Nail psoriasis: N-NAIL shows higher diagnostic accuracy in study
- John Evans
- 3 days ago
- 1 min read
Findings from a study comparing the Nijmegen-Nail Psoriasis Activity Index Tool (N-NAIL) and Nail Psoriasis Severity Index (NAPSI) tools show that the N-NAIL, with a cutoff value of two, showed better accuracy compared to the NAPSI.
The study was published online ahead of print in the International Journal of Dermatology (24 August 2025).
Because the challenge of distinguishing nail psoriasis (NP) from nonspecific nail changes contributes to heterogeneity in clinical trials, researchers aimed to evaluate the diagnostic performance of two severity scoring tools for NP.
Including a cohort of 104 psoriasis patients—68 clinically diagnosed with NP—and matched controls, investigators scored their fingernails using the NAPSI and the N-NAIL. To determine their diagnostic properties, the researchers established cutoff values. They constructed receiver operating characteristic (ROC) curves and calculated sensitivity and specificity for various cutoff points. The authors chose the best cutoff value based on the Youden Index and clinical reasoning.
For the N-NAIL, a cutoff value of two showed the best accuracy in the psoriasis population (sensitivity=83.8% and specificity=83.3%) and the general population (sensitivity=83.8% and specificity=67.3%). For the NAPSI, a cutoff value of 7 showed the best accuracy in the psoriasis population (sensitivity=80.9% and specificity=69.4%), while a cutoff value of 10 was optimal in the general population (sensitivity=72.1% and specificity=70.2%).
“We prefer using the N-NAIL, with a cutoff value of two, because it showed better accuracy compared to the NAPSI,” the authors write in their conclusion.