The Role of Histological Examination of Nail Clipping in the Diagnosis of Onychomycosis.

BACKGROUND: Diagnosis of onychomycosis is based on potassium hydroxide (KOH), direct smear, culture, and polymerase chain reaction. Nail clippings are rarely used as a diagnostic tool.

OBJECTIVES: To evaluate nail clippings for the diagnosis of onychomycosis and to compare it to KOH smears.

METHODS: Nail clipping specimens of 39 patients were collected: 34 with onychomycosis proved by positive culture and 5 from normal nails. The specimens were submitted to histological processing and then stained with periodic acid-Schiff (PAS) and Grocott-Gomori's methenamine silver (GMS) stains. For each nail, KOH smear was also performed. Two pathologists who had no information on the KOH smear and the culture results evaluated the nail clipping histology for the presence of fungal element. Their assessment was compared to the KOH smear and culture results.

RESULTS: Of the 34 specimens that had positive culture, 25 were dermatophytes, 5 were molds, and 4 were candida. Clipping specimens were positive in 30 cases (88%): 23/25 dermatophyte, 4/5 molds, and 3/4 candida. Pathologists were able to classify the pathogens into dermatophytes and non-dermatophytes based on the morphology. PAS stain results were the same as GMS in evaluation of the nail specimen. KOH smear was positive in 29 nails (85%): 20/25 dermatophytes, all 5 molds, and 4 candida. In all five nails where the culture was negative, both clipping and KOH smear did not show fungal elements.

CONCLUSIONS: Nail clippings can serve as a rapid, inexpensive, and reliable method for evaluation of onychomycosis, comparable to KOH smear, with the advantage of pathogen group identification.