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Detection of Dermatophytes in Subclinically Involved Nails by Polymerase Chain Reaction in Patients with Skin
Daya Babu1, Reena Rai1, Lavanya Sriramajayam2
1From the Department of Dermatology, PSG Institute of Medical Sciences and Research, Coimbatore, Tamil Nadu, India.
Context:
Patients with skin dermatophytosis can have subclinical dermatophytes in the nails, which can easily be missed on clinical examination. Dermatophytes may not be isolated from normal-appearing nails by KOH and culture, where it can serve as a reservoir for recurrent infection. Detection can be made by polymerase chain reaction (PCR), a more sensitive and faster technique.
Aims:
To detect the presence of dermatophytes in clinically unaffected nails by PCR in patients with skin dermatophytosis and to evaluate the diagnostic performance of KOH, culture, and PCR in detecting subclinical nail involvement.
Materials And Methods:
In this prospective observational study, 120 patients with skin KOH positivity had their nail clippings collected and sent for KOH, PCR, and culture. Results were tabulated, and statistical analysis was done.
Results:
Out of 120 patients, nail KOH revealed that 39 patients (32.5%) tested positive for dermatophytes, while 81 (67.5%) tested negative. Nail culture on Sabouraud dextrose agar (SDA) and dermatophyte test medium (DTM) showed dermatophyte growth in 44 patients: Trichophyton mentagrophytes (15.1%), Trichophyton rubrum (12.1%), Trichophyton tonsurans (4.2%), and unidentified dermatophytes (2.4%). PCR identified dermatophytes in 57 patients (47.5%). Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of KOH compared to PCR were found to be 68.4%, 100%, 100%, 77.8%, and 85% respectively; the same parameters for culture versus PCR were found to be 77.2%, 96.8%, 95.7%, 82.4%, and 87.5%, respectively, and for PCR versus culture were found to be 100%, 82.9%, 77.2%, 100%, and 89.2%, respectively.
Conclusion:
In patients with dermatophyte infection, nail PCR can detect subclinical infection in the nail, which may serve as a reservoir for ongoing infection and recurrence.
