Understanding nail disorders.

Diagnosing nail dystrophies and understanding their pathogenesis is best accomplished if the origin of the disorder is first established. Exogenous. In this group, the nail plate is altered by exogenous factors and is the site of primary involvement: periungual tissues may be affected secondarily. Endogenous. In this group, the nail plate is altered secondarily by changes occurring in the matrix, proximal nail fold, nail bed, hyponychium or underlying bony phalanx.