The Physician’s Global Assessment of Fingernail Psoriasis (PGA-F), a relatively new clinician-rating severity scale, was a reliable and quick method capable of categorizing the severity of fingernail psoriasis. Findings from this study were reported in the Journal of the European Academy of Dermatology and Venereology.

The PGA-F synthesizes ratings across several nail severity components into 1 out of 5 different classifications, ranging from clear to severe. According to the study investigators, the advantage of this system is that the total scores are easy to interpret but retain their clinical importance.

In this study, researchers assessed the validity and inter-rater reliability of the PGA-F measure. The investigators first performed cognitive interviews with 10 practicing dermatologists to examine the measure’s clarity, relevance, and comprehensiveness. In addition, the researchers tested the inter-rater reliability (IRR) of ratings from 22 dermatologists and 8 clinical trial investigators using many-facet Rasch analysis.


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The cognitive interviews confirmed the instrument’s content validity. All practicing dermatologists agreed the clinical criteria in the PGA-F were consistent with nail psoriasis, and the training photographs were deemed as realistic representations of the disease. Approximately 70% of participants were able to discriminate between clear, mild, and moderate categories.

Some of the participants (40%) suggested the instrument was “too picky” or “cumbersome” to use in regular clinical practice. Modifications suggested by the participants included reducing the number of severity categories from 5 to 3 levels, minimizing the level of detail needed to determine severity, and integrating evaluation of the nail bed as well as the matrix.

Overall, the clinician reliability exceeded the acceptability threshold for dermatologists (0.85), in addition to clinical trial investigators (0.73).

The investigators also examined the concurrent validity of the PGA-F vs the modified Nail Psoriasis Severity Index (mNAPSI) at screening and baseline. The researchers found adequate correlation (>0.30) between the 2 instruments at baseline and at 26 weeks.

A possible limitation of this study was the recruitment of only dermatologists, rather than the inclusion of clinicians from other specialties who might first see patients with fingernail psoriasis.

In spite of this limitation, the investigators wrote it is expected “the PGA-F will be a valuable outcome measure in clinical practice, especially in clinical research settings where high levels of precision are required.”

Disclosure: This clinical trial was supported by AbbVie. Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.

Reference

Hudgens S, Rich P, Geng Z, Williams D, Fleischer A, Ganguli A. Development and validation of the Physician’s Global Assessment of Fingernail Psoriasis. Published online May 20, 2021. J Eur Acad Dermatol Venereol. doi:10.1111/jdv.17387