Onychomycosis: the development of a clinical diagnostic aid for toenail disease. Part I. Establishing discriminating historical and clinical features

Background The ideal method for diagnosing onychomycosis is unclear. Mycological investigation is currently the method of choice, although there is a false-negative culture rate of at least 30%. Objectives To establish a clinical diagnostic aid which may be used alongside laboratory-based mycological tests and in epidemiological studies. Methods Patients with nail disease (n = 209) were enrolled in the study. The examining clinician completed a questionnaire containing four historical questions and 21 questions related to the clinical findings. All patients had samples taken for mycological analysis. The gold standard for the diagnosis of onychomycosis was a positive result on both direct microscopy and culture of nail samples. Following exclusions, questionnaire responses from 169 patients were analysed using Stata. Multiple logistic regression with forward stepwise selection of variables was performed. Results Both microscopy and culture results were positive in 32% of cases and negative in 42%. Dermatophytes formed the majority of isolates. Four parameters were found to be significantly related to positive mycology results: a history of tinea pedis in the last year, scaling on one or both soles, white crumbly patches on the nail surface, and an abnormal colour of the nail plate. Conclusions Our results have shown one historical feature and three clinical features to be strongly associated with onychomycosis. The questionnaire has been revised to include only these stems and is being tested further with the aim of achieving a binary definition.