Comparison of diagnostic methods in the diagnosis of dermatomycoses and onychomycoses

Direct microscopic examination of potassium hydroxide (KOH)-prepared specimens is the simplest, cheapest method used for the diagnosis of mycotic infections of the skin. However, KOH preparations have been reported to have 5-15% of false-negative results, possibly because of the low visibility of scant, scattered fungal material of the nail scrapings and because the detection of fungal elements depends on the skill of the observer [Arch Dermatol133 (1997) 1317; Clin Microbiol Rev8 (1995) 240]. We compared two different KOH-based staining methods in order to obtain reliable results in shorter time than expected for cultures. A total of 124 patients with suspect diagnosis of dermatomycosis or onychomycosis were enrolled. Two scrapings from the same lesion of each patient were stained with KOH-Chlorazole and KOH-Acridine Orange (AO), respectively; cultural examination of the same specimen was considered as diagnostic gold standard. The two methods showed neither significantly different sensitivity nor specificity; however, for onychomycoses, we observed a slightly higher sensitivity for KOH-Chlorazole and a higher specificity for KOH-AO. We suggest the use of both techniques in order to improve detection of fungal infection, especially for onychomycoses.