Diagnostic dilemma: Differentiating coexisting systemic lupus erythematosus and Sjögren's syndrome mimicking multiple myeloma in a patient with hypergammaglobulinemia presenting to primary care - A case report.

Introduction: Systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS) are chronic autoimmune diseases that can coexist, complicating the diagnostic process due to overlapping clinical and serological features. Hypergammaglobulinemia, often associated with these conditions, can mimic hematological malignancies, posing a significant diagnostic challenge.

Case presentation: We report a case of a 57-year-old woman presenting with progressive fatigue, dry cough, and vasculitic rashes for several weeks. Initial laboratory results revealed pancytopenia, hypergammaglobulinemia, and elevated inflammatory markers (erythrocyte sedimentation rate (ESR) >100 mm/hr, C-reactive protein (CRP) 137.7 mg/L), raising suspicion for multiple myeloma. However, protein electrophoresis (which showed polyclonal rather than monoclonal globulinemia) and bone marrow biopsy excluded malignancy. Further autoimmune screening confirmed coexisting SLE and SS, with positive ANA (≥1:1280), anti-dsDNA, anti-Ro, and anti-La antibodies. Polyclonal hypergammaglobulinemia was attributed to these autoimmune conditions. The patient responded well to azathioprine and hydroxychloroquine, with significant clinical and biochemical improvement.

Discussion: This case highlights the importance of distinguishing polyclonal hypergammaglobulinemia due to autoimmune diseases from monoclonal gammopathies such as multiple myeloma. Early autoimmune screening and multidisciplinary collaboration were essential in achieving an accurate diagnosis and appropriate management.

Conclusion: Polyclonal hypergammaglobulinemia in the presence of elevated inflammatory markers warrants a thorough differential diagnosis to distinguish autoimmune conditions from hematological malignancies. This case underscores the critical role of comprehensive autoimmune screening in guiding timely and accurate diagnosis.