Lupus in Disguise: Late-onset Systemic Lupus Erythematosus Presenting as Unilateral Pleural Effusion Mimicking Tubercular Pleuritis

diagnosis may lead to unnecessary antimicrobial exposure, increased morbidity, and progression of systemic disease.We describe a diagnostically challenging case of late-onset SLE presenting as unilateral pleural effusion initially treated as tubercular pleuritis, highlighting the importance of maintaining a broad differential diagnosis in persistent exudative pleural effusions. IntroductIonSystemic lupus erythematosus (SLE) is a chronic multisystem autoimmune disease characterized by immune dysregulation, autoantibody production, complement activation, and inflammatory tissue injury involving multiple organ systems.Although SLE predominantly affects women of reproductive age, late-onset disease occurring after 50 years of age is increasingly being recognized and often demonstrates atypical clinical manifestations with diagnostic delays.Thoracic involvement is common in SLE and may include pleuritis, pleural effusion, interstitial lung disease, acute lupus pneumonitis, diffuse alveolar hemorrhage, shrinking lung syndrome, pulmonary hypertension, and thromboembolic disease.Among these, pleural involvement represents the most frequent pulmonary manifestation.Pleural effusions in SLE are typically bilateral, small-to-moderate in volume, and associated with active systemic disease.Isolated unilateral pleural effusion as the initial and sole presenting manifestation is distinctly uncommon and may closely resemble infectious etiologies, particularly tuberculosis in endemic settings.Distinguishing lupus pleuritis from tubercular pleural effusion is clinically challenging because both conditions may present with fever, constitutional symptoms, lymphocytic exudative pleural fluid, and elevated pleural fluid adenosine deaminase (ADA) levels.Late-onset SLE poses additional diagnostic complexity because elderly patients often demonstrate fewer classical manifestations, lower disease activity at presentation, and greater overlap with malignancy, infection, and drug-related conditions. 1