A Study to Understand How Nerandomilast Works in People With Active Idiopathic Inflammatory Myopathies

This study is open to adults aged 18 and older who have a condition known as active idiopathic inflammatory myopathy (IIM) or myositis. People can participate if they have a specific type of myositis. The purpose of this study is to find out whether a medicine called nerandomilast improves IIM symptoms. Participants are put into 2 groups randomly, which means by chance. One group takes nerandomilast tablets and the other group takes placebo tablets. Placebo tablets look like nerandomilast tablets but do not contain any medicine. Participants take nerandomilast or placebo twice a day for 1 year. Participants are in the study for about 1 year and 2 months. During this time, they visit the study site at least 16 times. During this time, doctors regularly check the participant's health, IIM symptoms, and take note of any unwanted effects. Participants fill in questionnaires about their IIM symptoms and how IIM impacts their quality of life. The results are compared between the 2 groups to see whether the treatment works.

Inclusion criteria: 1. Male or female adult individuals from ≥18 years of age (or alternative age for adults based on local regulations) on the date of signing the informed consent. 2. A definite or probable clinical diagnosis of idiopathic inflammatory myopathy (IIM) according to the 2017 American college of rheumatology (ACR)/European alliance of associations of rheumatology (EULAR) classification criteria. 3. Participants with overlap myositis (OM) must have IIM as the predominant disease. 4. Participants ≥18 years of age (or alternative age for adults based on local regulations) with juvenile dermatomyositis (JDM) can only be included if they were 15 years old or older at first onset of DM symptoms. 5. Disease activity defined by moderate to severe myopathy. 6. The participant must be on background therapy for IIM. 7. Woman (or women) of childbearing potential (WOCBP) must be ready and able to use highly effective methods of birth control for a period of 28 days before treatment initiation, throughout the trial, and for a period of at least 5 days after the last dose of investigational medicinal product (IMP). WOCBP taking oral contraceptives also have to use one barrier method. 8. Signed and dated written informed consent in accordance with ICH-GCP and local legislation prior to admission to the trial. 9. Further inclusion criteria apply. Exclusion criteria: 1. Major surgery (major according to the investigator's assessment, e.g. hip replacement) performed within 6 weeks prior to randomisation or planned during the trial period. 2. Any documented active or suspected malignancy or history of malignancy within 5 years prior to screening, except appropriately treated basal cell carcinoma of the skin, or in situ squamous cell carcinoma of the skin, or in situ carcinoma of uterine cervix. 3. Participants who must or wish to continue the intake of restricted medications or any drug considered likely to interfere with the safe conduct of the trial. 4. Participants diagnosed with advanced interstitial lung disease (ILD). 5. Severe muscle damage. 6. Further exclusion criteria apply.