parakeratosis

Parakeratosis is a histopathologic term describing a mode of keratinization in which keratinocytes in the stratum corneum retain their nuclei. In normal epidermis, keratinocytes lose their nuclei as they move into the outermost layer; parakeratosis indicates abnormal keratinocyte maturation or accelerated turnover.

Histologically, parakeratosis is seen as retention of nuclei within the cells of the stratum corneum, often accompanied by hyperkeratosis (thickened stratum corneum) and a diminished or absent granular layer. The pattern can be focal or diffuse and may occur alongside other epidermal changes such as acanthosis or spongiosis, depending on the underlying condition. In psoriasis, parakeratosis is typically present with thinning of the granular layer and may be accompanied by neutrophils in the stratum corneum (Munro microabscesses).

Parakeratosis is not disease-specific but is a feature of several dermatologic conditions. It is classically associated with psoriasis and can be found in actinic keratosis, chronic dermatitis, and other processes with rapid epidermal turnover. It may also be observed in mucosal epithelia, where parakeratotic change can occur in conditions such as leukoplakia or smoker’s keratosis.

Clinical significance centers on its interpretation in biopsy specimens. Parakeratosis helps distinguish patterns of keratinization from orthokeratosis, where the stratum corneum is anucleate without retained nuclei. Its presence supports diagnoses that involve accelerated epidermal maturation and abnormal terminal differentiation, but it is not diagnostic of a single disease.