Price V.H., Dept. of Dermatology, University of California, San Francisco; Sawaya M.E., ARATEC Clinics & University of Miami, Miami, Florida; Headington J.T., Dept. of Dermatology & Pathology, Ann Arbor, MI; Kibarian M.K., Dept. of Dermatology, George Washington University, Washington, D.C.

Senescent thinning of the scalp hair, or thinning that occurs after age 60, is poorly understood, and it is unclear whether this is a distinct entity or part of the continuum of androgenetic alopecia (AGA). In a previous study, young males age 18 to 30 with AGA had higher levels of 5.-reductase type 1 and 2, more androgen receptors, and lower levels of cytochrome P-450 aromatase in hair follicles in the frontal region of the scalp than in the occipital region. This study in males age 60 years and older was designed to determine whether the histology and hormonal findings in older males with hair thinning are similar to AGA in young males. Males who experienced the first onset of scalp hair thinning after age 60 were compared to age-matched males (controls) without a history of hair thinning. Four scalp biopsies, two from the frontal and two from the occipital scalp, were obtained for horizontal sectioning and biochemical assay. Histologic findings were primarily follicular downsizing. Follicular drop out was not detected using elastic tissue staining, and there was no significant difference in number of follicles in frontal compared to occipital scalp. Senescent thinning was indistinguishable from androgenetic alopecia in older males. Inflammatory changes were not a significant feature. Biochemical analysis for androgen receptors, 5.-reductase type 1 and 2, and aromatase, in scalp biopsies from older males showed nearly a two fold decrease in levels compared to levels in young males with AGA. In males over 60, androgen receptor and aromatase levels were low and comparable in scalp with and without thinning in both frontal and occipital regions. The 5.-reductase type 1 and 2 levels were only slightly higher in males with thinning hair in both frontal and occipital regions, but the differences were not significant. Histologic and hormonal findings suggest that senescent thinning is a diffuse process that is histologically similar to AGA, but hormonally different and may not be entirely androgen dependent. We hypothesize that senescent alopecia is distinct from AGA.