Subtle intracorneal findings in inflammatory disorders: hyphae or not?

Background: Spongiotic and lichenoid dermatitides are frequently stained with periodic acid‐Schiff (PAS) stains to check for the presence of dermatophytes. PAS+ structures without a septate morphology are often seen with lichenoid dermatitides, however, their nature has not been previously characterized. Methods: Fifteen consecutive biopsies of lichenoid and five spongiotic dermatitides were stained with hematoxylin and eosin (H&E), PAS, and antibodies to CD1a. Results: Twelve of 15 lichenoid and none of the five spongiotic dermatitis showed PAS+ structures in the stratum corneum. Distinct septation or branching was not identified in these PAS+ structures. Eleven of 15 from the lichenoid group, but none from the spongiotic group, showed CD1a+ structures in the stratum corneum. This staining pattern suggests that the intracorneal structures represent the dendritic processes of Langerhans' cells (LCs) within the stratum corneum. Conclusions: PAS+ and CD1a+ structures are present in the stratum corneum of lichenoid, but not in spongiotic, dermatitis. This study morphologically confirms extension of LC dendrites into the stratum corneum in lichenoid but not in spongiotic dermatitides.