Ultrasonographic Criteria for Diagnosing Unilateral and Bilateral Retronychia.

Abstract

To assess the main characteristics of retronychia on ultrasonography (US) and to propose US criteria for diagnosing unilateral and bilateral cases according to the digit. We conducted a case-control study with retrospective, descriptive, and statistical analyses of the US images of 210 nails: 43 with retronychia and 167 normal nails. The Student t test, Fisher exact test, and Kruskal-Wallis test, among other tests, were performed. P < .05 was considered significant. Seventy percent of the patients were females, and the most affected digit was the big toe. Significant US diagnostic criteria were as follows: criterion 1, hypoechoic halo surrounding the origin of the nail plate; criterion 2, distance between the origin of the nail plate and the base of the distal phalanx of 5.1 mm or less in big toes and thumbs and/or a difference of 0.5 mm of this distance or greater between the affected nail and the contralateral healthy nail; and criterion 3, proximal nail fold thickness of 2.2 mm or greater for male patients or 1.9 mm or greater for female patients and/or a proximal nail fold 0.3 mm thicker or greater in comparison with the contralateral healthy nail. Cutoff points, sensitivity, and specificity with a 95% confidence interval were defined for each criterion according to the digit in cases with unilateral and bilateral involvement. Ultrasonography can support the diagnosis of retronychia in unilateral and bilateral cases.