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15-04-2010 | Dermatology | Article

PAS staining optimal for diagnosing onchomycosis


Free abstract

MedWire News: Periodic acid schiff (PAS) staining is as effective as Gomori methenamine silver (GMS) staining for diagnosis of onchomycosis, but significantly less expensive, say investigators.

Both PAS and GMS are used to stain histopathological nail plate specimens and diagnose onchomycosis, but there has been some debate about which technique is superior.

Thomas Horn (Caris Research Institute, Newton, Massachusetts, USA) and colleagues tested 1225 consecutive nail specimens with suspected onchomycosis using the PAS (standard) staining technique.

Of these, 580 were PAS negative and 645 were positive for onchomycosis. To test whether GMS is a superior technique, additional nail samples were obtained from 326 of the PAS negative individuals and stained with GMS. As a control, an additional 190 samples taken from previously PAS negative individuals were retested using PAS.

Writing in the Journal of Cutaneous Pathology, the team reports that 4.3% (n=14) of the GMS tested samples were positive for onchomycosis compared with 4.2% (n=8) of the samples re-tested with PAS, a nonsignificant difference.

Horn and co-authors estimated the cost of performing one PAS stain to be US$6.16 (€4.54), whereas performing one GMS stain was estimated to cost US$16.62 (€12.27). In this experiment, each positive GMS or PAS stain obtained by testing samples from previously PAS negative nails cost the laboratory US$387.01 and US$146.30 (€285.74 and €108.02), respectively.

Overall, this amounted to PAS staining being 2.6-fold less expensive than GMS staining.

“Taken together, these data suggest that the PAS stain is the optimal method for diagnosing onychomycosis,” conclude Horn et al.

“Future studies examining the objective benefits of each stain such as speed and ease of diagnosis may be helpful,” say the authors. “In spite of this, we believe that PAS, from the perspective of both diagnosis and cost, is the gold standard for the identification of onychomycosis.”

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

By Helen Albert