Hematoxylin–Eosin Histology for Detection of Dermatophytosis: A Retrospective Cohort Selection Diagnostic Accuracy Study

Background

Dermatophytes can be identified in hematoxylin–eosin (H&E) histologic preparations, but the diagnostic accuracy of this approach and the relative need for ancillary periodic acid–Schiff (PAS) testing are unknown.

Methods

A cohort selection cross-sectional study with repeated measures was utilized to measure the accuracy of four blinded assessors at different levels of experience and training in detecting fungal hyphae in H&E slides from 100 consecutive cases selected based on prior PAS testing to exclude dermatophytosis.

Results

Dermatopathology training was associated with an accuracy of 0.97 (95% CI: 0.93, 1.00), a sensitivity of 0.78 (95% CI: 0.50, 1.00), and a specificity of 0.99 (95% CI: 0.96, 1.00). Accuracy for non-dermatopathologist assessors improved after completing an educational module (from 0.64 to 0.84) but was limited by low sensitivity. False positive classifications by the dermatopathology assessor were only seen in nail clipping specimens. False negative classifications were seen in cases with low fungal burdens, topical corticosteroid treatments, and comorbid conditions.

Conclusions

Experienced dermatopathologists can usually identify dermatophytosis with H&E staining. These findings indicate that PAS testing should be selectively applied to cases with suspected dermatophytosis where no organisms are visible on H&E, on nail clips where H&E may be unreliable, and in evaluations by non-dermatopathologists.