Parakeratosis and acanthosis
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
View the Video of this Topic
Acanthosis
This usually results from keratinocyte hyperplasia and features acanthosis of the epidermis. Often there is associated hyperkeratosis.
Check it to see if there is any cytological atypia of the keratinocytes to indicate Bowen's disease.
Otherwise a lot of chronic diseases eg Lichen simplex and Psoriasis will show a thickened epidermis but look out for some Deep fungal infections, TB of the skin and Reactive perforating collagenosis and the much rarer halogenodermas.
