Weinberg Jeffrey M, Koestenblatt Evelyn K, Tutrone William D, Tishler Hillarie R, Najarian Lily
Department of Dermatology at St Luke's-Roosevelt Hospital Center, New York, NY 10025, USA.
J Am Acad Dermatol. 2003 Aug;49(2):193-7. doi: 10.1067/s0190-9622(03)01480-4.
Onychomycosis is a common problem seen in clinical practice. Given the differential diagnosis of dystrophic nails, it is helpful to obtain a definitive diagnosis of dermatophyte infection before the initiation of antifungal therapy. Potassium hydroxide (KOH) preparation and fungal culture, which are typically used in the diagnosis of these infections, often yield false-negative results. Recent reports have suggested that nail plate biopsy using periodic acid-Schiff (PAS) (Bx/PAS) stain may be a very sensitive technique for the diagnosis of onychomycosis.
The purpose of this study was to compare KOH preparation, culture, Bx/PAS stain, and calcofluor white (CW) stain in the diagnosis of onychomycosis and to determine their sensitivity and specificity.
We evaluated 105 patients with suspected onychomycosis using 4 diagnostic methods: KOH preparation, culture, Bx/PAS, and CW stain. CW stain binds to cellulose and chitin, and fluoresces when exposed to UV radiation. It is a highly sensitive and specific technique for the detection of dermatophytes. To determine the clinical usefulness and performance characteristics of each test, CW was chosen as the gold standard for statistical analysis.
Of the patients, 93 had at least 1 of the 4 diagnostic methods positive for the presence of organisms. The following were calculated for each test: sensitivity; specificity; positive predictive value; and negative predictive value. The sensitivities of each of the techniques were as follows: KOH 80%; Bx/PAS 92%; and culture 59%. Both KOH and Bx/PAS methods were more sensitive than culture (P =.00002). Bx/PAS was also more sensitive than KOH (P =.03). The specificities were as follows: KOH 72%; Bx/PAS 72%; and culture 82%. The positive predictive value calculated for the different techniques were: KOH 88%; Bx/PAS 89.7%; and culture 90%. In terms of negative predictive value, the results were: KOH 58%; Bx/PAS 77%; and culture 43%.
Bx/PAS is the most sensitive method for the diagnosis of onychomycosis. It is also superior to the other methods in its negative predictive value. It is indicated if other methods are negative and clinical suspicion is high, and potentially is the single method of choice for the evaluation of onychomycosis.
甲真菌病是临床实践中常见的问题。鉴于甲营养不良的鉴别诊断，在开始抗真菌治疗前获得皮肤癣菌感染的明确诊断很有帮助。常用于诊断这些感染的氢氧化钾（KOH）制片和真菌培养常常产生假阴性结果。最近的报告表明，使用过碘酸希夫（PAS）染色的甲板活检（Bx/PAS）可能是诊断甲真菌病的一种非常敏感的技术。
本研究的目的是比较KOH制片、培养、Bx/PAS染色和荧光钙白（CW）染色在诊断甲真菌病中的效果，并确定它们的敏感性和特异性。
我们使用4种诊断方法评估了105例疑似甲真菌病的患者：KOH制片、培养、Bx/PAS和CW染色。CW染色与纤维素和几丁质结合，并在紫外线照射下发出荧光。它是检测皮肤癣菌的一种高度敏感和特异的技术。为了确定每种检测方法的临床实用性和性能特征，选择CW作为统计分析的金标准。
在这些患者中，93例至少有4种诊断方法中的1种检测到有生物体存在。计算了每种检测方法的以下指标：敏感性；特异性；阳性预测值；阴性预测值。每种技术的敏感性如下：KOH为80%；Bx/PAS为92%；培养为59%。KOH和Bx/PAS方法均比培养更敏感（P = 0.00002）。Bx/PAS也比KOH更敏感（P = 0.03）。特异性如下：KOH为72%；Bx/PAS为72%；培养为82%。不同技术计算出的阳性预测值为：KOH为88%；Bx/PAS为89.7%；培养为90%。就阴性预测值而言，结果为：KOH为58%；Bx/PAS为77%；培养为43%。
Bx/PAS是诊断甲真菌病最敏感的方法。其阴性预测值也优于其他方法。如果其他方法为阴性且临床怀疑度高，则推荐使用该方法，它可能是评估甲真菌病的单一首选方法。
