orthokeratosis

Orthokeratosis is a term used in skin histopathology to describe a pattern of keratinization in which the stratum corneum is thickened and composed of anucleate, fully cornified cells (corneocytes). In orthokeratosis, the granular layer is usually present and well developed, reflecting a normal maturation process of keratinocytes. This contrasts with parakeratosis, where nuclei persist in the cells of the stratum corneum.

As a descriptive histologic pattern, orthokeratosis can be seen in a variety of circumstances. It may occur in normal or thickened epidermis of weight-bearing skin, such as the palms and soles, where hyperkeratosis is orthokeratotic. It can also be observed in healing or regressive dermal processes, where the epidermis regenerates with an intact granular layer and anucleate corneocytes. In many conditions, orthokeratosis is present alongside other features such as acanthosis or dermal inflammation, and it may be accompanied by hyperkeratosis without parakeratosis.

Clinical relevance of orthokeratosis lies in its being a non-specific histologic pattern. Its presence must be interpreted in the context of other microscopic findings and the clinical picture, since several dermatoses may show orthokeratotic keratinization either alone or in combination with other changes.