Renal abnormalities in ankylosing spondylitis

The incidence of renal abnormalities is increased in patients with ankylosing spondylitis (AS). Possible mechanisms include the effects of nonsteroidal anti-inflammatory drugs (NSAIDs), an increased incidence of glomerulonephritis and the deposition of amyloid. We assessed renal function in 51 patients with AS randomly selected from those attending routine rheumatology clinics. Five patients were found to have a definite renal abnormality and three of them underwent renal biopsy. These showed one case each of IgA glomerulonephritis, focal segmental glomerulosclerosis and nonspecific tubulo-interstitial damage. A sixth patient had recurrent haematuria and borderline renal functional impairment but refused further investigation. The urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) was elevated in four patients; two had other biochemical evidence of renal damage while the other two patients appeared normal, although they had both received spinal irradiation in the past. The finding of a significant renal abnormality in 10% of AS patients suggests that evidence of renal involvement should be actively sought in this disease.