For my German followers: today I learned that CSU is the abbreviation for a certain kind of hives – Chronic Spontaneous Urticaria https://www.webmd.com/skin-problems-and-treatments/features/urticaria-chronic-spontaneous .
Chronic Spontaneous Urticaria: What to Know

What you should know about chronic spontaneous urticaria (CSU), including symptoms, triggers, treatment, and a link to autoimmune disease.

WebMD