- Objective: Patients with Myasthenia gravis (MG) are characterized by muscle weakness that may cause obstructive sleep apnea (OSA). The use of a continuous positive airway pressure (CPAP) device is often needed in order to maintain free breathing during the night and sometimes even during the day. Clinical Presentation: A 29-year-old MG patient is presented who used a CPAP continuously since the age of 12. Tight fitting of a nasal mask applied enough force to cause severe maxillary deformity. Clinical Relevance: Masks with additional forehead and chin support or a regular full face mask are recommended for patients with muscle weakness, in order to spread forces more evenly.