What is the most sensitive test to use when trying to diagnose toenail fungus? — Keri Lazure, PA-C, Omaha, Neb.

Conventional methods for identifying fungal organisms in the nail plate of patients with onychomycosis (OM) include direct microscopy (after KOH solution incubation), fungal culture, and histopathology (using periodic acid Schiff [PAS] stain).

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Surgical pathology testing (of the subungual nail bed and/or the nail plate) using PAS stain is the current gold standard (approaching 100% sensitivity) for the diagnosis of OM.

Newer methods for diagnosing OM include polymerase chain reaction (which has a very high specificity), optical coherence tomography, confocal laser scan microscopy, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and phase contrast hard x-ray microscopy. Confirmation of observations and availability and cost must be considered before these newer methods for diagnosing OM can be incorporated in clinical practice (Indian J Dermatol Venereol Leprol. 2012;78:263-270).— Philip R. Cohen, MD (171-4)

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