Interobserver reliability of the Nail Psoriasis Severity Index

Background. Because the Psoriasis Area and Severity Index (PASI) does not consider the severity of nail disease, a scale that assesses the extent of involvement of psoriatic nails is needed. A new grading system, the Nail Psoriasis Severity Index (NAPSI) has been proposed. Aims. The purpose of this study was to assess the interobserver reliability of NAPSI. Methods. The nail features of 25 patients with psoriasis with nail involvement were evaluated and graded by three dermatologists for total NAPSI scores and nail scores. The quadrants of all nails were examined for the presence of matrix and bed features. Total NAPSI score (0-160) of patients and nail score (0-32) of the individual nails were calculated. Interobserver reliability assessments were performed by computing intraclass correlation coefficients (ICC; two-way mixed model, consistency definition). Results. The ICC(3,1) results for total NAPSI score and nail score were found to be 0.781 and 0.649, respectively. The ICC(3,1) for nail-bed and nail-matrix features were 0.869 and 0.584, respectively, in the total NAPSI scoring system, and 0.705 and 0.603, respectively, in the nail scoring system. Conclusion. Moderate to good agreement of scoring with the NAPSI was determined among the observers in this study. Our results suggest that scoring for nail-bed features seems to be more reliable than scoring for nail-matrix features.