Idiopathic inflammatory myopathies (IIMs) are connective tissue diseases of unknown etiology, characterized by progressive mononuclear cell infiltration in muscles. Polymyositis (PM), a rare subset of IIMs, is clinically defined by progressive proximal muscle weakness with a symmetric distribution. We present a 50-year-old female with a 3-month history of progressive proximal muscle weakness. Laboratory studies showed elevated creatine kinase (CK) and inflammatory markers, with electromyography indicating irritable myopathy. Muscle biopsy confirmed polymyositis, showing characteristic histopathological features. The patient was treated with steroids, resulting in significant improvement in muscle strength and continued remission at a one-month follow-up. This case highlights the importance of early diagnosis and treatment to prevent severe complications.