Methods for diagnosing onychomycosis - A comparative study and review of the literature

Objective: To identify the sensitivity of several readily available diagnostic tests for onychomycosis, Design: Cross-sectional study. Setting: Dermatology and podiatry departments at a teaching hospital. Patients: Sixty-three adult men and women with a clinical examination highly suggestive of onychomycosis. Main Outcome Measures: Sensitivity of each test and of several test combinations. Results: Nail samples underwent 6 diagnostic tests. Routine histopathologic examination with periodic acid-Schiff stain (PAS) (PATHPAS) was 85% sensitive, Sensitivities for potassium hydroxide dissolution and centrifugation combined with PAS, fluorescent brightener, or chlorazol black E were 57%, 53%, and 53%, respectively. Culture on Sabouraud agar with chloramphenicol and cycloheximide (Mycosel agar) was 32% sensitive; on Littman-oxgall agar, 23% sensitive. The most sensitive combination of tests, both culture methods plus PATHPAS, was 94% sensitive (not statistically different from the sensitivity of PATHPAS alone [P=.26]). Conclusions: When onychomycosis is suspected clinically, PATHPAS of the nail is the single most sensitive of the diagnostic tests we evaluated. Because it is quickly performed and relatively operator independent, PATHPAS is practical for clinical and research purposes. Further study is needed to determine if sensitivity may be enhanced by combining PATHPAS with cultures obtained by several collection methods (clipping, curettage, and shaving). Such combinations may serve as sensitive and efficient strategies for diagnosing onychomycosis.