Nail Pterygium
Nail pterygium (pterygium unguis) is abnormal fibrosis and scarring of the nail unit, in which the skin of the nail fold or hyponychium overgrows, advances and becomes firmly fused to the nail plate or nail bed. Depending on where it occurs, it takes two forms that differ completely in nature and cause: dorsal pterygium and ventral pterygium (pterygium inversum unguis).
How each form develops:
- Dorsal pterygium:
- It begins with inflammation that irreversibly destroys the cells of the nail matrix.
- Once the matrix stops working, new nail plate is no longer produced. With no keratin plate in between, the skin of the proximal nail fold (PNF) comes into direct contact with the nail bed beneath and fuses to it with scar tissue (synechia).
- Over time, a wing-shaped (V-shaped) band of skin extends from the proximal nail fold toward the free edge, splitting the nail plate into two separate halves or wiping it out completely (anonychia).
- Ventral pterygium (pterygium inversum unguis, PIU):
- It results from abnormal adhesion between the skin of the hyponychium, or the distal nail bed, and the underside of the nail plate.
- This adhesion obliterates the natural distal subungual groove. The hyponychial skin clings to the nail plate and is drawn forward toward the free edge, carrying many blood vessels and sensory nerves with it.
Main Causes
- Dorsal pterygium:
- Nail lichen planus: the leading cause of non-traumatic dorsal pterygium. A T-cell-mediated immune attack on the basal layer of the matrix causes irreversible scarring.
- Severe trauma or surgical complications: crush injuries to the matrix, severe burns, or poorly performed surgery that cuts through the matrix.
- Severe drug reactions and immune disorders: Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN) and graft-versus-host disease (GVHD).
- Ventral pterygium (PIU):
- Autoimmune connective tissue diseases: systemic sclerosis (the classic cause), systemic lupus erythematosus (SLE) and Buerger's disease.
- Chronic mechanical and chemical irritation: long-term use of nail polish, artificial nails or nail glue that irritates the hyponychium; congenital or inherited cases also occur.
Dorsal pterygium is treated as a nail emergency. Once the scar band has formed and fused completely to the nail bed, the matrix damage is irreversible and a new nail plate will never grow back. At Haute-Derma, when a patient shows signs of nail lichen planus (longitudinal ridging, loss of the eponychium, thinning of the nail plate), the doctor starts intralesional corticosteroid injections or systemic immunomodulating therapy straight away to shut down the inflammation and stop it from progressing to permanent dorsal pterygium.
Clinical Features and Classification
Clinical Features of Dorsal Pterygium
- Onset: loss of the eponychium/cuticle; the proximal nail fold becomes slightly atrophic or dusky red.
- Progression: the nail plate thins and develops deep longitudinal ridging, followed by a notch or gap in the middle of the plate.
- Established stage: a wing-shaped band of skin grows forward from the proximal nail fold over the nail bed. The nail plate is split in two (onychoclasis) or disappears entirely. The fused skin is flat, dry and tightly bound to the distal phalanx.
Clinical Features of Ventral Pterygium (PIU)
- Symptoms: patients complain of sharp pain and bleeding whenever they trim their fingernails or toenails with ordinary clippers.
- Free edge: the subungual groove is gone. The hyponychial skin stretches forward, clinging to the underside of the nail plate and protruding a few millimeters beyond its free edge.
- Vascular changes: dermoscopy of the hyponychium shows dilated capillary loops elongated in the direction of nail growth.
Dorsal vs. Ventral Pterygium: Key Differences
| Feature | Dorsal Pterygium | Ventral Pterygium (PIU) |
|---|---|---|
| Site of fusion | Proximal nail fold (PNF) fused to the nail bed | Hyponychium fused to the underside of the nail plate |
| Main causes | Nail lichen planus, matrix trauma, SJS/TEN | Systemic sclerosis (scleroderma), SLE, nail cosmetics |
| Effect on the nail plate | Plate is split, atrophied or lost | Plate keeps growing with a normal shape |
| Pain | Usually painless (except during acute inflammation) | Sharp pain and bleeding when clipping or trimming nails |
| Onychoscopy findings | V-shaped wing of skin, absent cuticle, matrix atrophy | Elongated hyponychium, lost distal groove, dilated hyponychial capillaries |
| Outlook for recovery | Very poor (irreversible matrix scarring) | Better (may regress if the underlying disease is treated) |
Diagnosis and Treatment at Haute-Derma
Diagnostic Assessment
- Onychoscopy (nail dermoscopy): we look for early signs of lichen planus (a violet band on the PNF, longitudinal ridges, loss of the cuticle) or of scleroderma (dilated nail fold capillaries, atrophy of the nail fold).
- Nail biopsy: recommended when early nail lichen planus is suspected, before a pterygium has formed, to confirm a lichenoid infiltrate in the matrix.
- Screening for systemic disease: ANA, anti-Scl-70 and anti-centromere antibody tests if a ventral pterygium suggests scleroderma or lupus.
Treating Dorsal Pterygium
- Pre-pterygium stage (acute, scarring not yet complete):
- Intralesional corticosteroid injections: triamcinolone acetonide (2.5–5 mg/ml) injected directly into the proximal nail fold/matrix area every 3–4 weeks for 3–6 months to suppress the lichenoid inflammation.
- Systemic treatment: short courses of oral corticosteroids, systemic retinoids (acitretin), or biologics/JAK inhibitors (tofacitinib) for severe, widespread nail lichen planus.
- Established dorsal pterygium (permanent scarring):
- Medical treatment no longer helps.
- Surgery: the fibrous scar band is released, the matrix is reconstructed or replaced with an autologous matrix graft, and an anti-adhesion barrier (silicone sheet or surgical gel film) is placed between the nail fold and nail bed for 3–4 weeks. Even so, the chance of a fully normal nail plate growing back is very low.
Managing Ventral Pterygium (PIU)
- Principle: protect the adherent skin underneath and never trim or forcibly peel it away.
- Local care:
- Patients are taught to angle the clippers outward and not cut deep into the adherent hyponychial skin, to avoid bleeding and infection.
- Apply a mild keratolytic and moisturizing cream (urea 10%, petrolatum) to the hyponychium daily.
- Stop all artificial nails, gel polish and acetone-based nail polish removers.
- Systemic treatment: control of scleroderma or systemic vascular disease under the care of a clinical immunology and allergy specialist.
