Polymyositis (PM) is a rare inflammatory myopathy characterized by progressive symmetrical proximal muscle weakness. Diagnosis is challenging due to clinical overlap with other myopathies, requiring biochemical markers, autoantibody profiling, electromyography (EMG), MRI, and muscle biopsy. Autoantibodies aid classification, though none are PM-specific. Management combines glucocorticoids and immunosuppressants, with prednisolone (0.75–1 mg/kg/day) as first-line therapy, gradually tapered over 12 months. Methotrexate, azathioprine, or mycophenolate mofetil are the preferred steroid-sparing agents, while an initial IV methylprednisolone pulse therapy may also be given for severe disease. Monitoring involves clinical assessments and biomarkers. Immunosuppression risks include osteoporosis, infections, and steroid myopathy, necessitating bone protection, vaccination, and cautious steroid tapering. Supervised exercise therapy improves muscle strength and should be integrated into long-term care. Given its rarity and evolving classification, continued research into novel biomarkers and targeted immunotherapies is essential for optimizing outcomes.