DNA-based-detection-for-onychomycosis_Dermatology-Online-Journal
Onychomycosis is a prevalent disease of the nail. Traditional methods for diagnosis include direct microscopy with potassium hydroxide (KOH microscopy) and fungal culture.

OUR PATHOLOGY SERVICES | PHYSICIAN RESOURCES | INSTRUCTIONAL VIDEOS | ORDER LAB SUPPLIES | FIND AN ACCOUNT MANAGER

Traditional methods for diagnosis include direct
microscopy with potassium hydroxide (KOH
microscopy) and fungal culture. Other techniques
using histochemical staining have higher sensitivity,
but cannot identify genus or species of the infecting
agent. PCR assays are sensitive, specific, and capable
of genus and species level identification. We describe
a real-time PCR assay for 15 different fungi that are
associated with onychomycosis. Of 425 clinical
samples suspected of onychomycosis analyzed by
fungal culture and PCR, 219 samples were positive for
both (52% agreement). Of the 206 discordant
samples, 95% were resolved in favor of PCR by DNA
sequencing. On a larger data set of 2,452 samples,
positivity rates for histopathology, PCR, and culture
were 85%, 73%, and 54% respectively. Further, 48%
of PCR positive and 51% of histopathology positive
samples were negative by culture. PCR outperformed
culture compared to histopathology for sensitivity
(80% versus 49%), specificity (92% versus 79%),
positive predictive value (94% versus 77%), and
negative predictive value (76% versus 52%). These
results indicate the culture method lacks the
sensitivity to be a reliable assay for onychomycosis,
that PCR and histopathology are highly concordant,
and that PCR provides the highest degree of
diagnostic accuracy available.