Subclinical onychomycosis is associated with tinea pedis

Summary Background  Onychomycosis is a common cause of nail dystrophy and may be associated with tinea pedis. The presence of dermatophyte fungi in clinically normal nails is unknown.

Objectives  To assess the presence of dermatophyte fungi in normal-appearing toenails and to compare the risk of subclinical dermatophytosis in patients without and with concurrent tinea pedis.

Methods  This is a prospective, University-based study of adults without and with microscopically confirmed tinea pedis. Subjects with dystrophy of any toenail were excluded, as were those ever previously diagnosed as having onychomycosis and those who had used topical antifungals in the past year. A great toenail clipping obtained from each subject was submitted for periodic acid–Schiff histology.

Results  One hundred and one subjects (63 men and 38 women, mean ± SD age 45·4 ± 15·7 years) were included. Overall, septate hyphae (ostensibly dermatophyte) were identified in seven specimens. Of the 66 control subjects, one case (1·5%) of nail dermatophyte was identified. Of the 35 subjects with tinea pedis, six cases (17%) of nail dermatophyte were identified (P = 0·0066; odds ratio 13·4, 95% confidence interval 1·6–117). There were no significant differences in age or gender between the experimental and control groups or between the nail dermatophyte-positive and negative cohorts.

Conclusions  Dermatophyte fungi may be isolated from normal-appearing toenails. The presence of dermatophytes in this situation is strongly associated with the presence of tinea pedis. Subclinical dermatophyte in the nail plate may serve as a reservoir for ongoing local infection.