection by a dermatophytic fungus is by far the most common. In common practice the treatment of nail dystrophy and chronic onychomycosis is undertaken by general practitioners or dermatologists. Onychomatricoma (OM) is a rare benign nail tumour of fibro-epithelial origin, described originally by Baran and Kint in 1992 as Onychomatrixoma.¹

In 1995, Hanekee and Fränken, based on histological aspects, proposed the term onychomatricoma, which has been most frequently used in the scientific literature since then.² Other quotes and nomenclature such as onychoblastoma, onychoblastic fibroma and atypical onychoblastic fibroma are currently found and based on histological basis.^3,4 It is considered a rare, premalignant lesion, also defined as a “post-traumatic” neoplasm.¹

It is a specific tumour of the nail apparatus, characterized by the presentation of fingerlike projections from the matrix, and it is the only tumour in which alterations of the nail plate are actively produced by the lesion.^1,2 Its slow growth and the absence of pain in most cases explain patient’s typical delay in seeking medical attention.

Since its first description, just over 40 cases have been reported. The majority of the scientific literature is focused on etiology, histological and clinical aspects, however the description of any surgical therapy is still missing. In this article we describe a case of a non-traumatic onychomatricoma, providing practical tools for a differential diagnosis from other more common conditions and giving technical tips for surgical reconstruction.

CASE REPORT

A 60 years old female was referred to our Unit with a painless nail dystrophy of the left middle finger with no previous trauma reported. Physical examination revealed a yellowish discoloration of the entire sterile matrix, associated with an abnormal thickness and dystrophic appearance (Fig.1). The skin of the perionychium appeared normal. No apparent mass was either palpable or painful on palpation. Neither sensory changes nor cold intolerance were detectable in the fingertip on the volar side. Previous unnecessary 2-month therapy with anti-fungal medicinal products (Itroconazole 400 mg daily) was ineffective. All previous fungal cultures were negative.

A T1-weighted MRI evaluation (Fig. 2) revealed a mass originating from the germinal matrix that was 7 x 6 mm wide, with low signal capture and resembling normal epidermis. Due to the presence of a proximal inflow and distal venous drainage with perforations in the nail plate, an excisional biopsy was mandatory.

Under axillary block and with pneumatic tourniquet at 250 mmHg, the yellowed nail plate with a transverse overcurvature was removed with a freer elevator (Ulrich Medical AG, St.Gallen, Switzerland). With the help of 3.5x magnification loupes, a solid greyish lesion involving the sterile matrix was identified and removed, leaving a free margin of normal nail bed. The cleavage plane between the pathologic and normal nail bed was differentiated by the different colour and texture.

To prevent an early closure of the nail fold and keratinization of the nail bed, a polypropylene sheet was used as a sterile fingernail substitute. The sheet was trimmed from a reservoir of a common infusion set reproducing the profile of the avulsed fingernail and thinned at the proximal edge to reduce thickness in order to ease the insertion into the eponychial fold. A small hole was then created in the center of the foil to allow blood drainage and it was fixed with a 3-0 Prolene (Ethicon, Somerville, NJ) cross-stich suture (Fig. 3).

The substitute was removed after 6 weeks providing a good protection of the nail bed during the healing period. The histological examination revealed a fibroepithelial tumour with vertical filiform projections (Fig. 4) and confirmed the complete tumour excision. The aesthetic result after 9 months was excellent with no signs of local recurrence (Fig. 5).

DISCUSSION

Onychomatricoma (OM) is a rare slow-growing benign fibro-epithelial tumour originating from the nail matrix, affecting the nail bed of fingers and toes, painless and associated with onychodystrophy. Baran and Kint described it originally in 1992 and clinical literature is still limited. OM affects mainly females (2.16:1) with a peak incidence around the age of 51,⁵ rarely affects children and has prevalence in Caucasians although one case has been described in an African heritage.⁶

Etiology of nail dystrophy is not fully understood but trauma and onychomycosis are considered the main predisposing factors.

The OM is a slow growing painless tumour characterized by onychodystrophy, yellow longitudinal bands of variable width, distal splinter haemorrhages, prominent longitudinal ridging associated with woodworm-like cavities, increased transverse curvature of the nail plate, pincer nail deformity, cutaneous horn, melanonychia, nail bleeding and pterygium. ¹ Radiographic imaging shows an involvement of the underlying bone and MR images include a Y-shaped appearance with holes transversally.

It can be differentiated from total dystrophic onychomycosis and the most common nail bed lesions mainly by the clinical appearance, radiological evaluation and the histological examination.^7,8 In onychomycosis the nail bed matrix and the entire thickness of the nail plate is involved. The nail plate invaded by the pathogenic fungus becomes so fragile that the nail simply breaks away. In glomus tumours the mass is painful and is usually associated with point tenderness, cold sensivity, nail ridging and purple or blue nail discoloration. MR features are intermediate-to-low signal on T1-weighted images, marked hyperintensity on T2-weighted images and strong enhancement after injection of gadolinium-based contrast material. On histopathology glomus tumour appears as endothelium-lined vascular spaces surrounded by round epithelioid cells that may take on a spindle form.⁷ Subungual exostoses are painful, rapidly growing masses with associated cosmetic deformity. Radiograph studies are often diagnostic demonstrating a trabecular bony overgrowth projecting from the dorsal or dorsomedial distal phalanx.⁷

Another tumour that could simulate the picture of OM is the extraskeletal chondroma because it involves the subungual region. It is a painless subungual mass, a benign nodule of cartilage that does not connect to underlying bone causing mild and severe nail deformity.⁷ On histopathology these lesions appear as well-circumscribed, lobulated masses of hyaline cartilage with variable cellularity and plump nuclei. Another lesion that should be differentiated from the OM is the fibro-osseous pseudotumour of the digit. It is a rare, ossifying lesion involving the subcutaneous tissues of digits presenting as painful, localized, polypoid, erythematous swellings that may be ulcerated and can affect the subungual region. Unlike all the aforementioned lesions, nail plate avulsion in onychomatricoma reveals typical finger-like projection originating from a villous tumour of the nail matrix.²

CONCLUSION

For the aforementioned reasons in spite of the rare occurrence of this benign neoplasm compared to other fungal infections we think that OM should be taken into consideration by hand surgeons dealing with non-traumatic nail dystrophies of uncertain origin to prevent recurrence and possible malignant evolution. Surgical excision with nail apparatus reconstruction provides a good aesthetic result.

Acknowledgements

We thank Dr. Leoni Parvex Sandra for the technical help in the histopathologic evaluation.

Declaration of interest: The authors report no conflict of interest. The authors alone are responsible for the content and writing of this article.

Corresponding author:

Stefano Lucchina M.D.

Locarno’s Regional Hospital – Hand Surgery Unit

Via all’Ospedale 1, 6600 Locarno

Switzerland

E-mail: info@drlucchina.com