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Evaluating psoriasis with Psoriasis Area and Severity Index, Psoriasis Global Assessment, and Lattice System Physician's Global Assessment

https://doi.org/10.1016/j.jaad.2004.04.012Get rights and content

Background

Reliable assessment of severity in psoriasis is essential to document treatment responses in clinical research. The reliability of current clinical outcome measures is uncertain.

Objective

To quantify the relative variation in commonly used outcome measures (the Psoriasis Area and Severity Index [PASI] and one version of the Psoriasis Global Assessment [PGA]), and a newer measure, the Lattice System Physician's Global Assessment (LS-PGA).

Methods

Physicians who were experienced (53%; 9/17) or inexperienced (47%; 8/17) in using PASI and PGA evaluated 35 patients with psoriasis in random order twice with each rating system. We assessed the variation in scoring psoriasis severity within (intrarater) and among (interrater) physicians.

Results

PASI, PGA, and LS-PGA were highly correlated (r > 0.8 for all comparisons) and had high overall reliability (Cronbach's α > 0.9 for each). PGA and LS-PGA had lower intrarater variation than PASI. LS-PGA had a 55% higher concordance coefficient between the two evaluations than did PGA. Interrater variation was lower for PGA and LS-PGA than for PASI both before and after correction for measurement error. Experience was beneficial in reducing variation in PASI scores but was not required with PGA or LS-PGA.

Conclusion

The LS-PGA, which is standardized, does not require experience, and provides discrete word-based scores with intrinsic meaning, is a reliable measure of therapeutic effect in psoriasis, and would allow comparisons across different clinical trials.

Section snippets

Methods

Thirty-five patients with psoriasis were recruited for the study from the outpatient department, phototherapy unit, and the Day Treatment Center of the University of Michigan Department of Dermatology. Dermatology nurses asked patients to participate with a goal to recruit a range of severity of psoriasis; patients gave consent and were compensated for their time. No medications were used during the study; the patients were not participating in other research studies nor were they invited to do

Relationships of the rating systems to each other

The Spearman correlation coefficients for all physicians between PASI and PGA (0.87), PASI and LS-PGA (0.86), and PGA and LS-PGA (0.83) indicate that the measures were highly correlated. (A coefficient of 1 would indicate complete agreement of the scores whereas 0 would indicate absolutely no relationship among the scores.) These relationships were similar for both experienced and inexperienced raters for PASI and PGA (0.88 vs 0.86 respectively), PASI and LS-PGA (0.87 vs 0.86), and PGA and

Discussion

In this interrater and intrarater variability study, the psoriasis assessments, PASI, PGA, and LS-PGA, were assessed twice in 35 subjects by 17 raters yielding over 3300 completed observations. The PASI, PGA, and LS-PGA were highly correlated with each other (r > 0.8 for all comparisons). We did not expect a perfect correlation, which would have indicated that the rating systems were exactly the same; yet we expected the high correlations we found because all 3 systems attempt to measure the same

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Supported by Biogen, Inc., Cambridge, Mass.

Disclosure: A patent on the Lattice System Physician's Global Assessment has been filed by Dr Ellis.

Presented in part at the International Investigative Dermatology 2003 meeting, South Miami Beach, Florida, April 30-May 4, 2003.

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