Causes of Monodactylous Onycholysis in a Diverse Patient Population

Abstract

Onycholysis, the separation of the nail plate from the underlying nail bed or lateral structures, is a common feature of various nail disorders. It is classified into primary (e.g., idiopathic) and secondary types, including traumatic, neoplastic, inflammatory, and infectious etiologies [1]. Monodactylous onycholysis (MDO) involving a single digit is particularly concerning for potential subungual malignancy, often necessitating diagnostic biopsy [2]. The patterns and causes of MDO remain poorly defined compared to those associated with polydactylous onycholysis Figure 1. Lack of awareness regarding the variety and complexity of nail disorders, particularly within diverse demographic groups, limits differential diagnoses, delays treatment, and can lead to dismissing severe conditions. This study aims to explore the demographic, clinical, and diagnostic trends specifically associated with MDO in our diverse patient population.

A single-center retrospective chart review from January 2017 to September 2024 identified patients who underwent nail procedures (diagnostic biopsy or therapeutic avulsion) for MDO. Exclusion criteria included polydactylous involvement, radiographic evidence of subungual exostosis, and insufficient clinical documentation. Except for retronychia, a clinical diagnosis was treated with avulsion, and all other diagnoses were biopsy-confirmed. Data collected included patient-reported race/ethnicity, gender, age during the procedure, and clinical/diagnostic information.

Among the 49 identified cases of MDO, the average patient age was 57 years. Most patients (59%, n = 29) identified as Hispanic/Latino, and 67% (n = 33) were female. Verruca vulgaris was the most common diagnosis (n = 11, 22%), followed by psoriasiform dermatitis (n = 9, 18%) and retronychia (n = 9, 18%), the latter affecting various digits, including fingers and toes. Four subungual squamous cell carcinoma (SCC) cases were identified, including three in situ and one invasive case (n = 4, 8%). Benign tumors, including onychopapilloma (n = 4, 8%), onychomatricoma (n = 1, 2%), and onychocytic matricoma (n = 1, 2%), were also identified. The remaining eight cases represented traumatic or mechanical onycholysis, supported by identifiable histological features and clinical history. The left great toe was the most frequently affected site (n = 15, 31%), followed by the right great toe (n = 8, 16%), while the bilateral thumbs were the most affected fingernails (n = 9). Notably, two squamous cell carcinoma (SCC) cases involved the left great toe, and one each involved the right second toe and left fourth fingernail.

To our knowledge, this study represents the largest cohort of patients with MDO analyzed to date. Importantly, our patient cohort is predominantly Hispanic/Latino, a demographic often underrepresented in the literature on nail disorders. This focus on a community of diverse racial backgrounds provides a unique opportunity to enhance our understanding of MDO across a varied patient population. The prominence of verruca vulgaris underscores the importance of early prevention and treatment strategies for human papillomavirus (HPV) infection in vulnerable populations [3]. The diversity of etiologies, particularly subungual SCC, emphasizes the need for routine examination and comprehensive diagnostic evaluation. The frequency of MDO with psoriasiform dermatitis aligns with research on inflammatory nail disorders in skin of color, where onycholysis was the most common nail bed finding in psoriasis [4]. Retronychia, the sole clinical diagnosis in this study, is often misdiagnosed as infectious paronychia or onychomycosis because of overlapping symptoms, including onycholysis, onychomadesis, and xanthonychia, leading to delayed treatment [5]. Moreover, the involvement of great toes and certain fingernails suggests potential functional and mechanical factors—such as footwear, repetitive stress, and occupational activities—may contribute to MDO localization.

The limitations of this study include its single-center design, small sample size, and restrictions on patients who underwent a diagnostic or therapeutic procedure. Despite these limitations, our findings provide novel insights into MDO and can help physicians make informed medical decisions for their patients.

Reviewed and approved by the University of Miami IRB, approval # 20220414.

The authors declare no conflicts of interest.