Membranous glomerulonephritis in a patient with ankylosing spondylitis: a rare association

Ankylosing spondylitis is a chronic inflammatory disease of the vertebral joints and soft tissues. Renal involvement, apart from amyloidosis, is rare in this disorder. Of the various glomerulonephritides reported in association with ankylosing spondylitis, IgA nephropathy is the most common. Membranous glomerulonephritis occurs very rarely in patients with ankylosing spondylitis, and only four such cases have been reported in the available English literature. Due to the rarity of this association, membranous glomerulonephritis may not initially be considered in patients with ankylosing spondylitis and proteinuria. We report the case of a 29-year-old man with ankylosing spondylitis who presented with pedal edema and was detected to have nephrotic syndrome. A percutaneous renal biopsy showed features of membranous glomerulonephritis with capillary wall granular deposits of IgG and C3 on immunofluorescence and subepithelial immune complex deposits on electron microscopy. No other secondary cause of membranous glomerulopathy was found on extensive investigations. Membranous glomerulonephritis is extremely rare in association with ankylosing spondylitis, the present case being the fifth such report. The exact relationship of these two entities (etiological or coincidental) still needs to be elucidated. The occurrence of this rare association needs to be recognized and differentiated from other more common causes of renal involvement in ankylosing spondylitis.