Abstract
Systemic lupus erythematosus (SLE) is a chronic, multisystem autoimmune disease that can manifest in older individuals, presenting unique diagnostic challenges because of its atypical presentations and comorbidities. Pleural effusion is a relatively uncommon manifestation of SLE, with studies suggesting a higher prevalence in older than younger patients. We herein report an atypical case of delayed-onset SLE in a 75-year-old man with left-sided pleural effusion as the initial presentation. This case underscores the difficulty of diagnosing SLE in patients of advanced age and the importance of considering a broad range of differential diagnoses, even in cases that may suggest a more common disease. This case also highlights the fact that unilateral pleural effusion can be an initial manifestation of SLE, and when the cause of the pleural effusion is unclear, SLE should be considered as a potential diagnosis.