Hyperkeratosis

Excerpt

Hyperkeratosis refers to the increased thickness of the stratum corneum, the outer layer of the skin. Stratum corneum is composed of multiple layers of keratinocyte bodies that, during maturation, produced keratin and subsequently have lost their nucleus and cytoplasmic organelles. The result is a basketweave appearance of anucleate keratinocytes that protect the underlying cells during maturation.

Hyperkeratosis is subclassified as orthokeratotic or parakeratotic. Orthokeratotic hyperkeratosis refers to the thickening of the keratin layer with preserved keratinocyte maturation, while parakeratotic hyperkeratosis shows retained nuclei as a sign of delayed maturation of keratinocytes. Hyperkeratosis can be associated with dyskeratosis. It represents a premature (keratinocytes that are located below the granular cell layer) or abnormal keratinization of individual keratinocytes.

Hyperkeratosis, associated with other abnormalities in the skin biopsy, can be a key to the final histological diagnosis. Epidermal hypertrophy is a benign alteration of the skin that presents with acanthosis (increased thickness of the keratinocyte layers) and hyperkeratosis.