Diagnosis of Onychomycosis: From Conventional Techniques and Dermoscopy to Artificial Intelligence

Onychomycosis in the US Pediatric Population-An Emphasis on Fusarium Onychomycosis

BACKGROUND

Onychomycosis is a common nail disease that is often difficult to treat with a high risk of recurrence.

OBJECTIVE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Epidemiology of Onychomycosis in the United States Characterized Using Molecular Methods, 2015-2024

Onychomycosis is a recalcitrant fungal infection of the nail unit that can lead to secondary infections and foot complications. Accurate pathogen identification by confirmatory testing is recommended to improve treatment outcomes. In this study, we reviewed the records of 710,541 patients whose nail specimens were sent to a single molecular diagnostic laboratory between 2015 and 2024. PCR testing revealed a more comprehensive spectrum of pathogens than previously reported, which was corroborated by the demonstration of fungal invasion on histopathology. Consistent with our current understanding, the T. rubrum complex (54.3%) are among the most common pathogens; however, a significant portion of mycology-confirmed diagnoses were caused by the T. mentagrophytes complex (6.5%), Aspergillus (7.0%) and Fusarium (4.5%). Females were significantly more likely to be infected with non-dermatophytes molds (NDMs; OR: 2.0), including Aspergillus (OR: 3.3) and Fusarium (OR: 2.0), and yeasts (OR: 1.5), including Candida albicans (OR: 2.0) and C. parapsilosis (OR 1.6), than males. The T. mentagrophytes complex became more prevalent with age, and conversely the T. rubrum complex became less prevalent with age. Patients aged ≥65 years also demonstrated a higher likelihood of contracting onychomycosis caused by NDMs (OR: 1.6), including Aspergillus (OR: 2.2), Acremonium (OR: 3.5), Scopulariopsis (OR: 2.9), Neoscytalidium (OR: 3.8), and yeasts (OR: 1.8), including C. albicans (OR: 1.9) and C. parapsilosis (OR: 1.7), than young adults. NDMs (e.g., Aspergillus and Fusarium) and yeasts were, overall, more likely to cause superficial onychomycosis and less likely to cause dystrophic onychomycosis than dermatophytes. With regards to subungual onychomycosis, Aspergillus, Scopulariopsis and Neoscytalidium had a similar likelihood as dermatophytes. The advent of molecular diagnostics enabling a timely and accurate pathogen identification can better inform healthcare providers of appropriate treatment selections and develop evidence-based recommendations.

Artificial Intelligence in the Diagnosis of Onychomycosis-Literature Review

Onychomycosis is a common fungal nail infection that is difficult to diagnose due to its similarity to other nail conditions. Accurate identification is essential for effective treatment. The current gold standard methods include microscopic examination with potassium hydroxide, fungal cultures, and Periodic acid-Schiff biopsy staining. These conventional techniques, however, suffer from high turnover times, variable sensitivity, reliance on human interpretation, and costs. This study examines the potential of integrating AI (artificial intelligence) with visualization tools like dermoscopy and microscopy to improve the accuracy and efficiency of onychomycosis diagnosis. AI algorithms can further improve the interpretation of these images. The review includes 14 studies from PubMed and IEEE databases published between 2010 and 2024, involving clinical and dermoscopic pictures, histopathology slides, and KOH microscopic images. Data extracted include study type, sample size, image assessment model, AI algorithms, test performance, and comparison with clinical diagnostics. Most studies show that AI models achieve an accuracy comparable to or better than clinicians, suggesting a promising role for AI in diagnosing onychomycosis. Nevertheless, the niche nature of the topic indicates a need for further research.

Global prevalence of onychomycosis in general and special populations: An updated perspective

BACKGROUND

Onychomycosis is a chronic nail disorder commonly seen by healthcare providers; toenail involvement in particular presents a treatment challenge.

OBJECTIVE

To provide an updated estimate on the prevalence of toenail onychomycosis.

METHODS

We conducted a literature search using PubMed, Embase and Web of Science. Studies reporting mycology-confirmed diagnoses were included and stratified into (a) populations-based studies, and studies that included (b) clinically un-suspected and (c) clinically suspected patients.

RESULTS

A total of 108 studies were included. Based on studies that examined clinically un-suspected patients (i.e., with or without clinical features suggestive of onychomycosis), the pooled prevalence rate of toenail onychomycosis caused by dermatophytes was 4% (95% CI: 3-5) among the general population; special populations with a heightened risk include knee osteoarthritis patients (RR: 14.6 [95% CI: 13.0-16.5]), chronic venous disease patients (RR: 5.6 [95% CI: 3.7-8.1]), renal transplant patients (RR: 4.7 [95% CI: 3.3-6.5]), geriatric patients (RR: 4.7 [95% CI: 4.4-4.9]), HIV-positive patients (RR: 3.7 [95% CI: 2.9-4.7]), lupus erythematosus patients (RR: 3.1 [95% CI: 1.2-6.3]), diabetic patients (RR: 2.8 [95% CI: 2.4-3.3]) and hemodialysis patients (RR: 2.8 [95% CI: 1.9-4.0]). The prevalence of onychomycosis in clinically suspected patients was significantly higher likely due to sampling bias. A high degree of variability was found in a limited number of population-based studies indicating that certain pockets of the population may be more predisposed to onychomycosis. The diagnosis of non-dermatophyte mould onychomycosis requires repeat sampling to rule out contaminants or commensal organisms; a significant difference was found between studies that performed single sampling versus repeat sampling. The advent of PCR diagnosis results in improved detection rates for dermatophytes compared to culture.

CONCLUSION

Onychomycosis is an underrecognized healthcare burden. Further population-based studies using standardized PCR methods are warranted.

Artificial Intelligence: Exploring utility in detection and typing of fungus with futuristic application in fungal cytology

Artificial Intelligence (AI) is an emerging, transforming and revolutionary technology that has captured attention worldwide. It is translating research into precision oncology treatments. AI can analyse large or big data sets requiring high-speed specialized computing solutions. The data are big in terms of volume and multimodal with the amalgamation of images, text and structure. Machine learning has identified antifungal drug targets, and taxonomic and phylogenetic classification of fungi based on sequence analysis is now available. Real-time identification tools and user-friendly mobile applications for identifying fungi have been discovered. Akin to histopathology, AI can be applied to fungal cytology. AI has been fruitful in cytopathology of the thyroid gland, breast, urine and uterine cervical lesions. AI has a huge scope in fungal cytology and would certainly bear fruit with its accuracy, reproducibility and capacity for handling big data. The purpose of this systematic review was to highlight the AI's utility in detecting fungus and its typing with a special focus on future application in fungal cytology. We also touch upon the basics of AI in brief.

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.

The Role of Trypan Blue as a Conventional and Fluorescent Dye for the Diagnosis of Superficial Mycoses by Potassium Hydroxide (KOH) Testing

Direct microscopic examination of samples using potassium hydroxide (KOH) is a fast, simple, and inexpensive method to confirm clinical suspicion of superficial mycosis. However, the lack of color contrast in this test makes it difficult to separate any fungal structures from artifacts. The sensitivity of the KOH mount technique may be enhanced using both fluorochromes and conventional stains that highlight the fungal structures when observed under fluorescence microscopy and bright-field, respectively. Here we study the possibility of using Trypan Blue (TB), an azo dye which is often used as a live/dead marker, in the diagnosis of superficial mycoses by KOH testing. TB at 0.01% displayed a fluorescent staining pattern similar to that of Calcofluor White (CFW), the conventional cell wall fluorophore. Furthermore, by adjusting the TB concentration to 0.1-0.3%, in addition to maintaining the fluorescent staining pattern, the fungal elements were stained in blue under bright-field microscopy. Thus, we demonstrate for the first time that TB has the unique property as a fungal stain that can be used in both bright-field and fluorescence microscopy for diagnosis of superficial mycoses by direct microscopic examination.

Retrospective Analysis of Liver Enzyme Abnormalities in Patients Prescribed Terbinafine and Itraconazole for Onychomycosis

Introduction Onychomycosis (OM) is defined as a nail fungal infection. Its prevalence increases with advancing age. Human-to-human transmission makes it a serious public health risk. Although OM is not a life-threatening disease, it has a detrimental effect on patients' quality of life. Due to the long therapy duration and potential side effects of systemic antifungal medicines, physicians may be reluctant to treat OM orally. In this study, we aimed to evaluate the effect of terbinafine and itraconazole on liver transaminases, the side effects of these treatments, and patients' adherence to systemic treatment of OM. Methods This is a retrospective study conducted in our dermatology department (Ordu University, Ordu) between June 2020 and October 2021. Hospital records were analyzed, and patients with the diagnosis of tinea unguium (ICD code B35.1) were investigated. Patients who were prescribed terbinafine or itraconazole were included in the study. Following a clinical diagnosis of OM, the researchers first tried to confirm it through direct microscopic examination with potassium hydroxide (KOH). If the direct microscopic examination was negative but the suspicion about OM continued, confirmation was done through a fungal culture. Results This study included 735 patients, of whom 409 (55.6%) were female and 326 (44.4%) were male. The research covered all of the patients who were given one of these two medications. To find patients who could apply to other hospitals, the Turkish National Healthcare System was checked in addition to hospital information. To identify patients who could apply to other healthcare institutions, all hospitals share their data with this national healthcare system. Terbinafine was used by 433 patients (76.4%), 75 patients (13.2%), and 37 patients (6.5%), respectively, for one, two, and three months. A total of 119 patients (70.8%) took itraconazole for a month, 32 patients (19%) took it for two months, and four patients (2.33%) took it for three months. At the end of the first month, the proportion of the patients with elevated aspartate transaminase (AST) levels was 5.2% for terbinafine and 0% for itraconazole. Eighteen (8.4%) patients with terbinafine had elevated alanine aminotransferase (ALT) levels, and four patients (7.5%) who were on itraconazole treatment had high ALT levels. None of the patients reported cutaneous adverse drug reactions, gastrointestinal disturbances, or headaches due to OM treatment. Also, no patients discontinued treatment because of hepatotoxicity. Conclusion In this study, none of the patients discontinued the treatment because of hepatotoxicity. According to the results of this study, oral terbinafine and itraconazole can be used with close follow-up. Baseline and regular laboratory monitoring for AST and ALT should be done to monitor liver toxicity with terbinafine and itraconazole. Besides, we did not observe other side effects like cutaneous or cardiac side effects or drug-drug interactions.

Clinical evaluation of a dermatophyte RT-PCR assay and its impact on the turn-around-time: A prospective study

Onychomycosis is an important public health problem whose prevalence continues to grow and impact public health at several levels. Nevertheless, today the main diagnostic methods used in routine practice have many drawbacks. The aim of this study was to evaluate, for the first time, the clinical performance of a new multiplex polymerase chain reaction (PCR) (Novaplex®) in the identification of the causative agent on nail samples, and its impact on the turnaround time, compared to our traditional laboratory methods. From June 2022 to December 2022, all nail samples sent to our laboratory for suspected onychomycosis were included in this prospective study. We collected for each sample the results obtained with the Novaplex® PCR method and with the traditional direct microscopy examination and culture. Each discordant result was checked using a third method, which is another PCR method (DermaGenius® kit) as a resolver. For culture-positive samples, a turnaround time was calculated and compared to the one obtained with the Novaplex® method. A total of 131 samples were included. Among them, 5 were positive (3.8%) on direct microscopy, 33 were positive (25.2%) after culture, and 98 were negative (74.8%). All positive (n = 33) and negative (n = 69) cultures were also positive/negative with the Novaplex® PCR. Twenty-nine samples were positive with the Novaplex® method but negative with culture (discordant results). The percentage agreement between the culture and the Novaplex® methods was 77.9% (102 out of 131). While tested with the resolver (DermaGenius® PCR), 28 out of 29 discordant results were similarly found positive. The percentage agreement between the two PCR methods (Novaplex® and DermaGenius®) was 96.6%. The Novaplex® PCR method evaluated proved to be very reliable and allowed the direct identification of 62 out of 131 positive samples (47.3%) with the following distribution: 79.0% of Trichophyton rubrum complex, 11.3% of Trichophyton mentagrophytes complex, 6.5% of both Trichophyton rubrum complex and Trichophyton mentagrophytes complex, and 3.2% of Candida albicans. The median time [± 95% CI] for positive culture (between incubation and validation of the final identification) was 15 [12-23] days, while the turnaround time for the Novaplex® method adapted to our clinical laboratory routine is ≤7 days. Laboratory confirmation of onychomycosis is crucial and should always be obtained before starting treatment. The evaluated PCR method offered a rapid, reliable, robust, and inexpensive method of identification of the causative agent compared to traditional methods.

Applications of Reflectance Confocal Microscopy in the Diagnosis of Fungal Infections: A Systematic Review

Cutaneous and adnexal fungal infections are typically diagnosed with potassium hydroxide (KOH) skin scrapings, fungal cultures, and Periodic acid-Schiff (PAS) biopsy staining. All three current methods of fungal diagnosis require sample processing and turnover time which leads to a delay in diagnosis. Reflectance confocal microscopy (RCM) is a non-invasive, in vivo skin imaging technology that provides real-time dermatologic diagnoses. We present an updated systematic review of the applications of RCM in diagnosing fungal infections in an effort to explore the utility of RCM as an adjunct clinical tool in detecting cutaneous and adnexal fungi We systematically searched the MEDLINE (via PubMed) for studies published from January 2000 to October 2022 that described the utility of RCM in the setting of fungal infections. Of the 25 studies that met the inclusion criteria, 202 patients were included. The following information on the application of RCM in the setting of fungal infections was extracted from each study, if reported: study type, year published, number of patients included, diagnosis/diagnostic methods, and RCM description. Concordant within all included studies, fungal infections presented on RCM as bright, linear, branching, filamentous structures at the level of stratum corneum. A limitation of this review is that 11 of 25 studies were case reports (n = 1). Larger scale studies should be conducted to explore the utility of RCM in diagnosing fungal infections and to enrich the RCM descriptions of specific fungal conditions.

Reflectance Confocal Microscopy in the Diagnosis of Onychomycosis: A Systematic Review

Accurately diagnosing onychomycosis is vital, as therapy is time-consuming and accompanied by multiple adverse effects. Reflectance confocal microscopy (RCM), in contrast to traditional mycological testing, is a noninvasive, point-of-care tool that can rapidly identify fungal lesions. This systematic review aims to understand the utility of RCM in evaluating onychomycosis and follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A systematic search of four databases was conducted. A total of five articles-three prospective cohort studies and two case reports-which reported RCM findings in nails clinically suspicious for onychomycosis were analyzed. Fungal hyphae or spores were visualized on RCM in 67 (81.7%) of the 82 mycologically confirmed cases of onychomycosis. Terms used to describe hyphae included bright, linear, lengthy, thready-like, branching and filamentous. Spores were described as bright, roundish structures with high reflection. The three cohort studies demonstrated RCM had a sensitivity of 52.9-91.7, a specificity of 57.58-90.2%, a positive predictive value of 61.1-88.6% and a negative predictive value of 68.0-90.5%. In conclusion, existing studies demonstrate how RCM can assist the diagnosis of onychomycosis at the bedside. Larger studies incorporating multiple testing modalities to confirm the diagnosis of onychomycosis are warranted to further explore the diagnostic utility of RCM.

Updated Perspectives on the Diagnosis and Management of Onychomycosis

Onychomycosis is the most common nail disease encountered in clinical practice and can cause pain, difficulty with ambulation, and psycho-social problems. A thorough history and physical examination, including dermoscopy, should be performed for each patient presenting with nail findings suggestive of onychomycosis. Several approaches are available for definitive diagnostic testing, including potassium hydroxide and microscopy, fungal culture, histopathology, polymerase chain reaction, or a combination of techniques. Confirmatory testing should be performed for each patient prior to initiating any antifungal therapies. There are several different therapeutic options available, including oral and topical medications as well as device-based treatments. Oral antifungals are generally recommended for moderate to severe onychomycosis and have higher cure rates, while topical antifungals are recommended for mild to moderate disease and have more favorable safety profiles. Oral terbinafine, itraconazole, and griseofulvin and topical ciclopirox 8% nail lacquer, efinaconazole 10% solution, and tavaborole 5% solution are approved by the Food and Drug Administration for treatment of onychomycosis in the United States and amorolfine 5% nail lacquer is approved in Europe. Laser treatment is approved in the United States for temporary increases in clear nail, but clinical results are suboptimal. Oral fluconazole is not approved in the United States for onychomycosis treatment, but is frequently used off-label with good efficacy. Several novel oral, topical, and over-the-counter therapies are currently under investigation. Physicians should consider the disease severity, infecting pathogen, medication safety, efficacy and cost, and patient age, comorbidities, medication history, and likelihood of compliance when determining management plans. Onychomycosis is a chronic disease with high recurrence rates and patients should be counseled on an appropriate plan to minimize recurrence risk following effective antifungal therapy.

Diagnosing Onychomycosis: What's New?

An overview of the long-established methods of diagnosing onychomycosis (potassium hydroxide testing, fungal culture, and histopathological examination) is provided followed by an outline of other diagnostic methods currently in use or under development. These methods generally use one of two diagnostic techniques: visual identification of infection (fungal elements or onychomycosis signs) or organism identification (typing of fungal genus/species). Visual diagnosis (dermoscopy, optical coherence tomography, confocal microscopy, UV fluorescence excitation) provides clinical evidence of infection, but may be limited by lack of organism information when treatment decisions are needed. The organism identification methods (lateral flow techniques, polymerase chain reaction, MALDI-TOF mass spectroscopy and Raman spectroscopy) seek to provide faster and more reliable identification than standard fungal culture methods. Additionally, artificial intelligence methods are being applied to assist with visual identification, with good success. Despite being considered the 'gold standard' for diagnosis, clinicians are generally well aware that the established methods have many limitations for diagnosis. The new techniques seek to augment established methods, but also have advantages and disadvantages relative to their diagnostic use. It remains to be seen which of the newer methods will become more widely used for diagnosis of onychomycosis. Clinicians need to be aware of the limitations of diagnostic utility calculations as well, and look beyond the numbers to assess which techniques will provide the best options for patient assessment and management.

Transmission of Onychomycosis and Dermatophytosis between Household Members: A Scoping Review

Onychomycosis is a common fungal infection of the nail, caused by dermatophytes, non-dermatophytes, and yeasts. Predisposing factors include older age, trauma, diabetes, immunosuppression, and previous history of nail psoriasis or tinea pedis. Though many biological risk factors have been well characterized, the role of the environment has been less clear. Studies have found evidence of transmission in 44% to 47% of households with at least one affected individual, but the underlying mechanisms and risk factors for transmission of onychomycosis between household members are incompletely understood. A scoping literature review was performed to characterize and summarize environmental risk factors involved in the transmission of onychomycosis within households. A total of 90 papers met the inclusion criteria, and extracted data was analyzed in an iterative manner. Shared household surfaces may harbor dermatophytes and provide sources for infection. Shared household equipment, including footwear, bedding, and nail tools, may transmit dermatophytes. The persistence of dermatophytes on household cleaning supplies, linen, and pets may serve as lasting sources of infection. Based on these findings, we provide recommendations that aim to interrupt household transmission of onychomycosis. Further investigation of the specific mechanisms behind household spread is needed to break the cycle of transmission, reducing the physical and social impacts of onychomycosis.

Diagnosing onychomycosis: A step forward?

BACKGROUND AND AIMS

There are a number of available methods for diagnosing onychomycosis, but more emerge as technology advances. This review briefly discusses the common diagnostic methods, the use of artificial intelligence (AI) as a diagnostic tool in dermatology as a whole, and then examines research on the use of AI for diagnosing onychomycosis. The studies discussed implemented convolutional neural networks (CNNs) to examine datasets of images of entire nails or histological images and then used the information learned from those datasets to make a diagnostic decision of onychomycosis or not.

RESULTS

Results: It was found that, on average, AI were able to diagnose onychomycosis from the images provided at an equivalent level as human dermatologists. However, there are a number of clear limitations for using AI in this manner. The AI models implemented relied solely on images and therefore were limited by image quality. As only images were examined, other clinical data were not taken into consideration, which could be important to the diagnostic outcome.

CONCLUSION

Conclusion: In conclusion, although AI can be a very helpful tool in the diagnostic process by increasing efficiency and reducing costs, it still requires the precision and expertise of professional dermatologists to be used optimally.