Membranous nephropathy in ankylosing spondylitis: a rare case report.

Ankylosing spondylitis (AS) is a chronic inflammatory disease that typically affects the axial skeleton. Renal involvement is rare in AS, only occurring in 5-13% of AS patients. Membranous nephropathy (MN) in patients with AS is extremely rare. There have been only a few cases showing the association between MN and AS. Herein we report a case of AS-associated MN in a 47-year-old male. He was diagnosed with AS-associated MN after renal biopsy, and he was treated with corticosteroids and cyclophosphamide. His low back pain and oedema disappeared gradually and serum albumin and urine protein excretion significantly improved after treatment. In clinical practice, AS patients with proteinuria or renal dysfunction should be evaluated for MN through ‌serum anti-phospholipase A2 receptor autoantibody (anti-PLA2R antibody) testing‌ and ‌renal biopsy‌ to confirm diagnosis.