Follicular density and ratios in scarring and nonscarring alopecia.

Follicular counts from transverse sectioning of scalp biopsies have not been statistically scrutinized across disease entities in a standardized fashion. We applied uniform histological criteria and strict statistical measures to compare nonscarring and scarring alopecia. We studied 700 consecutive cases including 355 nonscarring alopecia [136 telogen effluvium, 115 alopecia areata (AA), 95 androgenetic alopecia, and 9 trichotillosis] and 345 scarring alopecia [238 central centrifugal cicatricial alopecia, 29 traction alopecia, 26 lichen planopilaris, 21 end-stage alopecia, 20 lupus erythematosus, 11 folliculitis decalvans]. We counted follicular units, anagen, catagen/telogen, and vellus-like follicles at the central follicular unit level. We calculated follicular density per square centimeter, anagen percentage, telogen percentage, anagen to telogen ratio, and terminal to vellus ratio (TVR). The following achieved statistical significance (P < 0.05): follicular density was 249.4 ± 4.6 in nonscarring alopecia versus 120.1 ± 3.8 in scarring alopecia, follicular density of telogen effluvium was 273.5 ± 7.0 (36.5 ± 12.5 above nonscarring alopecia mean), TVR of androgenetic alopecia was 1.6 ± 0.1 (3.6 ± 0.5 below nonscarring alopecia mean), TVR of AA was 3.2 ± 0.4 (1.5 ± 0.6 below nonscarring alopecia mean), anagen percentage of AA was 26.8 ± 1.8 (26.3 ± 3.0 below nonscarring alopecia mean), anagen to telogen ratio of AA was 1.6 ± 0.4 (3.9 ± 0.7 below nonscarring alopecia mean), and telogen percentage of AA was 59.0 ± 2.3 (31.0 ± 3.5 above nonscarring alopecia mean). There exists a great overlap of densities and ratios across the various disorders due to the limited nature of the punch biopsy sample, variations in scalp anatomy, disease biology and duration, patient gender, and age, etc. Our data provide a bell curve distribution that helps analyze hair counts in the clinicopathologic context.