Publication:

Late-onset systemic lupus erythematosus masquerading as rheumatoid arthritis with multisystem involvement: a diagnostic challenge

Late-onset systemic lupus erythematosus (SLE), occurring after the age of 60 years, often presents with atypical features, which leads to delayed diagnosis. This report highlights how an atypical presentation led to misdiagnosis as rheumatoid arthritis, resulting in delayed recognition and diagnostic challenge of late-onset SLE. A 61-year-old Indian woman presented with a 1-year history of bilateral inflammatory symmetrical polyarthralgia involving both small and large joints which was initially treated as rheumatoid arthritis without significant improvement. Over time, she developed worsening fatigue, cold intolerance and bilateral periorbital swelling with mild bilateral pedal oedema. Investigations revealed pancytopenia, raised inflammatory markers, hypocomplementemia; strongly positive ANA (4+, homogeneous pattern, 1:640), along with positivity for anti-Ro52, anti-SSA, anti-ribosomal P protein, and ANCA-P. She had mild left ventricular systolic dysfunction (Ejection fraction of 45%), suggesting possible autoimmune cardiac involvement. HRCT thorax revealed features of interstitial lung disease (ILD) suggesting non-specific interstitial pneumonitis (NSIP) pattern. Based on clinical, serological, and immunological findings, the patient fulfilled the 2019 EULAR/ACR criteria for SLE with a score of 18, confirming the diagnosis of late-onset SLE. This case emphasizes the diagnostic difficulty of late-onset SLE, especially when classical cutaneous manifestations are absent and the disease closely resembles rheumatoid arthritis. Early consideration of autoimmune evaluation in elderly patients with unexplained multisystem involvement may help prevent delayed diagnosis and progressive organ damage.