Pterygium of nail is seen in -

Ans. is 'a' i.e., Lichen planus Dorsal pterygiumo Winged appearance of nail due to a central fibrotic band divides a nail proximally in two.o Fibrotic band obstructs normal nail growth, eg lichen planusVentral pterygium or pterygium inversum unguiso Occurs on the distal undersurface of the nail, with forward extension of the nail bed epithelium dislocating the hyponychium and obscuring the distal groove.eg:- trauma, systemic sclerosis, Raynaud's phenomenon, lupus erythematosus, familial and infective.