Epidermal innervation correlates with severity of photodamage. A quantitative ultrastructural study.

Intraepidermal nerve fibers were studied by electron microscopy in chronically photodamaged preauricular skin and in paired sun-protected postauricular sites of 20 Caucasian women aged 56-70 years. As previously reported, basal keratinocytes in the sun-exposed skin showed various degrees of degenerative changes including intracellular vacuolar structures and widened intercellular spaces. Neurites were frequently closely apposed to basal keratinocytes in preauricular sun-exposed skin, but were observed less than 10% as often in sun-protected postauricular skin. When degree of epidermal photodamage was quantified by means of the number of degenerated keratinocytes per 100 keratinocytes in the basal layer, the number of intraepidermal nerve fibers was significantly correlated by linear regression analysis to the severity of epidermal photodamage (r = 0.913) independent of anatomical sites. These results demonstrate for the first time a correlation between degree of epidermal innervation and chronic photodamage and suggest the possibility of neural involvement in the pathophysiology and/or repair of photodamaged skin.