Abstract
Polymyositis is an autoimmune multisystemic disorder that affects the body's muscular system. It usually affects the proximal muscles of the shoulder, pelvis, neck flexor muscles, and sometimes, the hip extensor muscles. However, it can also affect the diaphragm causing acute respiratory failure. This case report educates clinicians about the atypical presentation of polymyositis, diagnosis, and treatment of this disease. It also emphasizes the importance of looking for an alternative diagnosis such as polymyositis when the treatment for the more common diagnoses such as community-acquired pneumonia does not improve the patient's respiratory status.