Clinical tests for onychomycosis

NewsBot · Oct 20, 2006

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Cost-effectiveness of diagnostic tests for toenail onychomycosis: a repeated-measure, single-blinded, cross-sectional evaluation of 7 diagnostic tests.
J Am Acad Dermatol. 2006 Oct;55(4):620-6
Lilly KK, Koshnick RL, Grill JP, Khalil ZM, Nelson DB, Warshaw EM

OBJECTIVE: Our purpose was to estimate and compare the cost-effectiveness of the most commonly used diagnostic tests for onychomycosis: potassium hydroxide preparation (KOH), interpreted both by a dermatologist (KOH-CLINIC) and a laboratory technician (KOH-LAB); KOH with dimethyl sulfoxide (KOH-DMSO) and with chlorazol black E (KOH-CBE), interpreted by a dermatologist; culture using dermatophyte test medium, culture with Mycobiotic and Inhibitory Mold Agar (Cx); and histopathologic analysis using periodic acid-Schiff stain (PAS).

METHODS: This was a repeated-measure, blinded, cross-sectional study conducted at the Minneapolis Veterans Affairs Medical Center. Inclusion criteria included: at least one toenail with 25% or more clinical disease, which was defined as subungual debris with onycholysis and/or onychauxis. Exclusion criteria included other nail dystrophies, use of oral antifungal medication for 2 months or longer within the past year, or topical ciclopirox lacquer within 6 weeks of enrollment. The main outcome measure was the cost-effectiveness (Medicare and non-Medicare costs) of 7 diagnostic tests. Sensitivity (at least 3 positive tests) was the unit of effectiveness.

RESULTS: Two hundred four participants were enrolled; their average age was 69.5 years and 95.5% were male. PAS was the most sensitive test (98.8%); it was statistically significantly more sensitive than all other diagnostic tests except KOH-CBE (94.3%). Dermatophye test medium was the least sensitive test (57.3%). KOH-CBE was statistically significantly more cost effective than any other test, with the exception of KOH-CLINIC and KOH-LAB. PAS was the least cost effective. LIMITATIONS: Test specificities were not evaluated.

CONCLUSION: KOH-CBE should be the test of choice for practitioners confident in interpreting KOH preparations because of its combination of high sensitivity and cost-effectiveness.
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Admin2 · Oct 20, 2006

onychomycosis

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NewsBot · Mar 10, 2007

Comparison of direct smear, culture and histology for the diagnosis of onychomycosis.
Australas J Dermatol. 2007 Feb;48(1):18-21
Karimzadegan-Nia M, Mir-Amin-Mohammadi A, Bouzari N, Firooz A

A sensitive and efficient diagnostic strategy is needed to confirm the clinical suspicion of onychomycosis. The purpose of this study was to compare the sensitivity of three most commonly used diagnostic methods for onychomycosis. Nail specimens of 96 patients with clinically suspected onychomycosis were evaluated using potassium hydroxide smear, culture and histology. A positive result of any of these tests was considered confirmatory for fungal infection and the sensitivity of each test as well as various combinations of them was calculated. The diagnosis of onychomycosis was confirmed in 47 patients (48.9%). Histology was the most sensitive single test for the diagnosis of onychomycosis, although its sensitivity (80.8%) was not statistically different from smear (76.5%). Both histology and smear were significantly more sensitive than culture (53.2%). The most sensitive combination of tests, smear plus histology, was 97.8% sensitive with 98% negative predictive value. In conclusion, direct smear combined with histological examination is the most sensitive diagnostic approach for onychomycosis
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NewsBot · Oct 2, 2009

Comparative study of nail sampling techniques in onychomycosis.
Shemer A, Davidovici B, Grunwald MH, Trau H, Amichai B.
J Dermatol. 2009 Jul;36(7):410-4.

Onychomycosis is a common problem. Obtaining accurate laboratory test results before treatment is important in clinical practice. The purpose of this study was to compare results of curettage and drilling techniques of nail sampling in the diagnosis of onychomycosis, and to establish the best technique and location of sampling. We evaluated 60 patients suffering from distal and lateral subungual onychomycosis and lateral subungual onychomycosis using curettage and vertical and horizontal drilling sampling techniques from three different sites of the infected nail. KOH examination and fungal culture were used for detection and identification of fungal infection. At each sample site, the horizontal drilling technique has a better culture sensitivity than curettage. Trichophyton rubrum was by far the most common pathogen detected by both techniques from all sampling sites. The drilling technique was found to be statistically better than curettage at each site of sampling, furthermore vertical drilling from the proximal part of the affected nail was found to be the best procedure for nail sampling. With each technique we found that the culture sensitivity improved as the location of the sample was more proximal. More types of pathogens were detected in samples taken by both methods from proximal parts of the affected nails.
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NewsBot · Dec 16, 2009

Microscopically differentiating dermatophytes from sock fibers.
Karan A, Alikhan A, Feldman SR.
J Am Acad Dermatol. 2009 Dec;61(6):1024-7.

BACKGROUND: Dermatophytes are responsible for a number of superficial fungal infections that affect millions worldwide. During microscopic observation a potassium hydroxide (KOH) fungal smear, various filamentous materials such as common textile fibers from socks can obfuscate proper discernment of dermatophytes.

OBJECTIVE: To differentiate dermatophytes from 9 common sock fibers. METHODS: Nine different textile fiber samples were microscopically analyzed by using a KOH direct smear test; their defining structural features were compared and contrasted with those of dermatophytes.

RESULTS: Although there are several similarities, sock fibers tend to have a non-septate, uniform structure which differentiates them from dermatophytes. Sock fibers are also significantly larger than dermatophytes and can be viewed better at lower magnifications. LIMITATIONS: There is a lack of sock samples with 100% textile fiber composition. Also, fibers were examined in a clean setting, without the detritus that normally accompanies dermatophytes in a clinical setting.

CONCLUSION: While textile fibers may be present in KOH preparations, their general appearance typically differs from that of dermatophytes; an observer who is familiar with these distinctions will be able to differentiate between the two.
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NewsBot · Jun 28, 2017

Meta-analysis of the utility of culture, biopsy, and direct KOH examination for the diagnosis of onychomycosis.
Velasquez-Agudelo V, Cardona-Arias JA
BMC Infect Dis. 2017 Feb 22;17(1):166. doi: 10.1186/s12879-017-2258-3.

BACKGROUND:
Onychomycosis is a highly prevalent disease worldwide. There is no standard test for its diagnosis, which remains costly, wasteful, and is sometimes delayed. The diagnostic tests for this disease are few and discordant. The objective was to evaluate the diagnostic validity, performance, and accuracy of culture, nail clipping with Periodic Acid-Schiff -PAS- staining (biopsy), and direct potassium hydroxide (KOH) examination for the study of onychomycosis.
METHODS:
A systematic review was conducted via meta-analysis using 5 databases and 21 search strategies. An ex ante protocol was applied with inclusion and exclusion criteria. Quality was assessed with the Quality Assessment of Diagnostic Accuracy Studies (QUADAS) tool, and the sensitivity, specificity, predictive values, likelihood ratios, diagnostic odds ratios, receiver operating characteristic (ROC) curves, and proportion of correctly diagnosed patients were evaluated with the meta-analysis of studies of evaluations of diagnostic and screening tests (Meta-DiSc) and Epidat using a random effects model.
RESULTS:
The efficiency or accuracy of the three tests is influenced by the methodological quality of the studies. These values are lower for KOH and culture and higher for biopsy in moderate quality studies.
CONCLUSION:
The diagnostic tests evaluated in this meta-analysis independently showed acceptable validity, performance, and efficiency, with nail clipping with PAS staining outperforming the other two tests.
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NewsBot · Sep 8, 2017

Onychomycosis Infections.
Aditya K. Gupta and Kerry-Ann Nakrieko
Journal of the American Podiatric Medical Association: July 2017, Vol. 107, No. 4, pp. 280-286.

Background: Mycological culture is the traditional method for identifying infecting agents of onychomycosis despite high false-negative results, slower processing, and complications surrounding nondermatophyte mold (NDM) infections. Molecular polymerase chain reaction (PCR) methods are faster and suited for ascertaining NDM infections.

Methods: To measure agreement between culture and PCR methods for identification of infecting species of suspected onychomycosis, single toenail samples from 167 patients and repeated serial samples from 43 patients with suspected onychomycosis were processed by culture and PCR for identification of 16 dermatophytes and five NDMs. Agreement between methods was quantified using the kappa statistic (κ).

Results: The methods exhibited fair agreement for the identification of all infecting organisms (single samples: κ = 0.32; repeated samples: κ = 0.38). For dermatophytes, agreement was moderate (single samples: κ = 0.44; repeated samples: κ = 0.42). For NDMs, agreement was poor with single samples (κ = 0.16) but fair with repeated samples (κ = 0.25). Excluding false-negative reports from analyses improved agreement between methods in all cases except the identification of NDMs from single samples.

Conclusions: Culture was three or four times more likely to report a false-negative result compared with PCR. The increased agreement between methods observed by excluding false-negative reports statistically clarifies and highlights the major discord caused by false-negative cultures. The increased agreement of NDM identification from poor to fair with repeated sampling along with their poor agreement in the single samples, with and without false-negatives, affirms the complications of NDM identification and supports the recommendation that serial samples help confirm the diagnosis of NDM infections.
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NewsBot · Apr 18, 2018

Performance of mycology and histopathology tests for the diagnosis of toenail onychomycosis due to filamentous fungi: Dermatophyte and non-dermatophyte moulds.
Lavorato FG et al
Mycoses. 2017 Sep;60(9):587-593.

Improvement of laboratory diagnosis of onychomychosis is important so that adequate treatment can be safely implemented. To evaluate and compare the performance of mycological and histopathological examinations in onychomycoses caused by dermatophyte and non-dermatophyte moulds. Patients with lateral/distal subungual onychomycosis in at least one hallux were enrolled in the protocol and assessed via mycological and histopathological tests. The isolation of filamentous fungi was considered the gold standard. Test performance was evaluated through sensitivity, specificity and positive and negative predictive values. A total of 212 patients were enrolled in the study. Direct microscopy (DM) was positive in 57.5% patients, and cultures in 34.4%. Among these patients, 23.3% were positive for dermatophytes, with Trichophyton rubrum the most frequently isolated, and 86.3% were positive for non-dermatophytes, with Neoscytalidium dimidiatum predominance. Histopathology was positive in 41.0% samples. Direct microscopy showed better sensitivity for non-dermatophyte moulds (P=.000) and nail clipping was more specific for dermatophyte (P=.018). Histopathology of the distal nail plate is a valuable complementary tool for the diagnosis of onychomycosis caused by dermatophytes and direct microscopy is especially useful for non-dermatophyte molds.
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NewsBot · Sep 2, 2020

A prospective study using image analysis to assess the efficacy of a topical treatment kit for mild onychomycosis
Nancy Khammo et al
Mycoses. 2020 Feb;63(2):233-240

Background: Onychomycosis is a fungal infection of the nails and is one of the most common dermatological infections worldwide. Infection occurs predominantly in the nails of the feet and if left untreated patients, particularly in at-risk populations, can develop more serious complications, including pain, fissuring and secondary infections. Fungal infections are also contagious and may spread to other nails or to family members. Topical treatments can be effective for mild cases of the disease and typically have fewer contraindications. However, generation of robust efficacy data for topical therapies is often hindered by the difficulties associated with monitoring progression of mild onychomycosis using the conventional methods of mycological culture to obtain confirmation of podiatrist assessments.

Objectives: The aim of this study was to demonstrate image analysis as an effective method to monitor progression of fungal nail infections.

Methods: A novel digital image analysis technique was used to evaluate improvement in the visual signs of onychomycosis, when using a topical treatment kit for mild fungal nail infections in 60 participants over a 280-day period.

Results: Image analysis demonstrated a significant (P < .0001) reduction from baseline of the affected nail area throughout the study period, results which were also perceived by the subjects themselves. Use of the treatment kit also limited the deterioration of the infection and prevented transmission to other nails.

Conclusions: Image analysis was established as a viable method to monitor the progression of fungal nail infections over long periods and demonstrate a clinical benefit following treatment.
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NewsBot · Sep 26, 2022

Clinical Clues to Differentiate between Dermatophyte Onychomycosis (DP-OM) and Dermatophytoma-Like Traumatic Onychodystrophy (DP-TO)
Sumanas Bunyaratavej et al
Biomed Res Int. 2022 Sep 9;2022:8519376

Background: Dermatophytoma is a recalcitrant condition of onychomycosis (OM). It presents as a white- or yellow-colored fungal mass that appears linear/triangular or round on a nail plate. Traumatic onychodystrophy (TO) can present with dermatophytoma-like lesions. Typically, OM and TO are not clinically distinguishable. Mycological testing is the gold standard for differentiating these disorders.

Objectives: This study is aimed at differentiating between the clinical and dermoscopic factors related to dermatophytoma onychomycosis (DP-OM) and dermatophytoma-like traumatic onychodystrophy (DP-TO).

Methods: A retrospective study was conducted of patients with dermatophytoma-like nail lesions who visited the Siriraj Nail Clinic between January 2010 and July 2020. The diagnosis of DP-OM was made by direct microscopy, fungal cultures, and histopathology of nail clippings.

Results: A total of 36 nails were included in the study. Thirteen nails were DP-OM, and 23 nails were DP-TO. The demographic data and risk factors for the 2 groups were not significantly different. Dermatophytoma lesions were found on the lateral side of nails in 12 cases of DP-OM (92.3%) and 11 cases of DP-TO (47.8%; P = 0.008). DP-OM was associated with longitudinal striae adjacent to dermatophytoma (69.2% vs. 30.4%; P = 0.024), sulfur-nugget-like subungual debris (23.1% vs. 0%; P = 0.040), and scale on the ipsilateral foot (69.2% vs. 8.7%; P < 0.001). DP-TO was associated with a homogenous, whitish discoloration (47.8% vs. 7.7%; P = 0.014) and a sharp edge of the onycholytic area (43.5% vs. 0%; P = 0.005).

Conclusions: The lateral location of dermatophytoma, adjacent striae, sulfur-nugget-like debris, and scale on the ipsilateral foot were significantly associated with DP-OM. Dermoscopic examination (dorsal and hyponychium views) and foot examination are beneficial for distinguishing between DP-OM and DP-TO.
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NewsBot · Aug 14, 2023

Microbiological culture combined with PCR for the diagnosis of onychomycosis: Descriptive analysis of 121 patients
David Navarro-Pérez et al
Mycoses. 2023 Aug 13

Background: Onychomycosis is the most common nail pathology, involving various pathogens such as dermatophytes, moulds and yeasts.

Objective: The objective of this study was to observe the prevalence of onychomycosis, analyse the most appropriate diagnostic test, and assess the distribution of pathogens based on age, sex, quarter of the year, duration of symptoms and previous treatment.

Methods: Retrospectively, mycological culture and PCR data and results were collected from 121 patients.

Results: Of the 121 samples, 57% (69/121) tested positive when both microbiological study techniques were combined. The prevalence of onychomycosis was higher when PCR was performed (52.1%) compared to microbiological culture (33.1%). Among the 81 samples negative by microbiological culture, 31 were positive by PCR. Similarly, of the 58 samples negative by PCR, eight were positive by microbiological culture. Diagnostic accuracy data (with 95% confidence intervals) for PCR, using microbiological culture as the gold standard, were as follows: sensitivity of 0.8, specificity of 0.62, positive predictive value of 0.51 and negative predictive value of 0.86. The most frequently identified pathogen was Trichophyton rubrum, and the hallux nail plate was the most commonly affected location. However, no statistically significant associations were found between sex, age, quarter of the year and affected area with culture and PCR results.

Conclusion: Combining microbiological culture and PCR can increase the detection rate of onychomycosis and help avoid false-negative results.
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