Screening for tinea unguium by thermography in older adults with subungual hyperkeratosis

Aim: The purpose of the present study was to assess the difference in foot temperature between tinea unguium-positive older adults with subungual hyperkeratosis and tinea unguium-negative older adults with subungual hyperkeratosis to develop a temperature-based screening method for tinea unguium. Methods: The present cross-sectional, observational study investigated 51 residents with subungual hyperkeratosis in two facilities covered by long-term care insurance between October 2011 and December 2011. One dermatologist recorded the clinical signs of abnormal toenails. Nail specimens were collected from all abnormal nails, and the presence of tinea unguium was confirmed when fungus was detected by direct microscopy. Foot temperature was measured by infrared thermography. A receiver operating characteristic curve was used to assess the ability to determine whether residents with subungual hyperkeratosis have tinea unguium and to determine the cut-off point. Results: Among the people with subungual hyperkeratosis, the mean toe temperature in the tinea unguium-positive group (30.2±2.6°C) was significantly lower than that in the tinea unguium-negative group (32.8±3.2°C, P=0.001). The area under the receiver operating characteristic curve was 0.74 (95% confidence interval 0.621-0.876), and the threshold temperature was set at 33.0°C, resulting in a sensitivity of 81.8% and specificity of 65.7%. Conclusion: Our study suggests that foot temperature can be used to screen for tinea unguium in people with subungual hyperkeratosis. This non-invasive and simple screening method would help clinicians to set priorities in terms of carrying out direct microscopy to diagnose tinea unguium in elderly residents in care facilities.