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Nailing the Diagnosis of Onychomycosis

The best way to corroborate the clinical diagnosis of onychomycosis remains unclear. It is especially important before beginning expensive oral therapy with terbinafine or an azole to confirm that the nail changes actually result from fungal infection rather than from another cause. Researchers conducted this study to compare the sensitivity of several diagnostic tests for onychomycosis.

The investigators tested nail clippings from 63 patients, most of whom had thickened and discolored toenails, by 6 methods: culture on Mycosel agar; culture on Littman-oxgall agar; routine histopathologic examination with periodic acid-Schiff stain (PAS); potassium hydroxide (KOH) dissolution and centrifugation of the nail followed by the use of PAS; the same procedure followed by fluorescent stain; or followed by chlorazol black E stain. The criterion standard was a positive result with any of these methods. In 25 percent of patients, all tests were negative. The histopathologic examination with PAS had the highest sensitivity (85 percent), and this sensitivity increased slightly but not significantly when combined with the Mycosel agar alone (91 percent) or with both culture techniques (94 percent).

Comment: As the accompanying editorial delineates, the use of nail samples may produce inferior results compared with culturing and examining subungual debris -- especially proximally, where the organisms are usually more plentiful. For most clinicians a KOH preparation of subungual debris should be the initial investigation. If negative, the next step is to culture this material on fungal media. An alternative or additional test, however, is PAS histopathologic examination of nail clippings, whose value this study demonstrates.

— JV Hirschmann

Published in Journal Watch Dermatology October 10, 2000

Citation(s):

Lawry MA et al. Methods for diagnosing onychomycosis: A comparative study and review of the literature. Arch Dermatol 2000 Sep 136 1112-1116.

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• Medline abstract (Free)

Daniel CR III and Elewski BE. The diagnosis of nail fungus infection revisited. Arch Dermatol 2000 Sep 136 1162-1164.

• Original article (Subscription may be required)
• Medline abstract (Free)