Introduction
Onycholemmal carcinoma is an extremely rare, often misdiagnosed, malignant tumor of the nail bed epithelium. It is a variant of subungual squamous cell carcinoma first described in 2004.1 With <20 cases described in the literature, onycholemmal carcinoma lacks standardized diagnostic and management guidelines. The tumor follows an indolent clinical course and typically presents as a slow-growing, discolored, warty, crusted, or ulcerative lesion of the nail bed.1, 2, 3 As it progresses, patients can develop pain, swelling, erythema, onycholysis, erythronychia, onychodystrophy, bleeding, and/or ulceration.4,5 Onycholemmal carcinoma is diagnostically challenging due to its histopathologic overlap with other nail bed tumors and the evolving understanding of its differentiation patterns. Most cases have historically been managed with distal digit amputation; however, here we present a case of a 67-year-old man treated with Mohs micrographic surgery who achieved favorable oncologic clearance without significant morbidity.3,5 This case report aimed to contribute to the understanding of the clinical and pathologic features of onycholemmal carcinoma and to discuss evolving treatment options that preserve digit function and aesthetics.
Case report
A 67-year-old man with a history of nonmelanoma skin cancer presented to the dermatology clinic for evaluation of a chronic, 10-year history of left thumbnail dystrophy. The patient previously tried treatment with oral fluconazole, but had no improvement. Physical examination demonstrated a dystrophic, yellow nail with medial onycholysis and a friable subungual mass (Fig 1). The patient underwent a biopsy of the mass, revealing an epithelial tumor with infiltrating islands of atypical squamous cells with foci of abrupt keratinization lacking a granular layer (Fig 2, A, B). Areas of dystrophic calcification were also noted. Staining was negative for p16; Ki-67 demonstrated a variable mitotic rate field to field being brisk in foci (Fig 2, C). These findings were consistent with an onycholemmal carcinoma. The patient was subsequently referred to Mohs micrographic surgery for excision, achieving negative margins after 2 layers. He remained disease-free at 6-month follow-up.
Fig 1.
Clinical examination of the left thumbnail demonstrates a dystrophic, yellow nail with medial onycholysis.
Fig 2.
Biopsy from nail bed. A, Hematoxylin-eosin stain. B, Lobulated and infiltrating islands of atypical squamous cells with foci of abrupt keratinization lacking granular layer and foci of dystrophic calcification. (C) Staining with Ki-67 showing variable mitotic rate field to field. (D) Frozen section obtained during Mohs micrographic surgery demonstrating irregular lobules of atypical squamous epithelium consistent with onycholemmal carcinoma (A, B, D, Hematoxylin-eosin stain; original magnifications: A, 20×; B, 40×; D, 4×.).
Discussion
Onycholemmal carcinoma is a rare malignant neoplasm of the nail bed epithelium, representing a distinct variant of subungual squamous cell carcinoma with abrupt keratinization that mimics trichilemmal keratinization. The current literature describes <20 cases, with most reports highlighting the diagnostic challenges due to its indolent clinical course and histopathologic overlap with other onychoma. Clinical features include chronic onycholysis, periungual erythema, pain, and slow progression that often leads to a delayed diagnosis.5 The time to diagnosis ranges from several months to years, with an average time of just <3 years.5
The differential diagnosis is broad and includes benign entities such as onycholemmal cyst and horn, both of which are derived from the nail bed epithelium, and onychomatricoma, derived from the nail matrix. Malignant entities to consider are squamous cell carcinoma in situ, conventional squamous cell carcinoma of the nail unit, and subungual melanoma. The diagnosis is primarily based on pathology. Histologically, onycholemmal carcinoma is characterized by atypical keratinocytes that display lobulated and infiltrative growth, differentiating it from benign lesions. The hallmark feature setting it apart from standard squamous cell carcinoma is abrupt trichilemmal keratinization devoid of a granular layer. This trichilemmal keratinization is similar to that of the hair follicle, although embryologically unrelated.5 Proliferative indices (Ki-67) also tend to be lower than in conventional squamous cell carcinoma.2,6
Historically, management has favored distal digit amputation, particularly in cases with phalangeal bony invasion. However, recent evidence supports the use of digit-sparing modalities such as Mohs micrographic surgery and radiation therapy for onycholemmal carcinoma, highlighting comparable efficacy with less morbidity. This is justified by the indolent course of these tumors and the absence of reported metastases, recurrence, or death in any cases to date.4,5
Onycholemmal carcinoma is an uncommon, low-grade malignancy of the nail bed. A nonspecific clinical presentation contributes to a delay in diagnosis. While the majority of cases to date have been treated with amputation of the affected digit, our case adds to the small, but growing evidence of successful outcomes with digit-preserving therapy.
Conflicts of interest
None disclosed.
Footnotes
Funding sources: None.
Patient consent: Authors contained written patient consent for use of their photographs and medical information to be published online and with the understanding that this information may be publicly available and discoverable via search engines.
IRB approval status: Not applicable.
References
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