Clinical Presentation of Multiple Myeloma Mimics Giant Cell Arteritis

Abstract

Introduction: Giant cell arteritis (GCA) is a form of immune-mediated systemic vasculitis affecting large- and medium-sized arteries. GCA and multiple myeloma share the skeletal-related clinical features such as bone pain occurring at multiple sites and fatigue, besides affecting mostly individuals aged ≥ 50 years old. Case: We present a 76-year-old lady who presented to the rheumatology department at University Hospital Limerick, Ireland, with temporal headache and right hip pain. A rheumatology review revealed the patient’s GCA probability score (GCAPS) is 10, indicating intermediate probability. Her temporal and axillary artery Doppler ultrasound scan was normal. However, the whole-body computed tomography scan of the skeletal survey revealed multiple lytic lesions. Serum protein electrophoresis recorded a high IgG level of 29.9 g/L and a high monoclonal IgG Kappa in the gamma region of 20.6 g/L. A bone marrow biopsy revealed >10% plasma cell proliferation, consistent with Multiple Myeloma (MM). Upon MM diagnosis, the patient is following the treatment protocol at the hematology department. Discussion: The presented case, initially pre-diagnosed as GCA, manifested with temporal headache and right hip pain. These symptoms align with the broad, multifaceted nature of GCA, which involves both cranial and large arteries. Literature supports the notion that GCA and MM share overlapping skeletal-related features, such as multifocal bone pain and fatigue in older adults, and reports suggest a possible inflammatory link between the two. Therefore, careful diagnosis is essential to prevent misdiagnosis and avoid unnecessary steroid treatment. Conclusion: Medical doctors are recommended to determine MM-specific CRAB features of patients who are suspected to be affected by GCA to rule out MM.