Pterygium unguis is characterized by an abnormal fusion of skin and nail. Derived from the Greek word for “wing,” the name describes the resulting wing-like or triangular scar formation. This process involves the skin of the nail matrix growing forward and adhering to the nail bed, resulting in a visible deformity.
Defining the Condition and Its Appearance
Pterygium unguis is fundamentally a scarring-sclerosing process that leads to the formation of a septum-like skin bridge within the nail unit. This scarring causes a permanent fusion between the skin and the underlying nail structures. It is often the irreversible end stage of a severe inflammatory or traumatic event affecting the nail matrix.
The condition is divided into two classifications based on the location of the fusion. Pterygium Dorsale, often called “true” pterygium unguis, is the dorsal type. In this type, the proximal nail fold fuses with the underlying matrix and nail bed.
This fusion results in a characteristic V-shaped or triangular scar that progresses distally toward the tip of the finger or toe. As the skin bridge advances, it splits the nail plate into two lateral segments, which progressively decrease in size. In severe cases, the entire nail matrix can be involved, leading to the total destruction and permanent loss of the nail plate, known as anonychia.
The second form is Pterygium Ventrale, also known as Pterygium Inversum Unguis, which involves the distal nail unit. Pterygium Ventrale is characterized by the adherence of the hyponychium to the underside of the nail plate. This results in the obliteration of the distal groove, anchoring the nail plate further forward than normal.
While Pterygium Dorsale involves a scarring process that splits the nail, Pterygium Ventrale involves an expansion of the distal nail bed tissue. Both conditions cause dystrophy, but the dorsal type results from a severe, permanent scarring and fibrotic process originating at the proximal nail fold.
Underlying Causes and Associated Disorders
The development of Pterygium Unguis is linked to a prior event that causes intense inflammation and subsequent scarring of the nail matrix. The underlying cause is generally categorized as either acquired or congenital. The most frequent acquired cause is an aggressive inflammatory skin disorder, which triggers a fibrotic process that fuses the nail fold to the nail bed.
Lichen Planus is the inflammatory disease most commonly associated with this condition. The characteristic lymphocytic inflammation damages the nail matrix, initiating the scarring that forms the pterygium. Other autoimmune and connective tissue diseases, such as Systemic Lupus Erythematosus (SLE), cicatricial pemphigoid, and graft-versus-host disease (GVHD), can also lead to this irreversible nail change.
Physical injury to the nail matrix is another significant acquired factor, often resulting in a post-traumatic nail pterygium. Severe trauma, burns, or chronic exposure to radiation (radiodermatitis) can trigger the inflammatory cascade necessary for the skin bridge to form. The resulting inflammation and subsequent healing with fibrosis, rather than the severity of the trauma, is the determining factor.
Less commonly, Pterygium Unguis may be present from birth, suggesting a congenital or genetic component. It is sometimes seen in association with rare genetic conditions like dyskeratosis congenita or multiple pterygium syndrome. In some instances, the condition may be classified as idiopathic, meaning no clear cause is identified, though experts consider these cases a variant of inflammatory disorders like Lichen Planus.
The unifying mechanism is irreversible damage to the keratin-producing cells of the nail matrix. Once damaged by chronic inflammation or trauma, the area heals with dense, fibrous scar tissue that pulls the surrounding skin forward and fuses it to the nail bed. This fibrotic band prevents the normal longitudinal growth of the nail plate, causing the characteristic split and dystrophy.
Clinical Diagnosis and Differentiation
Diagnosis typically begins with a thorough clinical examination by a dermatologist or specialized podiatrist. The physician inspects the affected nail to confirm the characteristic V-shaped scarring and the fusion of the proximal nail fold to the nail bed. Identifying the underlying cause is key, as this dictates the management strategy.
To aid in the diagnosis, dermatoscopy may be used to examine the nail unit under magnification. This non-invasive technique allows for a clearer visualization of the microstructural changes in the nail bed and surrounding skin, helping to assess the extent of the scarring process. If the underlying cause is unclear, or if there is a suspicion of malignancy, a nail biopsy may be necessary.
A biopsy involves taking a small tissue sample for laboratory analysis to definitively confirm the presence of an inflammatory condition like Lichen Planus or Systemic Lupus Erythematosus. This step is important for guiding treatment, as managing the inflammatory disorder can prevent the progression of the pterygium on other nails. The clinical presentation of Pterygium Unguis must be carefully differentiated from other nail conditions.
Crucially, the diagnosis must distinguish Pterygium Dorsale (true Pterygium Unguis) from Pterygium Inversum Unguis (Pterygium Ventrale). The dorsal form is characterized by scarring and proximal fusion that results in a split nail, whereas the ventral form is an overgrowth and adherence of the hyponychium at the distal end of the nail bed. Understanding this distinction is vital for accurate diagnosis and selecting the most appropriate medical intervention.
Treatment and Long-Term Management
Management of Pterygium Unguis focuses on controlling the underlying disease process to prevent further scarring. Since the condition often represents an end stage of damage, the goal is to halt the progression on the affected nail and protect all other nails from developing the same issue. Treating the underlying inflammatory cause is the most effective approach to long-term management.
If an active inflammatory condition like Lichen Planus is confirmed, physicians prescribe potent anti-inflammatory medications. These include topical or intralesional corticosteroids, injected directly into the proximal nail fold. Systemic corticosteroids may be used in early stages to quickly suppress inflammation before irreversible scarring occurs.
Other immunosuppressive agents may be employed for severe or widespread inflammatory disorders to temper the immune response responsible for the damage. By reducing chronic inflammation and fibrotic activity, these treatments aim to stabilize the nail unit and limit the extent of the fusion. This approach is paramount because physical removal of the pterygium without addressing the underlying cause often leads to recurrence.
Surgical intervention, such as nail matrix surgery, can be attempted to physically separate the fused skin from the nail bed. This procedure aims to restore the normal anatomy of the nail unit and allow the nail plate to grow out fully. However, success is highly dependent on whether the underlying inflammatory process is completely inactive.
The risk of the pterygium reforming is high if inflammation persists, as the surgical trauma itself can re-initiate the scarring process. For mild cases or as a maintenance strategy, careful moisturizing of the nail folds and avoiding further trauma are recommended. Long-term management involves continuous monitoring to ensure the underlying disease remains controlled and to watch for any signs of recurrence.