Is the Nail Psoriasis Severity Index reliable in the assessment of nail psoriasis by rheumatologists?

Objective: To determine the agreement and reliability of the Nail Psoriasis Severity Index (NAPSI) in the assessment of nail involvement in patients with psoriatic arthritis (PsA) when performed by rheumatologists with no experience in using this instrument.

Methods: In total, 3 women with PsA, satisfying the Classification of Psoriatic Arthritis Study Group criteria, with nail involvement were selected from an outpatient clinic devoted to PsA. The assessors consisted of 2 groups: 8 expert rheumatologists in the field of PsA who were members of the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis and had extensive experience of >10 years, and 69 rheumatologists who had never previously used the NAPSI. A video showing the nail of each selected patient (patient A, patient B, and patient C) with the most nail PsA dystrophy was shown to these 2 groups. The 8 assessors of the first group, previously trained in using the NAPSI, evaluated the 3 videos independently by using the NAPSI score. The second group scored the NAPSI after an educational session. This evaluation was repeated after 6 hours with a different sequence of videos (unpaired fashion). Interreader and intrareader reliability were estimated by calculating intraclass correlation coefficients (ICCs) and associated 95% confidence intervals (95% CIs).

Results: The interreader reliability showed ICC 0.934 (95% CI 0.7504-0.9983). Intrareader reliability showed ICC 0.463 (95% CI 0.134-0.668), ICC 0.148 (95% CI 0.3767-0.4722), and ICC 0.354 (95% CI 0.0425-0.600) for patient A, patient B, and patient C, respectively.

Conclusion: These results show that the NAPSI may be an unreliable instrument to assess nail involvement when used by untrained rheumatologists in clinical practice.