Table 1 Definitions of commonly-used terminology used by the US National Psoriasis Foundation (NPF), the European Medicines Agency (EMEA) and this study.

During treatment

Flare

Typical or unusual worsening of disease during treatment and/or the occurrence of new psoriasis morphologies.

Not defined.

Not used

Following treatment discontinuation

Recurrence

Not defined

The EMEA recommend the use of recurrence as an endpoint in long-terms studies provided that it is clearly defined.

The term 'inflammatory recurrence' includes (a) patients with worsening of psoriasis within 2 months of discontinuation from efalizumab treatment to a level less severe than a rebound and (2) patients who have discontinued a psoriasis treatment due to an inflammatory disease flare but, following discontinuation, require treatment to prevent a rebound.

Relapse

Loss of 50% of PASI improvement from baseline in patients who achieve a clinically meaningful response (≥ 50% improvement in PASI score from baseline).

A reduction of >50% in PASI from the achieved maximal improvement in PASI score.

Subjective alternative: a relapse of psoriasis necessitating the re-initiation of treatment.

A simple worsening of psoriasis beyond 2 months of therapy may represent the natural course of the disease (relapse) rather than a rebound associated with drug.

Not used

Rebound

A PASI of 125% of baseline or new generalized pustular, erythrodermic, or more inflammatory psoriasis occurring within 3 months of stopping therapy.

Worsening occurring after 3 months of therapy may represent the natural course of the disease rather than a rebound associated with the drug.

Worsening of psoriasis over baseline value (e.g. PASI>125%) or new pustular, erythrodermic or more inflammatory psoriasis occurring within 2 months of stopping therapy.

A 2-month boundary separating relapse and rebound is drawn on theoretical grounds and is more or less arbitrary.

Not used