Subungual squamous cell carcinoma
Periungual SCC; HPV-associated digital SCC; Bowen disease of the nail unit
Subungual squamous cell carcinoma is an under-recognised cause of chronic nail-unit symptoms — persistent paronychia, onycholysis, longitudinal erythronychia or nail-bed dystrophy — that has often been treated for months or years as fungal infection, chronic paronychia or trauma before the correct diagnosis is reached. The fingers are far more commonly affected than the toes, and high-risk HPV (predominantly HPV-16) is implicated in many cases, particularly in patients with anogenital HPV-related disease. Any chronic nail change without a clear alternative diagnosis warrants nail-unit biopsy. Mohs micrographic surgery is the treatment of choice for digit-preservation; amputation is reserved for invasive disease with bone involvement.
Clinical features
- Chronic persistent paronychia, onycholysis, longitudinal erythronychia, nail-plate dystrophy or non-healing nail-bed ulcer.
- Verrucous or hyperkeratotic periungual change in some cases.
- Most commonly affects fingers — particularly thumb and index — though toe involvement occurs.
- Median age 50–70; both sexes; male predominance in some series.
- HPV-16 detected in a substantial proportion of cases; consider co-existing or prior anogenital HPV-related disease.
- Typically a long history (often > 12 months) of mistreatment for fungal or inflammatory disease before diagnosis.
Investigation
- Biopsy is essential — punch biopsy of the nail-bed or matrix after nail-plate removal, longitudinal nail biopsy for matrix lesions, or excisional biopsy for circumscribed lesions.
- Histology — in-situ disease (Bowen disease of the nail unit) or invasive SCC.
- HPV typing on biopsy material in selected cases.
- Plain radiograph of the digit to exclude bone invasion; MRI for soft-tissue extent if invasive.
- Examine the anogenital area for synchronous HPV-related disease.
Management
- In-situ disease / superficial invasion — Mohs micrographic surgery is the digit-preserving treatment of choice; high cure rates and minimal functional loss.
- Wide local excision is an alternative where Mohs is not available, with margin assessment.
- Invasive disease with bone involvement — distal-phalangeal amputation, often at the DIP joint, with histological margin assessment.
- Imaging-defined deep invasion warrants MDT discussion and consideration of adjuvant RT.
- Lymph-node assessment is rarely required for early disease; advanced disease follows the cSCC pathway.
- Counselling — HPV vaccination consideration in patients with multifocal HPV disease, anogenital surveillance, smoking cessation.
Pitfalls and learning points
- Any non-healing nail-unit change > 3 months without microbiological confirmation of fungal/bacterial cause should be biopsied.
- HPV-related digital SCC is over-represented in patients with anogenital HPV disease — examine and counsel accordingly.
- Recurrence after non-Mohs excision is significant; specialist follow-up for 5 years is recommended.
- Distinguish from subungual melanoma (pigmented), subungual exostosis (bone), onychomatricoma, glomus tumour and chronic paronychia.
References
- Lecerf P et al. A retrospective study of squamous cell carcinoma of the nail unit. J Am Acad Dermatol; 2013.
- Riddel C, Rashid R, Thomas V. Ungual and periungual human papillomavirus-associated squamous cell carcinoma. J Am Acad Dermatol; 2011.
- Keohane SG et al. British Association of Dermatologists guidelines for the management of people with cutaneous squamous cell carcinoma 2020. Br J Dermatol. 2021;184(3):401-414.
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