What it means

PEH is a reaction pattern, not a single disease.
It consists of irregular downward squamous epithelial hyperplasia that can look invasive at low power.
Unlike invasive SCC, maturation is usually retained and cytological atypia is limited or reactive, but this distinction may be difficult in small biopsies.
The pathologist may use the term when the appearances favour a reactive process but clinicopathological correlation is essential.
PEH can coexist with, overlie or obscure a clinically important underlying process.

Associations

Chronic ulcers, sinus tracts, burns, scars and longstanding inflammatory dermatoses.
Infections, including deep fungal infection, atypical mycobacteria, tuberculosis, leishmaniasis and chronic bacterial infection.
Granular cell tumour, where overlying PEH can be prominent and lead to an erroneous SCC diagnosis if the dermal tumour is missed.
Prurigo nodularis, hypertrophic lichen planus, chronic trauma and foreign-body reactions.
Keratoacanthoma-like and verrucous lesions, where adequate sampling of the base and architecture is crucial.

Provide the clinical differential and lesion duration; “rule out SCC” is useful information for the dermatopathologist.
A superficial shave may show only reactive squamous hyperplasia and miss invasive SCC, infection or an underlying tumour.
If SCC is a real concern, sample the thickest/most indurated area and include adequate dermis; consider incisional, punch or excisional biopsy depending on site and size.
Histology should be interpreted with the clinical picture: preserved maturation and limited atypia support PEH, but destructive invasion, marked atypia or perineural/lymphovascular invasion support SCC.
Ancillary stains or molecular tests may help in selected difficult cases, but they do not replace adequate tissue and clinicopathological review.

Treat the underlying trigger when PEH is confidently reactive: infection, chronic ulceration, inflammatory dermatosis or trauma.
If the lesion is clinically suspicious, enlarging, ulcerated, painful, indurated, recurrent or high-risk by site/patient, re-biopsy deeper or excise despite an initial PEH report.
If PEH overlies a tumour such as granular cell tumour, management follows the underlying diagnosis rather than the epithelial reaction.
Discuss discordant cases directly with dermatopathology and provide clinical photographs where available.
Document the safety-net plan because PEH is a common source of benign-versus-SCC diagnostic ambiguity.

Assuming PEH is always harmless can delay diagnosis of well-differentiated SCC.
Assuming PEH is SCC can lead to over-treatment of infection or inflammatory disease.
A biopsy from ulcer slough or the edge of a chronic wound may not answer the cancer question.
Granular cell tumour can be missed if the biopsy samples only the epithelial hyperplasia.
Repeated “reactive” reports should be challenged if the lesion is clinically getting worse.