The course of chronic plaque-type psoriasis in placebo groups of randomized controlled studies

To determine the outcome in placebo-treated patients with plaque-type psoriasis.

Online search of MEDLINE and EMBASE until January 2001 and the Cochrane Library (2001, issue 1), supplemented by references, reviews, guidelines, and textbooks.

Randomized controlled induction of remission trials of patients with chronic plaque-type psoriasis with systemic treatments with a placebo group not treated with antipsoriatic medication. Identified studies were examined by 2 independent reviewers. Through MEDLINE, 290 studies could be identified. Twenty-seven placebo-controlled studies were included (488 patients).

Two independent reviewers extracted data on first author, year of publication, design, comparison, placebo treatment, number of patients, treatment duration, type of psoriasis and baseline severity in the placebo group, mean relative change in outcome measures, and/or percentage of patients with worsening of psoriasis; no change; minimal, moderate, or good improvement; or complete clearance.

Owing to substantial heterogeneity and differences in the way outcomes were reported, no summary estimates could be obtained. The outcome of placebo treatment was poor in most studies. Some reported a mean relative change of 11% to 47%. The highest percentages of patients ended up in the worsening, no change, or minimal improvement categories. Also, complete clearance was possible. No explanation for the differences in outcome between placebo groups could be found. Description of placebo groups was often insufficient.

The effect of treatment in placebo groups varied across studies in an unpredictable way. To evaluate the variability, improvement of the standardization of study designs, entry criteria, and outcome measures is necessary in psoriasis trials.