Successive Potassium Hydroxide Testing for Improved Diagnosis of Tinea Pedis

The gold standard for diagnosing dermatophytosis is the use of direct microscopic examination together with fungal culture.¹ However, in the last 2 decades, molecular techniques that currently are available worldwide have improved the diagnosis procedure.^2,3 In the practice of dermatology, potassium hydroxide (KOH) testing is a commonly used method for the diagnosis of superficial fungal infections.⁴ The sensitivity and specificity of KOH testing in patients with tinea pedis have been reported as 73.3% and 42.5%, respectively.⁵ Repetition of this test after an initial negative test result is recommended if the clinical picture strongly suggests a fungal infection.^6,7 Alternatively, several repetitions of direct microscopic examinations also have been proposed for detecting other microorganisms. For example, 3 negative sputum smears traditionally are recommended to exclude a diagnosis of pulmonary tuberculosis.⁸ However, after numerous investigations in various regions of the world, the World Health Organization reduced the recommended number of these specimens from 3 to 2 in 2007.⁹

The literature suggests that successive mycological tests, both with direct microscopy and fungal cultures, improve the diagnosis of onychomycosis.^1,10,11 Therefore, if such investigations are increased in number, recommendations for successive mycological tests may be more reliable. In the current study, we aimed to investigate the value of successive KOH testing in the management of patients with clinically suspected tinea pedis.

Methods

Patients and Clinical Evaluation
One hundred thirty-five consecutive patients (63 male; 72 female) with clinical symptoms suggestive of intertriginous, vesiculobullous, and/or moccasin-type tinea pedis were enrolled in this prospective study. The mean age (SD) of patients was 45.9 (14.7) years (range, 11–77 years). Almost exclusively, the clinical symptoms suggestive of tinea pedis were desquamation or maceration in the toe webs, blistering lesions on the soles, and diffuse or patchy scaling or keratosis on the soles. A single dermatologist (B.F.K.) clinically evaluated the patients and found only 1 region showing different patterns suggestive of tinea pedis in 72 patients, 2 regions in 61 patients, and 3 regions in 2 patients. Therefore, 200 lesions from the 135 patients were chosen for the KOH test. The dermatologist recorded her level of suspicion for a fungal infection as low or high for each lesion, depending on the absence or presence of signs (eg, unilateral involvement, a well-defined border). None of the patients had used topical or systemic antifungal therapy for at least 1 month prior to the study.¹²

Clinical Sampling and Direct Microscopic Examination
The dermatologist took 3 samples of skin scrapings from each of the 200 lesions. All 3 samples from a given lesion were obtained from sites with the same clinical symptoms in a single session. Special attention was paid to samples from the active advancing borders of the lesions and the roofs of blisters if they were present.¹³ Upon completion of every 15 samples from every 5 lesions, the dermatologist randomized the order of the samples (https://www.random.org/). She then gave the samples, without the identities of the patients or any clinical information, to an experienced laboratory technician for direct microscopic examination. The technician prepared and examined the samples as described elsewhere^5,7,14 and recorded the results as positive if hyphal elements were present or negative if they were not. The study was reviewed and approved by the Çukurova University Faculty of Medicine Ethics Committee (Adana, Turkey). Informed consent was obtained from each patient or from his/her guardian(s) prior to initiating the study.

Statistical Analysis
Statistical analysis was conducted using the χ² test in the SPSS software version 20.0. McNemar test was used for analysis of the paired data.