Supplementary Material for: Utility of Horizontal Sections of Scalp Biopsies in Differentiating between Androgenetic Alopecia and Alopecia Areata

Background: Androgenetic alopecia (AGA) and alopecia areata (AA) are common causes of alopecia which can sometimes be difficult to differentiate clinically. Horizontal sections of scalp biopsies are used to study non-cicatricial alopecias due to the ability to perform both quantitative and morphometric analysis of hair follicles on them. Methods: It was a prospective, cross-sectional study conducted to assess the utility of horizontal sections to differentiate between the alopecias. Fifty-two cases were included: 20 cases of male AGA, 11 of female AGA and 21 cases of AA. After clinical examination and dermoscopy, a skin biopsy was taken and subjected to transverse sectioning. Histopathological assessment was done by two dermatopathologists blinded to clinical details. Results: Among the quantitative parameters, terminal:vellus hair ratio (3.08 in AGA and 1.83 in AA, p = 0.0091) and anagen:non-anagen hair ratio (9.25 in AGA and 3.56 in AA, p = 0.0021) were significantly lower in AA. In qualitative parameters, peribulbar inflammation was seen in 63% of AA cases (p = 0.0001). Pigment casts were seen in twice the number of AA (57%) than AGA (26%) cases. Broad avascular stelae and focal trichomalacia were seen in 9.5% of AA cases. Conclusion: Besides peribulbar inflammation, we found a lower anagen:non-anagen hair ratio and presence of pigment casts in transverse sections of scalp biopsies favouring AA over AGA.