Parakeratosis

Parakeratosis

Parakeratosis refers to retained keratinocytic nuclei in the stratum corneum. It is seen in proliferating keratinocytic disorders such as psoriasis, and in keratinocytic malignancies and premalignant conditions such as Bowen's disease and Solar keratosis. The nuclei are flattened and run  parallel to the epidermal surface.
When you see it look carefully at the underlying epidermis. You may see hyperkeratosis, hypogranulosis and acanthosis.  Histological parakeratosis usually equates to surface scale so think of the mnemonic for the red scaly diseases PMs PETAL for likely diseases.

Patterns of parakeratosis can be helpful.
Confluent in Bowen's disease and Psoriasis         Virtual Slide

Alternating in Solar keratosis                              Virtual Slide

Parakeratosis in a heaped up column in the cornoid lamellae of DSAP   Virtual Slide

Checkerboard parakeratosis in PRP   Virtual Slide

Sandwich parakeratosis over orthokeratosis in Tinea        Virtual Slide

There is also the unusual axillary granular parakeratosis with granules in the stratum corneum. See Virtual Slide

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