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Background Current treatment options for Palmoplantar Pustulosis (PPP), a debilitating chronic skin disease which affects the hands and feet, are limited. The Anakinra for Pustular psoriasis: Response in a Controlled Trial (APRICOT) aims to determine the efficacy of anakinra in the treatment of PPP. This article describes the statistical analysis plan for the final analysis of this two-staged trial, which was determined prior to unblinding and database lock. This is an update to the published protocol and stage one analysis plan. Methods APRICOT is a randomised, double-blind, placebo-controlled trial of anakinra versus placebo, with two stages and an adaptive element. Stage one compared treatment arms to ensure proof-of-concept and determined the primary outcome for stage two of the trial. The primary outcome was selected to be the change in Palmoplantar Pustulosis Psoriasis Area and Severity Index (PPPASI) at 8 weeks. Secondary outcomes include other investigator-assessed efficacy measures of disease severity, participant-reported measures of efficacy and safety measures. This manuscript describes in detail the outcomes, sample size, general analysis principles, the pre-specified statistical analysis plan for each of the outcomes, the handling of missing outcome data and the planned sensitivity and supplementary analyses for the second stage of the APRICOT trial. Discussion This statistical analysis plan was developed in compliance with international trial guidelines and is published to increase transparency of the trial analysis. The results of the trial analysis will indicate whether anakinra has a role in the treatment of PPP. Trial registration ISCRTN, ISCRTN13127147. Registered on 1 August 2016. EudraCT Number 2015-003600-23. Registered on 1 April 2016.

Background Palmoplantar pustulosis is a rare but painful and debilitating disease. It consistently ranks the highest of all psoriasis phenotypic variants in terms of symptoms and functional impairment. Management of plaque-type psoriasis has been revolutionised in the last 10 years with the advent of biologic therapies, but treatment options for pustular psoriasis remain profoundly limited. On the basis of mechanistic findings which suggest a key pathogenic role for interleukin (IL)-1 in pustular psoriasis, we hypothesise that anakinra (IL-1 blockade) will be an efficacious treatment for pustular psoriasis. Methods/design We will conduct a two-stage, adaptive, double-blind, randomised, placebo-controlled trial to test the hypothesis that anakinra, self-administered daily by subcutaneous injection over 8 weeks, will deliver therapeutic benefit in palmoplantar pustular psoriasis, a localised form of pustular psoriasis typically involving the palms and/or soles. Safety outcomes will be collected for 20 weeks. A total of 64 participants will be randomised to anakinra or placebo in a 1:1 ratio. At the end of stage 1, a decision to progress to stage 2 will be made. This decision will take place after 24 participants have been randomised and followed for 8 weeks and will be based on the ordering of the observed mean outcome values in both treatment arms. At the end of stage 1, the reliability of outcome measurements and method to collect the data will also be assessed, and the primary outcome will be confirmed for stage 2. Discussion We have undertaken an adaptive approach in which we will gain proof-of-concept data prior to completing a powered efficacy trial because pustular psoriasis is a rare disease, no validated outcome measures to detect change exist, and limited safety data for anakinra exist in this population. To our knowledge, this will be the first randomised controlled trial that will provide valuable evidence for the efficacy and safety of IL-1 blockade for treatment in pustular psoriasis. Trial registration ISRCTN13127147. Registered on 1st August 2016. EudraCT, 2015-003600-23. Registered on 1st April 2016. Electronic supplementary material The online version of this article (10.1186/s13063-018-2841-y) contains supplementary material, which is available to authorized users.

Our group identified recessive mutations of the IL36RN gene in patients affected by Generalised Pustular Psoriasis (GPP), a severe skin disorder characterised by acute episodes of pustulation, fever and systemic upset.