Fibromyalgia (FM) presents a diagnostic challenge due to its complex symptoms and lack of definitive tests. This study discusses a 54-year-old female initially diagnosed with FM, characterized by widespread pain, fatigue, and tender points. Despite treatment, she developed elevated C-reactive protein (CRP) and anemia after two years, leading to further investigations. These tests revealed non-secretory multiple myeloma, underscoring the importance of vigilant monitoring in FM patients. This case highlights the need for regular CRP measurements and thorough follow-up to detect underlying conditions. Early detection and appropriate intervention are crucial in managing FM and improving patient outcomes.