Palmoplantar pustulosis is a chronic inflammatory skin disease that causes repeated on and off symptoms like erythema (reddening, irritation), vesicle (swelling, cyst), pustules, scale, and crusts in palms and soles. This study evaluates how well risankizumab works compared to placebo (no medicine) to treat palmoplantar pustulosis. Study will assess change in Palmoplantar Pustulosis Area and Severity Index [PPPASI].

Risankizumab is an investigational drug being developed for the treatment of palmoplantar pustulosis. This study is "double-blinded", which means that neither the trial participants nor the study doctors will know who will be given study drug and who will receive placebo (no medicine). Participants are randomly put into 1 of 2 groups, called treatment arms to receive risankizumab or placebo in period A. In period B, each group receives both risankizumab and placebo at different time intervals. Around 116 adult participants with palmoplantar pustulosis will be enrolled in approximately 39 sites across Japan.

Participants will receive subcutaneous (SC) injections of risankizumab or placebo at Week 0 and Week 4 (Period A). Beginning Week 16 (Period B), both the groups will receive risankizumab and placebo at different intervals. Total treatment duration is 56 weeks.

There may be a higher burden for participants in this trial compared to their standard of care. Participants will attend regular visits during the course of the study at a hospital or clinic. The effect of the treatment will be checked by medical assessments, blood tests, checking for side effects and completing questionnaires.

Inclusion Criteria:

• Stable moderate to severe Palmoplantar Pustulosis (PPP) with a Palmoplantar Pustulosis Area and Severity Index (PPPASI) total score of >= 12 at the Screening and Baseline Visits.
• Moderate or severe pustules/vesicles on at least one palm or sole (>= 2 PPPASI severity score) at the Screening and Baseline Visits.
• Experienced inadequate response (or intolerant) to treatment with topical corticosteroids and/or vitamin D3 derivative preparations and/or phototherapy and/or systemic etretinate.

Exclusion Criteria:

- History of active skin disease other than PPP which could interfere with the assessment of PPP.

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