The Palmoplantar Pustulosis Area and Severity Index (PPPASI) is used to assess the severity of palmoplantar pustulosis lesions and their response to therapy. The glabrous skin of both palms and both soles are assessed for erythema, pustules, and desquamation (scaling), each on a scale from 0 (none) to 4 (very severe). The area affected of each palm and sole is scored from 0 (0%) to 6 (90-100%). Scores for the 3 characteristics of PPP are summed and adjusted for the area affected, and the scores for each palm and sole are added to calculate the total score. The PPPASI total score ranges from 0 to 72. A higher score indicates more severe disease, and a negative change from Baseline indicates improvement.

Intent-to-treat analysis set with available data

Clinical safety was evaluated by reporting incidence of adverse events up to week 24. TEAEs are defined as new events that occured during or after first dose of study drug or any event that worsens after first dose of study drug.

A serious AE (SAE) is defined as any untoward medical occurrence that resulted in death, was life-threatening, resulted in persistent disability/incapacity, was a congenital anomaly/birth defect, or an important medical event that may jeopardize the participant or require medical or surgical intervention to prevent one of the outcomes listed above.

Severity was assessed by the Investigator as mild (easily tolerated, causing minimal discomfort and not interfering with everyday activities), moderate (causes sufficient discomfort and interferes with normal everyday activities) or severe (prevents normal everyday activities).

The Investigator assessed the relationship between study treatment and each AE based on clinical judgement.

Safety Analysis Set (all randomized participants who received at least 1 dose of imsidolimab or placebo).

The Palmoplantar Pustulosis Area and Severity Index (PPPASI) is used to assess the severity of palmoplantar pustulosis lesions and their response to therapy. The glabrous skin of both palms and both soles are assessed for erythema, pustules, and desquamation (scaling), each on a scale from 0 (none) to 4 (very severe). The area affected of each palm and sole is scored from 0 (0%) to 6 (90-100%). Scores for the 3 characteristics of PPP are summed and adjusted for the area affected, and the scores for each palm and sole are added to calculate the total score. The PPPASI total score ranges from 0 to 72. A higher score indicates more severe disease.

Intent-to-treat analysis set with available data

The Investigator rated the severity of participants' disease on the following 5-point scale:

• 0: Clear - No signs of palmoplantar pustulosis; no scaling or crusts or pustules remain;
• 1: Almost clear - Slight scaling and/or erythema and/or slight crusts; very few (yellow) and/or old (brown) pustules;
• 2: Mild - Scaling and/or erythema and/or crusts; visible new (yellow) and/or old (brown) pustules of limited number and extent;
• 3: Moderate - Prominent scaling and/or erythema and/or crusting; prominent new (yellow) and/or old (brown) pustules covering most of the area involved;
• 4: Severe - Severe scaling and/or erythema and/or crusting; numerous new (yellow) and/or old (brown) pustules with / without major confluence, covering the entire area of at least 2 palmoplantar sites.

Intent-to-treat analysis set with available data