GLPG3667 is a medication being tested in this clinical trial for its effectiveness in treating dermatomyositis, a condition that causes muscle weakness and skin rashes. The trial aims to see how well this medication works in reducing the symptoms of the disease. Participants in the study will take this medication orally once a day for 24 weeks. The trial also includes an open-label extension phase, where all participants will receive the medication to further assess its safety and how well people can tolerate it over time. This means that after the initial study period, everyone will know they are receiving the actual medication, not a placebo, to gather more information about its long-term effects.

Dermatomyositis – Dermatomyositis is an inflammatory disease characterized by muscle weakness and a distinctive skin rash. It primarily affects the skin and muscles, leading to symptoms such as a violet or dusky red rash, often on the face, eyelids, knuckles, elbows, knees, chest, and back. Muscle weakness typically occurs in the hips, thighs, shoulders, upper arms, and neck, making it difficult to climb stairs, lift objects, or perform other daily tasks. The disease progresses with increasing muscle weakness and skin changes, which can vary in severity. Over time, dermatomyositis may also affect other organs, including the lungs and heart. The exact cause of dermatomyositis is unknown, but it is believed to involve an autoimmune response.