Ultrasonographic Criteria for Diagnosing Unilateral and Bilateral Retronychia

Objectives: 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.

Methods: 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.

Results: 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.

Conclusions: Ultrasonography can support the diagnosis of retronychia in unilateral and bilateral cases.