Unmasking Focal Segmental Glomerulosclerosis in a Patient With Lupus Nephritis.

Systemic lupus erythematosus (SLE) is a persistent autoimmune disease where the immune system produces autoantibodies against nuclear and cytoplasmic antigens, leading to multi-organ involvement. Typically, nephrotic-range proteinuria is indicative of proliferative or membranous lupus nephritis. However, on rare occasions, patients with SLE and nephrotic syndrome may exhibit focal segmental glomerulosclerosis (FSGS) lesions upon kidney biopsy. We describe a 28-year-old Middle Eastern male with SLE and biopsy-proven lupus nephritis who experienced a significant increase in proteinuria and creatinine levels despite treatment with mycophenolate mofetil. Further investigation revealed FSGS without active lupus nephritis. The patient's treatment regimen was adjusted to rituximab in response to these findings. This case underscores the importance of renal biopsies in SLE management to accurately diagnose and tailor treatment. It highlights the need to consider alternative renal complications, such as FSGS, which can coexist with lupus nephritis, necessitating a collaborative approach between rheumatologists and nephrologists to achieve optimal patient outcomes.