Histopathologic Patterns in Dermatophyte Infections

Abstract

Background: Dermatophyte infections (DI) mimic a wide range of inflammatory diseases clinically and hyphae often play hide and seek on microscopy. Pathologists encounter biopsies with no clinical suspicion. In such instances, we need to recognize clues that point to the diagnosis. Aim: This study aims to describe the histopathologic patterns in DI. Materials and Methods: A total of 20 cases of DI were reviewed for various epidermal and dermal patterns. Results: Altered pattern of cornification was seen in all 20 cases (100%), the commonest being parakeratosis (75%), often in small mounds (55%), followed by compact orthokeratosis (50%). Neutrophils (65%) and crusting (55%) were seen, with sandwich sign noted in 65% cases. The reaction pattern most commonly seen was spongiosis (50%). Pustules were rare (20%). Mild superficial perivascular lymphocytic infiltrate (45%) was the commonest dermal pattern. Neutrophils (45%) and eosinophils (25%) were less frequent. Fungal hyphae were identified either within the zone of compact orthokeratosis (55%) or at the junction between two different patterns of cornification (45%). The limitations of this study are relatively small number of cases studied and lack of correlation with fungal culture, as they were not done in 90% of patients due to lack of clinical suspicion. Conclusion: Histopathologic patterns in DI are most often subtle, in the form of small mounds of parakeratosis and mild superficial perivascular dermal infiltrate, which overlap with several other skin diseases. Neutrophils and sandwich sign are not seen in almost half the cases. A careful search for fungi together with periodic acid–Schiff stain is mandatory whenever altered cornification is seen. Investigations such as potassium hydroxide preparation and cultures are not done unless there is clinical suspicion, which is absent in majority of the cases. Histopathology offers the only opportunity to establish a diagnosis in this easily curable condition.