This study is looking at how well a medicine called remibrutinib works for adults with severe chronic pruritus of unknown origin (CPUO). Pruritus means itching. CPUO is a type of itching that doctors can't find a cause for. The study will last up to 60 weeks, with different parts, including a screening time, treatment with either remibrutinib or a placebo (fake medicine) for 24 weeks, a switch for placebo participants to remibrutinib for 28 weeks, and a final safety check for 4 weeks.

Participants must be at least 18 years old and have had severe itching for at least 4 months. This itching can't be from other known causes like skin diseases or medications. They need to have itchiness affecting their trunk, arms, or legs that is severe enough to score 7 or higher on a special itch scale.

• The study involves multiple visits over 60 weeks.
• There are different phases including some with a placebo.
• Participants with certain health conditions cannot join.

This study aims to find out if the medication is safe, effective, and can be tolerated well by participants.