Is the nail psoriasis severity index reliable in the assessment of nail? Reliable assessment of disease is important in patient care, clinical trials, and longitudinal observational studies. Many studies have evaluated the effectiveness of various therapies for nail psoriasis, assessing clinical improvement in a global manner or in a target nail.
The NAPSI is a scale that is simple and quick to calculate; it is used to evaluate the severity of nail psoriasis, and it was developed to evaluate the response to the treatment of psoriatic nails in clinical trials. Recently, a review on the role of the NAPSI to assess the use of biologic agents in the treatment of nail psoriasis showed that it measures the improvement induced by treatment, meaning it has a good sensitivity to change.
In a previous study, there was substantial to excellent agreement among expert dermatologists and rheumatologists on the assessment of nails, but it was not determined whether the assessments of the NAPSI by rheumatologists who were not involved in clinical trials were reliable in real life. Conversely, the group of assessors in the present study was characterized by clinicians treating only patients with PsA as practitioners and without a metrology approach. Indeed, these rheumatologists could represent the majority of physicians working in the outpatient clinics in Italy.
The results showed that one-third of the rheumatologists that had never used the NAPSI for the assessment of nail involvement in patients with PsA agreed with the score of the expert rheumatologists. Moreover, the interreader reliability was high, and this result was also shown in other studies. Nevertheless, intrareader reliability showed a variable agreement in the different patients. In fact, the ICCs were moderate (patient A), poor (patient B), and fair (patient C).
In fact, the scoring process for nails using the NAPSI could be relatively easy when classic lesions are present, but very difficult in the case of concomitant lesions where a ceiling effect of the NAPSI could be obtained. In other words, when used in complicated nail conditions, the NAPSI could be too difficult for an untrained rheumatologist to use, therefore confirming that it is an unreliable instrument in these situations.
Another explanation could be the insufficient training of the assessors; longer training could have positively affected the final score. We tried to be comprehensive in the training course. Of course, a more thorough study would have consisted of real patient evaluations and untrained doctors with aLatin square design, with more lengthy training and more examples as a test before the exercise.
Nevertheless, the large number of rheumatologists did not allow us to adopt this statistical approach. However, GRAPPA also has an educational mission to implement the knowledge of all aspects involving patients with PsA, and this study could suggest pursuing this goal, since there is a need to obtain more reliable and feasible instruments to assess all the domains of PsA in daily clinical practice.
In conclusion, objective measurements of clinical improvement or worsening of nail psoriasis are of value in guiding medical therapy and standardizing clinical trials.
Source: onlinelibrary.wiley.com
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