A cross-sectional observational study showing sebaceous glands differences between psoriatic alopecia and alopecia areata

This study shows that there is a distinct difference in the proportion of mature to immature sebocytes between psoriatic alopecia and AA with almost 3 times more mature sebocytes in AA. It also conﬁrms previous observations about sebaceous gland size in psoriatic alopecia and AA. 5 Sebaceous gland in AA are 50% larger than in psoriatic alopecia. Taken together, gland size and sebocytes maturity provide a reliable histopathologic aid which is useful in distinguishing the dermal changes in AA from psoriatic alopecia. This can help prevent an overdiagnosis of AA in patients with psoriasis only. Further study of the sebaceous gland features of a larger set of cases of AA, including variants of AA, and other AA histologic simulants is warranted

To the Editor: The dermal histopathologic changes in psoriatic alopecia can mimic subacute alopecia areata (AA).These 2 disparate diseases both have follicular miniaturization, a dramatic catagen/ telogen shift, and a superficial lymphocytic infiltrate. 1 Unfortunately, the subacute phase of AA often has a sparse lymphocytic infiltrate and only rarely has the hallmark peribulbar ''swarm-of-bees'' lymphocytic infiltrate.Thus, it is sometimes not possible to determine whether a patient has psoriasis alone or psoriasis with associated AA.An overdiagnosis of AA may make a patient's care confusing.
Previous studies have reported sebaceous gland ''atrophy'' (or complete absence) in psoriatic alopecia 2 and a small volume 3 ; and a normal-todecreased number of sebaceous glands in AA. 4 Despite these observations, no one has compared the 2 diseases side-by-side to determine whether additional histologic features exist which can be useful in distinguishing them from each other.
We compared the size and histologic features of sebaceous glands from biopsies with definitive diagnoses of psoriatic alopecia or AA made by 2 of the authors with expertise in hair loss disorders, 1 a clinician and 1 a dermatopathologist.There were 40 Caucasian from a single clinic in Italy, matched as closely as possible by age and gender (20 psoriatic alopecia [average age 43.8 years; 80% female]; 20 AA [average age 45.3 years; 75% female]).A single 4 mm archival biopsy from the margin of each lesion was analyzed for each patient.The transverse sectioning technique allowed evaluation of all histologic levels of the tissue segment.The percentages of large, pale-staining ''mature'' and small, bluestaining ''immature'' sebocytes were estimated from cross-sectional images.
Surface areas of sebaceous glands were measured from the largest gland identified using closedfreeform annotation tools built into the Philips IntelliSite Digital Pathology Solutions system.
There was a large difference in the proportions of mature and immature sebocytes.In psoriatic alopecia 29.8% of sebocytes were mature, and the remaining were immature (Fig 1).In AA, in contrast, 87.4% of sebocytes were mature and the remaining were immature (Fig 2) (P \.00001).
The mean sebaceous gland area of psoriatic alopecia were 50% smaller than those of AA.Psoriatic alopecia had a mean surface area of 0.12 mm 2 (P ¼ .013),whereas the largest sebaceous gland in AA was 0.18 mm 2 (P ¼ .028and P ¼ .013,respectively; 1-tailed t test).This study shows that there is a distinct difference in the proportion of mature to immature sebocytes between psoriatic alopecia and AA with almost 3 times more mature sebocytes in AA.It also confirms previous observations about sebaceous gland size in psoriatic alopecia and AA. 5 Sebaceous gland in AA are 50% larger than in psoriatic alopecia.Taken together, gland size and sebocytes maturity provide a reliable histopathologic aid which is useful in distinguishing the dermal changes in AA from psoriatic alopecia.This can help prevent an overdiagnosis of AA in patients with psoriasis only.Further study of the sebaceous gland features of a larger set of cases of AA, including variants of AA, and other AA histologic simulants is warranted. 1tty Nguyen, BS, a,b Curtis T.