Ungual Fibrokeratoma
Acquired ungual fibrokeratoma (AUFK) — called acquired digital fibrokeratoma (ADFK) when it appears on the fingertip — is a rare, benign fibroepithelial tumor of the nail unit. It arises from the dermal connective tissue around the nail (periungual) or beneath it (subungual).
AUFK is not inherited. It is a reactive overgrowth of fibrous tissue following repetitive microtrauma or long-standing mechanical pressure, which drives abnormal proliferation of dermal fibroblasts.
- Histopathology:
- Epidermis: marked hyperkeratosis and thickening of the spinous layer (acanthosis). The most characteristic feature is the epidermis dipping down around the base of the lesion to form a surrounding keratin rim (epidermal collar or collarette).
- Dermis: thick, densely packed collagen bundles running parallel to the long axis of the lesion.
- Vessels and nerves: small dilated capillaries run along the axis of the lesion. The tumor contains no nerve fibers or sweat glands.
- Immunohistochemistry (IHC):
- The fibroblasts in AUFK stain strongly for CD34 and vimentin but are negative for S100, which helps separate it from nerve sheath tumors such as neurofibroma or schwannoma.
- How It Deforms the Nail Plate:
- When the lesion grows from the proximal nail fold, its tip protrudes outward while its base pushes down directly on the nail matrix.
- This pressure disrupts normal keratinization in the matrix, so a deep longitudinal groove forms in the nail plate as it grows out.
- If the lesion sits in the nail bed (subungual), it lifts the nail plate and causes localized separation (onycholysis).
Because it looks like a raised horny growth beside the nail, ungual fibrokeratoma is most often mistaken for a periungual wart (verruca vulgaris). Treating it the wrong way — superficial electrocautery, acid paints or surface CO2 laser — only burns off the tip and leaves the dermal base behind, so the lesion usually comes back and the matrix scarring gets worse. At Haute-Derma, onychoscopy to reveal the epidermal collar combined with microsurgical removal of the entire base is our standard approach for clearing this lesion completely.
Clinical Features and Digital Onychoscopy Findings
Ungual fibrokeratomas grow very slowly and are painless unless pressed on by tight shoes or knocked.
Three Classic Clinical Variants
- Type I: finger-like or rod-shaped variant: a small cylindrical or finger-shaped growth projecting from the nail fold, with a rough keratotic surface and a clearly visible keratin collar at its base.
- Type II: dome-shaped variant: a rounded, dome-like swelling with a smooth or slightly bumpy surface and firm, springy tissue.
- Type III: flat or subungual variant: a flattened lesion squeezed between the nail bed and nail plate, which arches the plate upward or splits it.
Digital Onychoscopy (Nail Dermoscopy) Signs
- Sides and tip of the lesion (exophytic component):
- A pale pink or milky white central mass reflecting the dense collagen stroma.
- Scattered red dots or linear vessels running along the body of the lesion.
- NO black dots (thrombosed capillaries) — the key sign that helps rule out a wart (verruca).
- Base of the lesion (the diagnostic clue):
- A clearly visible epidermal collar (collarette): a whitish band of keratin wrapping around the base where it meets normal skin.
Differential Diagnosis
| Condition | Key distinguishing features |
|---|---|
| Koenen tumor | Multiple periungual tumors on several digits, with other signs of tuberous sclerosis (ash-leaf hypopigmented macules, facial angiofibromas). |
| Periungual wart (verruca vulgaris) | Rough, cauliflower-like surface with black dots (thrombosed vessels); caused by HPV. |
| Supernumerary digit | Usually present from birth, at the base of the little finger, and rich in nerve fibers. |
| Glomus tumor | Very painful (especially with cold or a light knock), with a bluish or purple spot under the nail. |
| Squamous cell carcinoma (SCC) | Ulcerated, oozing surface, fast growth and progressive destruction of the nail. |
Diagnosis, Biopsy and Nail-Sparing Microsurgical Excision at Haute-Derma
At Haute-Derma, patients with a periungual lesion suspected to be an ungual fibrokeratoma are managed under our microsurgical root-excision and matrix-repair pathway (Haute-Derma AUFK Protocol):
Onychoscopy and High-Frequency Ultrasound (50 MHz)
- High-resolution onychoscopy: confirms the epidermal collar at the base and the absence of the thrombosed black dots typical of HPV.
- High-frequency ultrasound (50 MHz): shows how deeply the base extends toward the matrix or the periosteum, so the surgeon can map the incision precisely.
Microsurgical Root Excision (En Bloc Excision Down to the Periosteum)
- Digital block with 2% lidocaine without epinephrine.
- The proximal nail fold is opened as an eponychial flap to fully expose the base attached to the matrix.
- En bloc resection: using a microsurgical blade, the entire lesion is removed together with its dermal base and epidermal collar, down to the periosteum. Removing the whole base is the deciding factor in keeping the recurrence risk as low as possible.
Microsurgical Matrix Repair and Reconstruction
- The matrix surface is repaired flat and smooth with ultra-fine 8-0 microsurgical sutures (absorbable Monocryl or Ethilon).
- The proximal nail fold is laid back and a splint is placed to protect the nail bed.
Aftercare and Histopathology
- The specimen is sent for H&E and CD34 staining to confirm the diagnosis.
- An HPCH polymer film combined with LLLT (630 nm) helps the new nail plate grow out without the old groove over 4–6 months.
