Diagnosing dermatomycosis in general practice

Background. Diagnosing dermatomycosis from a clinical image is not always e asy. Microscopy of a potassium hydroxide preparation (KOH-test) and culturi ng are seldomly used in general practice. Cyanoacrylate surface skin scrapi ng (CSSS) is a new diagnostic tool that may be useful and simple. Objectives. We aimed to investigate the diagnostic value of signs and sympt oms, the KOH-test and the CSSS, in patients with erythematosquamous skin le sions, using the culture as the gold standard. Our goal is to formulate an optimal algorithm for the diagnosis of mycosis, based on one or more of the se tests and including both optimal accuracy and costs. Methods. Scales from 148 consecutive general practice patients were tested using a KOH-test, CSSS and culture. Clinical data were collected using a qu estionnaire. Results. Twenty-six (18%) positive fungal cultures were identified. The sen sitivity of the clinical diagnosis was 81% and its specificity 45%; for the KOH-test these figures were 12 and 93% respectively; and for the CSSS, 62 and 88%, respectively. The positive predictive value of the clinical diagno sis was 24% and the negative predictive value 92%; for the KOH-test these f igures were 25 and 83%, respectively, and for the CSSS, 52 and 92%, respect ively. Determining CSSS in all patients proved to be the most accurate poli cy (accuracy = 83%). The likelihood ratio of CSSS in all patients was 5.17 for a positive test result and 0.43 for a negative test result. An approach in which CSSS is obtained in only those patients whom the physician consid ers by clinical examination to have dermatomycosis, with no testing in othe r patients, results in positive and negative likelihood ratios of 4.69 and 0.56, respectively. Such a policy would result in an overall sensitivity of 50%, a specificity of 89%, a positive predictive value of 50% and a negati ve predictive value of 89%. Discussion. The clinical picture of dermatomycosis is not very reliable. Th e combination of a clinical judgement if this is negative and an additional CSSS in the case of a positive clinical judgement provides us with the bes t cost-benefit ratio, if both diagnostic accuracy and logistic consideratio ns are taken into consideration.