Examination Of Nail Clippings For Onychomycosis: Histologic Observations With Microbiologic Correlations

Abstract

Abstract Introduction/Objective Appropriate management of onychomycosis, the most common disease of the nail unit, depends on accurate and timely diagnosis. Histologic evaluation of nail clippings, paired with histochemical techniques such as Periodic acid-Schiff (PAS), is a rapid, sensitive method for diagnosis of onychomycosis. While studies have compared testing modalities for onychomycosis, few have systematically evaluated histologic changes of the nail plate and correlated findings with concomitant microbiologic culture. Methods A consecutive series of nail clipping specimens between July 2016 to July 2019 from our institution were evaluated. Clinical data were collected, H&E and PAS stains were examined for histologic nail plate alterations and fungal presence, morphology, location, and abundance. Concurrent culture results were also collected and correlated. Results Histologic slides, including PAS, of nail clippings were evaluated from 131 patients (median age 57, 65% female). 53 cases (40%) were positive for fungal organisms by PAS stain: 26 cases showed diffuse fungal involvement, while 27 cases showed focal fungal involvement, limited to one 200x field. Of the PAS-positive cases, 47 cases showed predominantly hyphae and 6 cases showing predominantly yeast-like morphology. Nail plate histologic changes associated with PAS positivity included parakeratosis (p= 0.0071) and neutrophilic aggregates (p=0.0017). Of the total cases evaluated by histology, 67 cases had concomitant cultures performed, with 17 of these cases (25%) positive for fungal growth. Of the 23 PAS-positive cases with simultaneous culture sent, only 9 cases (39%) were positive for fungal growth. Conversely, of the 44 PAS-negative cases with simultaneous culture sent, 8 cases (18%) were positive for fungal growth. For cases positive by both PAS and fungal culture, significant correlations between fungal morphology on PAS and microbiologic speciation were not observed. Conclusion While PAS stains appear overall more sensitive for onychomycosis, both PAS and culture methods are falsely negative in a significant number of cases. In cases of high clinical suspicion for onychomycosis, consideration of employing more than one testing modality is recommended. Of note, histologic examination may reveal nail plate changes associated with fungal infestation, including nail plate parakeratosis and neutrophilic aggregates.