Review and Comparison of Histologic Patterns in Alopecia Areata and Androgenetic Alopecia

Summary: Objectives: This study aims to characterize histologic and inflammatory patterns in alopecia areata (AA) and androgenetic alopecia (AGA) to improve diagnostic accuracy in cases with overlapping features. Methods: A board-certified dermatologist reviewed 17 AGA and 49 AA tissue slide specimens using light microscopy from our de-identified teaching slide set. Results: There were no significant differences among cellular infiltrates for peribulbar areas (lymphocytes 82.4% AGA, 79.6% AA, p = 0.597; mast cells 35.3% AGA, 30.6% AA, p=0.639; eosinophils 5.8% AGA, 22.4% AA, p=0.0635), sebaceous glands (lymphocytes 94.1% AGA, 93.9% AA, p=0.514; mast cells 29.4% AGA, 24.5% AA, p=0.655; eosinophils 0% AGA, 8% AA, p=0.112), arrector pili (lymphocytes 70.6% AGA, 77.6% AA, p=0.282; mast cells 23.5% AGA, 22.4% AA, p=0.536; eosinophils 5.9% AGA, 4.1% AA, p=0.621), and fibrous tracts (lymphocytes 64.7% AGA, 81.6% AA, p=0.076; mast cells 35.3% AGA, 28.6% AA, p=0.698; eosinophils 11.8% AGA, 12.2% AA, p=0.479). Higher rates of fibrous tract hyalinization (35.3% AGA, 67.3% AA, p=0.01), fibrous tract melanin pigment casts (5.88% AGA, 46.9% AA, p=0.001), and vellus hair apoptotic bodies (17.6% AGA, 63.3% AA, p= 0.0006) were observed in AA. Conclusion: Preliminary data suggest overlapping patterns of inflammation with distinct differences observed within fibrous tracts and vellus hairs.