Coexistence of systemic lupus erythematosus and sarcoidosis: A case-based review.

Sarcoidosis and systemic lupus erythematosus (SLE) are chronic multisystem inflammatory diseases with distinct pathogenetic mechanisms but overlapping clinical and immunological features. Their coexistence is exceedingly rare and may result in diagnostic delay or misinterpretation of disease activity. A 50-year-old woman presented with photosensitive facial rash, oral ulcers, constitutional symptoms, cytopenia, hypocomplementemia, and markedly elevated anti-double-stranded DNA titers, fulfilling the 2019 ACR/EULAR classification criteria for SLE. During follow-up, atypical cutaneous lesions involving the external auditory canal were identified. Histopathological examination revealed non-caseating granulomatous inflammation. Further evaluation with thoracic imaging and endobronchial ultrasound-guided biopsy demonstrated bilateral hilar and mediastinal lymphadenopathy with granulomatous inflammation, confirming the diagnosis of sarcoidosis. Treatment with hydroxychloroquine, systemic corticosteroids, and methotrexate led to significant clinical and laboratory improvement over a six-month follow-up period. This case highlights the importance of considering a coexisting diagnosis when atypical clinical or histopathological findings emerge in patients with established autoimmune disease, with histological confirmation playing a central role in accurate diagnosis.