What is the best method of diagnosing onychomycosis?

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What is the best method of diagnosing onychomycosis?

J Fam Pract. 2003 December;52(12):919-941

By

Cathy Rea, MD

Mark H. Greenawald, MD

BACKGROUND: Treatment of onychomycosis requires long-term and expensive therapy with potential negative side effects. Diagnosis based on clinical findings tends to overestimate fungal disease, as only 50% of dystrophic nails have a fungal cause. Traditional diagnostic methods have shown inconsistent sensitivity.
POPULATION STUDIED: The study evaluated 105 patients with suspected onychomycosis presenting to an outpatient dermatology clinic. No information was provided on patient demographics or exclusion criteria. Seventy-two percent of patients had onychomycosis.
STUDY DESIGN AND VALIDITY: The investigators evaluated 105 patients with suspected onychomycosis via 4 diagnostic methods. For periodic acid–Schiff staining, nails were clipped with standard nail clippers at the distal free edge of the nail plate, including any attached subungual debris, and placed in a 10% formalin solution for evaluation by a pathologist. Subungual curettage was then used to obtain material that was evenly divided for KOH preparation, fungal culture, and calcofluor white staining.
OUTCOMES MEASURED: The authors calculated the sensitivity, specificity, PV+, and PV– of KOH preparation, fungal culture, and periodic acid–Schiff staining using calcofluor white as the reference standard.
RESULTS: Overall, 93/105 patients tested positive with at least 1 of the diagnostic methods. A total of 76 (72%) samples were positive by calcofluor white, the reference standard. The sensitivities of the other techniques were as follows: periodic acid–Schiff staining, 92%; KOH preparation, 80%; fungal culture, 59%. Periodic acid–Schiff staining was significantly more sensitive than KOH preparation (P=.03) and both periodic acid–Schiff staining and KOH preparation were significantly more sensitive than culture (P=.00002). The specificity of fungal culture was 82% vs 72% for both periodic acid–Schiff staining and KOH preparation. This difference was not statistically significant.

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What is the best method of diagnosing onychomycosis?

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