Table 1.

Classification of actinic keratosis based on histologic features

Variant	Characteristics
Hypertrophic	Pronounced hyperkeratosis with areas of parakeratosis
	Thickened epidermis
	Irregular downward proliferation
	Keratinocytes in stratum malpighii (may show loss of polarity and pleomorphism)
Atrophic	Generally atrophic epidermis with slight hyperkeratosis
	Basal layer shows cells with hyperchromatic nuclei
	Cells may proliferate towards dermis as buds or duct-like structures
Bowenoid	Difficult to distinguish from Bowen disease
	Full thickness atypia present
Acantholytic	Intercellular clefts present as result of anaplastic changes in base of epidermis that produce dyskeratotic cells with disrupted cellular bridges
Epidermolytic	Granular degeneration or epidermolytic hyperkeratosis
Lichenoid	Dense dermal infiltrate of lymphocytes in papillary dermis that damages epidermis basal layer
Pigmented	Excessive amounts of melanin in basal epidermis
	Numerous melanophages in superficial dermis

Reproduced with permission from Rosen et al. [7]