Diagnosis and prevalence of onychomycosis in diabetic neuropathic patients: an observational study

An observational study was conducted to assess the prevalence of onychomycosis in clinically suspected diabetic neuropathic patients and to assess the reliability of the diagnosis.

One hundred successive type 1 and 2 diabetic patients with diabetic neuropathy were followed. Diabetic neuropathy was defined by a vibration perception threshold greater than 25 V and onychomycosis by clinical diagnosis. Samples of the most affected nail were taken. Potassium hydroxide testing and culture were performed. Photographs of the nails were used by two dermatologists for diagnosis.

The mean +/- SE age was 62.3 +/- 11.4 years for the 20 onychomycotic patients and 60.3 +/- 10.4 years for the entire cohort; 14 onychomycotic patients (70%) were male versus 56 in the full cohort (56%) (P < .05). The prevalence of onychomycosis was 20% (culture and potassium hydroxide test positive) and 24% (culture positive). Twenty or 30 patients were positive by the potassium hydroxide test, depending on the investigator. The most frequent pathogen found was Trichophyton rubrum (11 of 20 patients; 55%). The positive predictive values of the dermatologist's diagnoses were 57.8% and 35.6%, and the negative predictive values were 85.0% and 90.5%. The two expert's results were significantly different (P < .05).

The diagnosis of onychomycosis is difficult to make. The diagnostic methods commonly used are not satisfactory. If onychomycosis is dangerous for the diabetic foot, a better diagnostic method is needed.