Keys To Diagnosing And Addressing Onychomatricoma

A 64-year-old male patient recently diagnosed with a movement disorder presents for evaluation of a dystrophic hallux nail. He denies any history of trauma to the nail but does relate experiencing intermittent pain to the toe. His primary care physician recommended an over-the-counter topical product, an antifungal, which the patient tried for a few months with no visible changes to the area. He wants to know if he has a fungal infection of the nail.

Upon examination, the nail is non-tender to palpation and has a banded yellow discoloration extending from the cuticle to the distal tip of the nail plate. Splinter hemorrhages are also present. Dermatoscopic examination revealed small circles in a honeycomb-like pattern in the nail plate that corresponded to the longitudinal discoloration when viewing the distal tip of the nail.

The practicing physician should be aware of this scenario. As it is commonly stated, and in my experience, 50 percent of nail dystrophy is onychomycosis, the other half is something else. In this case, the “something else” is an onychomatricoma. First described in 1992, onychomatricoma is a benign tumor of the nail matrix.¹ Although it occurs infrequently, one can easily mistake this condition for onychomycosis, due to its alteration of the nail plate and the lack of knowledge of its existence amongst clinicians.²

In general, subungual tumors are rare and difficult to diagnose due to the overlying nail plate obscuring their visualization. That said, benign nail tumors occur more frequently than malignant ones.¹ Onychomatricoma is the first described benign tumor of nail matrix origin.¹ Visually, one may confuse this entity for onychomycosis, onychogryphosis, nail psoriasis, melanonychia and a glomus tumor.¹ Beyond misdiagnosis as onychomycosis, other less frequent differential diagnoses for onychomatricoma include subungual keratoancanthoma, subungual squamous cell carcinoma, ungual Bowen’s disease, subungual exostosis and subungual warts.¹

Assessment for pain, drainage, nail plate destruction and discoloration are important when investigating these lesions. Often, a radiograph may allow the physician to discern the outline of a subungual exostosis or even an osteochondroma, with the digit in question isolated on the lateral view for best visualization.¹ With a subungual or periungual wart, the nail plate may become onycholytic with subungual thrombosed capillaries. Unlike other tumors that affect the nail plate indirectly by invading the matrix or the nail bed, onychomatricomas are unique in that they are tumors that produce nail plate substance while causing abnormalities in the nail plate at the same time.¹

Although it is unknown why these occur, onychomatricomas are distinct visually and histopathologically.² Four signs characteristic of this lesion are:²

• diffuse thickening of the nail plate of various widths;

• yellow or white discoloration accompanied by splinter hemorrhages;

• transverse overcurvature of the nail; and

• direct visualization of a filamentous tumor emanating from the matrix upon nail plate avulsion.²

Even though it is often yellow or white in color dorsally, one case in the literature described a rare, pigmented variant of onychomatricoma that one would easily misdiagnose as subungual melanoma.³ From a histological perspective, it is a fibroepithelial tumor that has digitations that extend into the nail plate.² One can view these digitations as “wormholes” with a dermatoscope at the distal tip of the nail which aids in a preliminary diagnosis in the office. This often originates from the ventral nail matrix (lunula).⁴ Even though the etiology is unknown, it is thought that trauma and onychomycosis may play a role in its development.⁴ No matter what the predisposing factor, complete excision of the tumor is curative.⁴

The most frequent digits in which onychomatricoma occurs are the thumb, index and middle finger of the dominant hand followed by the hallux.⁴ It can present in both sexes ranging from ages four to 72 years, with 48 years being the average.⁴ As with many suspected tumors, an ultrasound or magnetic resonance imaging (MRI) may help determine if a soft tissue tumor is present dorsal to the distal phalanx. Prior to ordering imaging, I use a dermatoscope in the office to evaluate all nails in question, as there are well-described characteristics that help me distinguish anything from distal subungual onychomycosis to an onychomatricoma. In my experience, onychomatricoma often exhibits longitudinal white parallel lines and splinter hemorrhages when viewing the dorsal nail plate with the dermatoscope, but it is inspection of the distal free edge of the nail plate that assists me the most in diagnosis. When viewing the distal edge of the nail plate, there is a honeycomb-like appearance that corresponds to the digitations from the nail matrix that ultimately create tunnels in the nail plate.⁵

Keys To Biopsy And Management Of Onychomatricoma

In my experience, biopsy of the lesion is confirmative, with total excision of the lesion being treatment of choice. However, an article by Stephen and colleagues shows that one way of obtaining that diagnosis prior to total excision is by using nail clippings.⁵ The clinician can obtain an ideal specimen for the histopathology lab by first cleansing the nail plate with an alcohol swab and ensuring there are no nail cosmetics or polish present. Then one debrides a specimen at least four mm in length, which ensures an adequate sample for processing, followed by placing the clipping in a formalin-filled container.⁵ If the clinician also wants to rule out dermatophyte presence, one can also obtain a sample of the subungual debris by using a thin, metal nail curette and scraping the nail bed and underside of the nail plate.⁵ Send this sample in dry packaging such as an empty specimen container, dermapack or dry keratin sample plastic bag. It is imperative to communicate with the histopathology lab that you wish to rule out an onychomatricoma with the clipping and the dry subungual debris is to determine the presence of onychomycosis.

Upon confirmation that the lesion is indeed an onychomatricoma, nail avulsion plus excision of the lesion occurs next. Nail avulsion to visualize the tumor is recommended, followed by total excision of the nail bed and nail matrix down to bone.⁴ Prior to the procedure, one should warn the patient during the consenting process that disruption of the

nail matrix will cause the nail width to decrease, and recurrence of the tumor is possible, but rare.⁴

In Summary

Circling back to the patient case mentioned at the beginning of this article, I discussed with the patient the most likely diagnosis of onychomatricoma and offered the treatment plan of excising the tumor. The patient was undergoing a clinical trial at the time for his movement disorder diagnosis and declined surgical intervention, choosing to watch and wait.

Given its rarity and lack of discussion outside the dermatology world, onychomatricoma is most likely the benign tumor you have not encountered at a medical conference or learned in medical school. However, it is an important differential diagnosis as this condition is easily misdiagnosed as onychomycosis. It demonstrates the importance of incorporating laboratory testing and/or dermoscopy in addition to visual inspection. As stated previously, 50 percent of nail dystrophy seen in the office is not onychomycosis, so a clinician should not always expect to see a positive fungal test result. It also encourages clinicians to not always look down at a nail, but to inspect the distal edge of the nail, as in this case there is a distinct, visualizable entity that can lead to a diagnosis. 

Dr. Vlahovic is a Clinical Professor in the Department of Podiatric Medicine at the Temple University School of Podiatric Medicine in Philadelphia.

1. Haneke E, Franken J. Onychomatricoma. Dermatol Surg. 1995;21(11):984-987.

2. Morales-Cardona CA, Luque-Acevedo AA, Bermudez-Bula LF. Onychomatricoma: an often misdiagnosed tumor of the nails. Cutis. 2015;96(2):121-124.

3. Isales MC, Haugh AM, Bubley J, et al. Pigmented onychomatricoma: a rare mimic of subungual melanoma. Clin Exp Dermatol. 2018;43(5):623– 626.

4. Romero LS, Park H, Shoaee N, et al. Onychomatricoma presenting as a dystrophic right great toenail: case report and review. Cureus. 2020;12(5):e7946.

5. Stephen S, Tosti A, Rubin AI. Diagnostic applications of nail clippings. Dermatol Clin. 2015;33:289–301.