Polarized Versus Diffractive Microscopy in Distinguishing Scarring From Non‐Scarring Alopecia

ABSTRACT Background The histologic diagnosis of alopecia can be challenging. Polarized light microscopy and diffractive microscopy can be performed without added cost or the need for special stains. We sought to determine if they can be of value in the diagnosis of alopecia biopsy specimens. Methods We retrospectively reviewed 152 deidentified alopecia scalp biopsy slides (80 non‐scarring and 72 scarring) with polarized and diffractive microscopy and analyzed the performance of each method. Results Fibrous tracts were evaluable in 150 of the 152 specimens. One was excluded as the dermis was completely replaced by scar and one demonstrated follicles but no empty fibrous tracts. Intensity of polarization and diffraction differed between scarring and non‐scarring alopecia, with clearer separation in polarized microscopy ( p  < 0.001) compared with diffractive microscopy ( p  = 0.029). Polarized intensity showed good discrimination ( AUC 0.804) with high specificity (94.9%) and modest sensitivity (49.3%). In contrast, grading diffractive intensity added little to a simpler bimodal scale ( AUC 0.585). A circumferential perifollicular halo was more common in non‐scarring alopecia, especially androgenetic alopecia. Conclusion Polarized light microscopy outperformed diffractive microscopy for distinguishing scarring from non‐scarring alopecia and provides a highly specific adjunct to simple microscopy.