Table 1.

Causes of dorsal pterygium involving the nail unit

Traumatic causes	Acute trauma: burns, penetrating injury, radiodermatitis, split nail deformity
	Chronic trauma: onychotillomania
Dermatological diseases	Lichen planus (involving the nail matrix)
	Toxic epidermal necrolysis
	Porokeratosis of Mibelli
Bullous diseases	Autoimmune bullous diseases: cicatricial pemphigoid, pemphigus foliaceus, pemphigus vulgaris, etc.
	Mechanobullous diseases: epidermolysis bullosa (various variants)
	Bullous drug reactions with scarring
Infections	Purulent infections
	Leprosy (neuropathic damage or secondary purulent infections)
Genodermatoses	Dyskeratosis congenita
	Marfan syndrome
Nail tumors	Onychomatricoma (matrix metaplasia of the ventral aspect of PNF)
Systemic disease	Graft versus host disease
	Systemic lupus erythematosus
	Sarcoidosis (involving the PNF)
Vascular causes	Raynaud's phenomenon
	Atherosclerosis
	Diabetic vasculopathy
	Type 2 lepra reaction
Idiopathic pterygium

PNF, proximal nail fold.