ROUTINE HISTOLOGIC EXAMINATION FOR THE DIAGNOSIS OF ONYCHOMYCOSIS - AN EVALUATION OF SENSITIVITY AND SPECIFICITY

Clinical differentiation of dermatophyte infection from dystrophic cha nges due to psoriasis may be challenging, Typically, potassium hydroxi de (KOH) preparations, fungal culture, and occasionally, nail unit bio psy specimens are utilized to help differentiate between the two. Thes e tests are often time-consuming and may yield false-negative results. Increasing regulation of the office laboratory has caused some physic ians to forgo this testing, which was previously routine. We investiga ted the utility of routine histologic examination of nail clippings in differentiating onychomycosis from psoriatic onychodystrophy. Twenty- three distal nail clipping specimens (twelve specimens from patients w ith onychodystrophy of unknown cause and eleven control specimens from nails with known cause) were evaluated by routine histology and perio dic acid-Schiff (PAS) staining. Of the dystrophic cases, four were dem onstrated to be onychomycosis by the presence of hyphae on histologic evaluation and by culture, whereas only three of these cases yielded p ositive results on KOH examination. Eight cases of onychodystrophy wer e due to psoriasis. Yeast forms were detected on one case of psoriatic onychodystrophy that demonstrated yeast growth on culture. In our stu dy, routine histologic examination with PAS staining was equal to cult ure and superior to KOH preparation in leading to the correct diagnosi s of dermatophyte infection. In addition, the diagnosis of psoriasis o f the nail plate was detected accurately by routine histologic examina tion. Routine histologic examination with PAS staining is a rapid, sim ple, and reliable test in the evaluation of onychodystrophy.