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Onychomycosis is an under-recognized healthcare burden. Despite the risk of misdiagnosis, confirmatory laboratory testing is under-utilized. Histopathologic examination with polymerase chain reaction (PCR) is currently the most effective diagnostic method; it offers direct detection and identification of a fungal invasion. In this retrospective cohort study, we assessed confirmatory testing results, with matching clinical diagnoses, in 96,293 nail specimens submitted during a 9-month period from 2022 to 2023. Toenail specimens were examined using fungal culture, histopathology and/or PCR. Clinical diagnoses were identified using the International Classification of Diseases 10th Revision codes. For clinically diagnosed onychomycosis patients, the overall positivity rate was 59.4%; a similar positivity rate (59.5%) was found in patients with clinically diagnosed non-fungal nail dystrophy. Performing a histopathologic examination with PCR was more likely to provide pathogen identification results than using fungal culture. Male patients had a higher rate of onychomycosis overall; however, female patients had more non-dermatophyte mold onychomycosis caused by Aspergillus. Clinically diagnosed onychomycosis patients with a co-diagnosis of tinea pedis were more likely to test positive for onychomycosis by PCR (odds ratio [OR]: 4.2; 95% confidence interval [CI]: 2.7–6.4), histopathology (OR: 2.5; 95% CI: 2.0–3.1) and fungal culture (OR: 3.2; 95% CI: 1.5–6.6). Our results support the use of confirmatory laboratory testing when there is a clinical diagnosis of onychomycosis. [ABSTRACT FROM AUTHOR]

The three most commonly used methods for diagnosing non-dermatophyte mold (NDM) onychomycosis are culture, polymerase chain reaction (PCR), and histopathology. Toenail samples from 512 patients (1 sample/patient) with suspected onychomycosis were examined using all three diagnostic tests. A statistically significant association was found between PCR and histopathology results, as well as between fungal culture and histopathology results. All PCR-positive and culture-positive dermatophyte samples were confirmed by histopathology. However, 15/116 (12.9%) of culture-positive NDM samples had negative histopathology results, while all PCR-positive NDM samples were confirmed by histopathology. The overall rate of dermatophyte detection was higher using PCR compared to culture (38.9% vs. 11.7%); the lower rate of NDM detection by PCR (11.7% vs. 38.9%) could be attributed to the restriction of the assay design to seven pre-selected targets. When repeat sampling in the clinic is not possible, a combination of NDM detection by PCR and positive histopathology of hyphae may be a proxy for NDM infection, particularly where the NDM occurs without a concomitant dermatophyte. There was a high degree of correlation between negative PCR and negative histopathology. A negative PCR result with negative histopathology findings may be a reliable proxy for the diagnosis of non-fungal dystrophy. [ABSTRACT FROM AUTHOR]

ABSTRACT Background Objective Methods Results Conclusions Onychomycosis is a common nail disease that is often difficult to treat with a high risk of recurrence.To update our current understanding of the etiologic profile in pediatric patients with onychomycosis utilizing molecular diagnosis by polymerase chain reaction (PCR) combined with histopathologic examination.Records of 19,770 unique pediatric patients were retrieved from a single diagnostic laboratory in the United States spanning over a 9‐year period (March 2015 to April 2024). This cohort represents patients clinically suspected of onychomycosis seen by dermatologists and podiatrists. Dermatophytes, nondermatophyte molds (NDMs), and yeasts were identified by multiplex real‐time PCR corroborated by the demonstration of fungal invasion on histopathology.An average of 37.0% of all patients sampled were mycology‐confirmed to have onychomycosis. Most patients were between ages 11 and 16 years, and the rate of mycologically confirmed onychomycosis was significantly higher among the 6‐ to 8‐year (47.2%) and 9‐ to 11‐year (42.7%) age groups compared to the 0‐ to 5‐year (33.1%), 12‐ to 14‐year (33.2%), and 15‐ to 17‐year (36.7%) age groups. The majority of infections were caused dermatophytes (74.7%) followed by NDMs (17.4%). The Trichophyton rubrum complex represents the dominant pathogen with higher detection rates in the 6‐ to 11‐year‐olds. Fusarium was the most commonly isolated NDM with an increasing prevalence with age.Elementary school‐aged children have a higher risk of contracting onychomycosis which may be attributed to the onset of hyperhidrosis at puberty, use of occlusive footwear, nail unit trauma, and walking barefoot. Fusarium onychomycosis may be more prevalent than expected, and this may merit consideration of management strategies. [ABSTRACT FROM AUTHOR]