Onychocytic cysts are uncommon, typically asymptomatic nail bed lesions, often detected incidentally in biopsies or excisions.1,2 They can present with pachyonychia, onycholysis, hyperkeratosis, or nail dystrophy, making them difficult to distinguish from other neoplasms.1
We present a rare case of onycholemmal cysts presenting as longitudinal leukonychia and review its differential diagnoses.
A 36-year-old woman from Bogotá, Colombia, presented with a 10-year history of a right thumb nail lesion, occasionally associated with mild pain. She had no history of trauma, prior treatments, or relevant medical conditions. Examination revealed longitudinal leukonychia reaching the lunula, V-shaped onycholysis, and a distal fissure (Fig. 1). Dermoscopy of the free edge showed subtle subungual hyperkeratosis (Fig. 2), initially suggesting onychopapilloma. Due to persistent symptoms, surgical intervention was performed. Following nail plate avulsion, the nail bed appeared normal, while intraoperative dermoscopy revealed faint yellowish globules (Fig. 2). A longitudinal biopsy uncovered firm subungual tissue. Histopathology demonstrated mild acanthosis of the nail bed epithelium and multiple small onycholemmal cysts in the dermis (Fig. 3).
Longitudinal leukonychia can result from benign, malignant, or inflammatory nail disorders (Table 1). We report the first case of onycholemmal cysts presenting as longitudinal leukonychia.1,2 Clinically, these cysts display variable features, including nail plate ridging, subungual hyperkeratosis, digital clubbing, onycholysis, or pincer nail deformity.1,2 Their pathogenesis remains unclear: Samman (1959) suggested they result from epidermal implantation after trauma;3 in patients with clubbing, a dermal fibroblast proliferation has also been suggested.2 They likely originate from the squamous epithelium of the distal nail bed at the isthmus transition zone. Histologically, onycholemmal cysts are lined by keratinized stratified squamous epithelium lacking a granular layer, with laminated eosinophilic keratin and an eosinophilic cuticle resembling the outer root sheath of hair follicles.1–3
Differential diagnoses of longitudinal leukonychia in one or multiple digits: clinical and histopathological characteristics.1–10.
| Diagnosis | Clinical Characteristics | Histopathology |
|---|---|---|
| Single Digit | ||
| Onychopapilloma | Leukonychia or erythronychia longitudinal, distal onycholysis, V-shaped fissures | Papillomatosis, acanthosis of the distal nail bed with premature keratinization, matrical metaplasia |
| Onychomatricoma | Longitudinal melanonychia or leukonychia, pachyonychia | Cystic spaces, hyperplasia of the matrix, monomorphic onychocytes |
| Onychocytic Matricoma | Longitudinal melanonychia or leukonychia, pachyonychia | Deep endokeratinization with concentric nests of prekeratogenous and keratogenous cells |
| Subungual Seborrheic Keratosis | Progressive leukonychia or melanonychia, distortion of the nail plate | Irregular hyperplasia of basaloid cells forming eosinophilic whorls |
| Squamous Cell Carcinoma | Leukonychia or erythronychia, distal onycholysis, pain | Epidermal dysplasia, atypical keratinocytes |
| Chronic Trauma | Leukonychia, usually in the hallux | Hyperkeratosis, irregular acanthosis, spongiosis, parakeratosis |
| Multiple Digits | ||
| Darier Disease | Leukonychia or erythronychia, “candy cane” nails, V-shaped nicks | Suprabasal acantholysis, dyskeratosis, hyperkeratosis, parakeratosis, epithelial hyperplasia of the matrix (white bands), matrix thinning (red bands) |
| Onychomicosis | Pseudo-leukonychia characterized by white or yellowish irregular streaks | Hyperkeratosis, parakeratosis, intrakeratonic neutrophils, PAS positive for fungal elements |
Management lacks standardized guidelines.1,2 Biopsy is diagnostic and therapeutic, allowing partial or complete excision.1 Recognizing underlying causes is essential, as leukonychia may occur in diverse contexts. This observation prompted a review of the potential causes of longitudinal leukonychia and its differential diagnosis. The pattern ‒ localized versus multifocal ‒ guides the differential diagnosis (Table 1).
Single-digit leukonychiaLocalized tumors or trauma are the main considerations. Benign tumors such as onychopapilloma may present as longitudinal erythronychia or, less commonly, as leukonychia or melanonychia, often accompanied by distal onycholysis, V-shaped fissures, or splinter hemorrhages. Histopathology typically shows papillomatosis, acanthosis of the distal nail bed, premature keratinization, and matrix metaplasia.4,5
Onychomatricoma and onychocytic matricoma ‒ benign nail matrix tumors ‒ can manifest with pachyonychia, longitudinal melanonychia, or, occasionally, leukonychia. The former demonstrates cystic spaces and matrix hyperplasia with monomorphic onychocytes forming nests, whereas the latter shows endokeratinization in the deeper portion of the neoplasm and concentrically arranged nests of prekeratogenous and keratogenous cells.5,6
Nail unit seborrheic keratosis may produce longitudinal melanonychia or, less frequently, leukonychia with progressive band widening and nail plate distortion. Histologically, it exhibits irregular hyperplasia of the distal matrix and nail bed, with basaloid cells forming eosinophilic whorls.7,8
Malignant tumors, particularly squamous cell carcinoma, may also present as longitudinal apparent leukonychia with concurrent erythronychia, reflecting vascular alterations. Histopathology reveals epidermal disorganization, dyskeratosis, and atypical keratinocytes.2,5,6,9
Finally, chronic trauma, especially involving the hallux, may result in a solitary longitudinal white band. Histopathology shows hyperkeratosis, irregular acanthosis, spongiosis, and parakeratosis.5
Multiple-digit leukonychiaWhen multiple nails are affected, inflammatory or hereditary disorders should be considered. Darier disease presents with greasy papules and plaques, sometimes associated with ocular or neuropsychiatric involvement.10 Nail changes include leukonychia and erythronychia (“candy cane nails”), V-shaped notching, and subungual hyperkeratosis.5,10 Similar findings occur in Hailey-Hailey disease and in tuberous sclerosis complex.5 Infectious causes, such as onychomycosis, may produce pseudo-leukonychia characterized by irregular white or yellowish streaks.5
This case broadens the clinical spectrum of onycholemmal cysts, highlighting the need to consider them in the differential diagnosis of monodactylous longitudinal leukonychia.
Financial supportNone declared.
Research data availabilityDoes not apply.
Authors’ contributionsMaria Paula Muñoz Mc Causland: Approval of the final version of the manuscript; critical literature review; data collection, analysis and interpretation; effective participation in research orientation; intellectual participation in propaedeutic and/or therapeutic management of studied cases; manuscript critical review; preparation and writing of the manuscript; statistical analysis; study conception and planning.
Isabela Dorado Caycedo: Approval of the final version of the manuscript; critical literature review; data collection, analysis and interpretation; effective participation in research orientation; intellectual participation in propaedeutic and/or therapeutic management of studied cases; manuscript critical review; preparation and writing of the manuscript; statistical analysis; study conception and planning.
Annie Mariana Melendez: Critical literature review.
Juan Carlos López: Data collection, analysis and interpretation; intellectual participation in propaedeutic and/or therapeutic management of studied cases.
ORCID IDMaría Paula Muñoz Mc Causland: 0000-0001-7923-6670
Annie Mariana Meléndez: 0009-0003-5743-5224
Juan Carlos López Hiromi: 0000-0002-2974-2193
Isabela Dorado Caycedo: 0009-0006-0311-1269
Conflicts of interestNone declared.
Study conducted at the Centros Médicos Colsanitas, Bogotá, Colombia.
