Interdigitation index - a parameter for differentiating between young and older skin specimens

Background/aims: Quantitative morphometry developed rapidly during the last decade due to advances is computers and software. We wish to establish a s imple baseline for the morphometric differences due to intrinsic ageing bet ween young and old cohorts: the interdigitation index. It is an expression of the shape of the border between the epidermis and dermis. Methods: We used volar forearm biopsies of women, since the volar forearm i s usually not photodamaged. The biopsies were fixed in buffered formalin, e mbedded in paraffin and sectioned. Separate sections were stained by hemato xylin-eosin, by orcein and by dimethyl-methylene blue. We had seven female volunteers in each group; the young cohort had a mean age of 26.6 years, th e older cohort 50.9 years. We chose a cohort that was just about postmenopa usal, since in the future we wish to evaluate the effect of externally-appl ied agents on postmenopausal female skin and the earlier it is applied the better its chance of being effective. Results: We found no difference between the young and older cohort with reg ard to epidermal thickness. We found a decrease of glycosaminoglycen (GAG) as measured by dimethyl-methylene blue staining. The results of the elastic staining by orcein, although in line with the reports in the literature, a re not useful for evaluating the intrinsic ageing process, at least not by the simple percentage of area stained procedure. We introduced a new parame ter: the interdigitation index. It is a simple measurement of the interdigi tation in the epidermal-dermal junction, known to be diminished by age. Thi s index was diminished by about 20% between the young and older cohort. Conclusions: Quantitative morphometry using simple epidermal and dermal mea surements on biopsies of the volar forearm of women is suitable for followi ng intrinsic ageing of the skin and offers a simple objective method for fo llowing the ageing process of the skin.