Evaluating psoriasis severity: limitations of the PASI and advantages of the overall lesional assessment

Abstract

Background: A variety of measures have been used to evaluate the severity of psoriasis. The Psoriasis Area and Severity Index (PASI) has been one of the most frequently reported but has several limitations that can impair its accuracy and clinical usefulness. First, it involves estimating the % body surface area (BSA) involvement, for which there is high inter-observer variability particularly in patients with limited psoriasis. As a result, the PASI is poor in detecting changes in mild or moderate psoriasis (the most prevalent types of psoriasis). Second, patients with very different clinical manifestations of psoriasis could have the same PASI score (eg, if one has widespread but minimal psoriasis and another has localized but severe psoriasis). Third, because plaque elevation, scaling, and erythema are rated equally, treatments that temporarily affect scaling or erythema will affect the PASI score more than equally effective treatments that do not.The OLA: In an effort to overcome some of these limitations, the Overall Lesional Assessment (OLA) has been developed. The OLA is a measure of the physician’s clinical judgment of a patient’s overall lesional severity. It avoids the inaccuracies associated with estimating %BSA and emphasizes the importance of plaque elevation (the product of hyperproliferation and disordered differentiation of keratinocytes) as the most important feature of psoriasis by giving it greater significance than erythema and scaling. The OLA thus facilitates more accurate and clinically relevant assessments of the severity of psoriasis.OLA definitions (abbreviated): ∗0 (none): no plaque elevation or scale, may have residual non-erythematous discoloration; 1 (minimal): essentially flat with possibly trace elevation, no scale, up to moderate erythema; 2 (mild): slight elevation, fine scales with some lesions partially covered, up to moderate erythema; 3 (moderate): moderate elevation with rounded or sloped edges, coarser scales with most lesions partially covered, moderate erythema; 4 (severe): marked elevation with hard sharp edges, coarse thick scales with virtually all lesions covered and a rough surface, severe erythema; 5 (very severe): very marked elevation with very hard sharp edges, very coarse thick scales with all lesions covered and a very rough surface, very severe erythema.The OLA score is determined by the written definitions. Photographs and illustrations are also used as general guides to the appearance of each grade. Background: A variety of measures have been used to evaluate the severity of psoriasis. The Psoriasis Area and Severity Index (PASI) has been one of the most frequently reported but has several limitations that can impair its accuracy and clinical usefulness. First, it involves estimating the % body surface area (BSA) involvement, for which there is high inter-observer variability particularly in patients with limited psoriasis. As a result, the PASI is poor in detecting changes in mild or moderate psoriasis (the most prevalent types of psoriasis). Second, patients with very different clinical manifestations of psoriasis could have the same PASI score (eg, if one has widespread but minimal psoriasis and another has localized but severe psoriasis). Third, because plaque elevation, scaling, and erythema are rated equally, treatments that temporarily affect scaling or erythema will affect the PASI score more than equally effective treatments that do not. The OLA: In an effort to overcome some of these limitations, the Overall Lesional Assessment (OLA) has been developed. The OLA is a measure of the physician’s clinical judgment of a patient’s overall lesional severity. It avoids the inaccuracies associated with estimating %BSA and emphasizes the importance of plaque elevation (the product of hyperproliferation and disordered differentiation of keratinocytes) as the most important feature of psoriasis by giving it greater significance than erythema and scaling. The OLA thus facilitates more accurate and clinically relevant assessments of the severity of psoriasis. OLA definitions (abbreviated): ∗0 (none): no plaque elevation or scale, may have residual non-erythematous discoloration; 1 (minimal): essentially flat with possibly trace elevation, no scale, up to moderate erythema; 2 (mild): slight elevation, fine scales with some lesions partially covered, up to moderate erythema; 3 (moderate): moderate elevation with rounded or sloped edges, coarser scales with most lesions partially covered, moderate erythema; 4 (severe): marked elevation with hard sharp edges, coarse thick scales with virtually all lesions covered and a rough surface, severe erythema; 5 (very severe): very marked elevation with very hard sharp edges, very coarse thick scales with all lesions covered and a very rough surface, very severe erythema. The OLA score is determined by the written definitions. Photographs and illustrations are also used as general guides to the appearance of each grade.