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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
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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.
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
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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
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.
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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.
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.
Clinical tests for onychomycosis
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