[The ultrastructure of psoriatic nail changes]

The various and subsequent psoriatic nail changes can only be understood on the basis of parakeratotic changes. If parakeratosis is localized in the nail matrix specific changes in the nail will result depending on localization and spreading in the matrix. Punctate indentations (pits) may develop; if there is a ribbon-like, square-dimensioned localization we see streaks and ridges (psoriasis unguis striata). If parakeratotic cells invade the whole of the matrix the so-called psoriasis unguis crateriformis will develop. Well-known to the dermatologist is the irregular salmon-colored patch--a type of psoriasis involving the nail-bed. This salmon-colored patch may finally cause onycholysis semilunaris as the nail plate is not fixed to the nail-bed any longer. There may be onycholysis, too, if the cuticle is involved in the course of the psoriatic change. A long-standing psoriasis of the nails is characterized by para- or hyperkeratotic masses ("Krümelnagel").