This paper presents a clinically significant case of multiple myeloma (MM) coexisting with autoimmune disease, highlighting the diagnostic and therapeutic challenges encountered in low-resource settings. Multiple myeloma is a malignant plasma cell disorder characterized by clonal proliferation within the bone marrow and associated end-organ damage, while autoimmune diseases such as rheumatoid arthritis (RA) involve chronic immune dysregulation and inflammation. The overlap in clinical features between these conditions particularly anemia, bone pain, and elevated inflammatory markers, can obscure diagnosis and delay appropriate management. The report centers on a 58-year-old patient initially managed for autoimmune arthritis based on clinical and laboratory findings, including elevated inflammatory markers and positive autoimmune serology. Despite initial improvement with immunosuppressive therapy, the patient later developed additional symptoms such as fatigue, renal abnormalities, and bone pain. Further investigations revealed hallmark features of MM, including lytic bone lesions, Bence Jones proteinuria, and monoclonal gammopathy confirmed by serum protein electrophoresis and bone marrow biopsy. The patient was subsequently treated with chemotherapy, resulting in clinical improvement. This case underscores the complex interplay between chronic immune activation and malignant transformation, supporting the hypothesis that prolonged antigenic stimulation in autoimmune diseases may predispose to plasma cell dyscrasias. It also highlights the importance of maintaining a high index of suspicion when patients with autoimmune conditions present with atypical or progressive symptoms. Early recognition and multidisciplinary collaboration are critical for improving outcomes. The study emphasizes the need for better diagnostic access, clinician awareness, and healthcare support systems, particularly in resource-limited environments.