Clinical Diagnosis and Laboratory Testing of Abnormal Appearing Toenails: A Retrospective Assessment of Confirmatory Testing for Onychomycosis in the United States, 2022-2023.

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.

A comparison of results from two mycology laboratories for the diagnosis of onychomycosis: a study of 85 cases in a geriatric population.

An investigative study was performed to compare the results from two mycology laboratories for the diagnosis of onychomycosis in a geriatric population and to determine the possible pharmacologic treatments based on the two laboratories' results. In this study, 85 cases of suspected onychomycosis involving men and women 65 years and older from a nursing home setting in South Florida were used. Samples were taken from the hallux toenail and sent to two different mycology laboratories for fluorescent potassium hydroxide preparation and microscopic examination of a fungal culture. Of the 85 cases studied, the two mycology laboratories reported similar potassium hydroxide preparation results for 58.8% of the patients and similar fungal culture results for genus and species identification for 37.6% of the patients. When the potassium hydroxide preparation and fungal culture results were combined, the two mycology laboratories reported similar results for only 27.1% of the patients. As a result of the two mycology laboratories' findings, the possible US Food and Drug Administration-approved pharmacologic treatments may differ for 43.5% of the patients studied. The discrepancy between the two independent laboratories leaves physicians to question the reproducibility of fluorescent potassium hydroxide preparation and fungal culture analysis in a geriatric patient population for the diagnosis of onychomycosis.

Scanning electron microscope imaging of onychomycosis.

Although scanning electron microscope technology has been used for more than 60 years in many fields of medical research, no studies have focused on obtaining high-resolution microscopic images of onychomycosis of the toenail caused by Trichophyton rubrum in a geriatric population. To provide new insight into the intricate structure and behavior of chronic toenail onychomycosis, we produced three-dimensional images of onychomycosis obtained from two geriatric patients with confirmed growth of T rubrum. The photomicrographs illustrate the pervasive integration and penetration of the fungus hyphal elements, underscoring the clinical difficulty of obtaining rapid treatment of fungal infections in the distal and lateral subungual space of the human toenail. Although the scanning electron microscope may not be a practical diagnostic tool for most physicians, it remains invaluable for the researcher to obtain insight into the spatial orientation, behavior, and appearance of onychomycosis.